Intermembrane space of mitochondrion

2024-10-28T05:47:15Z

Vipul: /* Definition */

{{component of organelle|mitochondrion}}

==Definition==

The '''intermembrane space of mitochondrion''' ('''IMS'''), also known as the '''perimitochondrial space''', is a space between the two membranes of a [[mitochondrion]]: the [[outer mitochondrial membrane]] (bounding it on the outside, and separating it from the [[cytosol]] or adjacent mitochondria in the [[mitochondrial network]]) and [[inner mitochondrial membrane]] (bounding it on the inside, and separating it from the [[mitochondrial matrix]]).

==Summary==

{| class="sortable" border="1"
! Item !! Value
|-
| Type of organisms whose cells contain the intermembrane space || Same as the organisms whose cells contain mitochondria: [[eukaryotic cell]]s ''only'', including [[plant cell]]s, [[animal cell]]s, and the cells of [[protist]]s and [[fungus|fungi]]
|-
| Type of cells within the organisms that contain the intermembrane space || Same as the cells that contain mitochondria: all cells except [[red blood cell]]s in [[mammal]]s (other vertebrates ''do'' have mitochondria in their red blood cells).
|-
| Number of intermembrane spaces per cell || Same as the number of mitochondria: 1 to 1000s, depending on the energy needs of the cell
|-
| Size || <math>~200</math> angstrom or <math>~20 nm</math> thickness (very approximate), accounting for less than 5% of the length (less than 10% even if you consider that it's on both sides).
|-
| Location within the mitochondrion || It is right inside of the boundary of the mitochondrion (the boundary is the [[outer mitochondrial membrane]]).
|-
| What's on both sides of it || Inside: [[inner mitochondrial membrane]] (separating it from the [[mitochondrial matrix]]), outside: [[outer mitochondrial membrane]] (separating it from the [[cytosol]] or adjacent mitochondria in the [[mitochondrial network]])
|-
| Structural components || The ''intracristal space'' is the part of the intermembrane space between the folds (cristae) of the inner mitochondrial membrane. The ''peripheral space'' is the part of the intermembrane space farther out of the inner mitochondrial membrane.
|-
| pH || About 7.0 to 7.4. Although still a little alkaline, it is less so than the mitochondrial matrix and less so than the rest of the cell, due to the pumping out of protons from the mitochondrial matrix as part of the [[electron transport chain]].
|}

==Size and shape==

===Limitations of study===

Unlike the [[mitochondrion]] as a whole, the intermembrane space of mitochondrion is too small to be seen with a light microscope. The electron microscope that is necessary to see it can be destructive to the living cell and may change the shape of the mitochondrion.

===Shape===

The entire mitochondrion (bounded by the [[outer mitochondrial membrane]]) can be approximated as a rounded cylinder (cylinder with rounded edges) and the mitochondrial matrix (bounded by the [[inner mitochondrial membrane]]) can be approximated as a rounded cylinder that is fully inside it. The intermembrane space is the region that's in the bigger rounded cylinder and outside the smaller rounded cylinder, and its thickness (up to 20 nm) represents the margin around the smaller cylinder.

This crude description captures the concept of the peripheral intermembrane space. The intracristal space is a bunch of little crevices in the inner cylinder.

===Size and volume calculation===

We use this size range for the mitochondrion:

* The length is generally at least 1 <math>\mu m</math> and at most 4 <math>\mu m</math>.
* The tubular radius is generally at least 0.5 <math>\mu m</math> and at most 1 <math>\mu m</math>.

We also use that the thickness of the intermembrane space is about 20 <math>nm</math>.

Illustratively, and using the biggest size estimates, let's say the mitochondrion has a length of 4 <math>\mu m</math>, a tubular radius of 1 <math>\mu m</math>, and an intermembrane space that is uniformly 20 <math>nm</math> thickness. Let's model the mitochondrion and mitochondrial matrix as cylinders.

* Volume of the mitochondrion is <math>\pi r^2 h</math> where <math>r = 1 \mu m, h = 4 \mu m</math>, giving <math>12.57 \mu m^3</math>
* Volume of the mitochondrial matrix (the inner cylinder) is <math>\pi r^2 h</math> where <math>r = 0.98 \mu m, h =3.96 \mu m</math> (these values are obtained by subtracting the thickness of the IMS from the radius and twice the thickness of the IMS from the height), giving <math>11.95 \mu m^3</math>. The difference is <math>0.62 \mu m^3</math>.

A cubic micrometer (<math>\mu m^3</math>) is the same as a femtoliter, or <math>10^{-15}</math> liters. So the volume of the intermembrane space works out to be <math>0.62 fL</math>. But this is the upper end. The lower end would be roughly about 1/16 of this, or about <math>0.04 fL</math>.

Note that this calculation is most faithful for the peripheral IMS. The intercristal IMS is not covered here, but likely does not cover much volume (its significance is more in terms of the high surface area that it covers, not the volume).

===Mass===

Since [[most cellular matter is approximately as dense as water]], we can approximate the density of the intermembrane space using the density of water, which is about 1 gram per milliliter. Based on the volume estimate above, we get that the mass of a mitochondrion is approximately between 0.04 and 0.62 picograms, where a picogram is <math>10^{-12}</math> grams.

===Comparison with the sizes of protein and phospholipids (the constituents of the membranes surrounding it) (within one order of magnitude apart)===

The intermembrane space is the space between two [[biological membrane]]s: the [[inner mitochondrial membrane]] and the [[outer mitochondrial membrane]]. Each of these is a [[lipid bilayer]] with [[membrane protein]]s, including membrane proteins that are partly or wholly on the intermembrane space side. (Any [[membrane transport protein]] -- any protein that transports stuff across the membranes -- must be a [[transmembrane protein]] and hence be on both sides).

To get a better sense of the thickness of the intermembrane space, therefore, it makes sense to compare this with the size of phospholipids (the stuff the lipid bilayer is made of) and proteins (in general, and the particular ones found in the IMS).

* Lipid bilayers are in the 3-7 nm range.
* Protein diameters can vary between 2 nm and 12 nm, with most proteins in the 2-6 nm range. Not all of this protein diameter would be on the IMS side though; for the transmembrane proteins, some of the protein would be on the other side.

Overall, the thickness of the IMS is about 3 to 10 times the range of thicknesses for the membranes and membrane proteins. A visual analogy here might be to think (locally) of the IMS as a corridor and the lipid bilayers of the inner and outer mitochondrial membranes as the walls on the two sides of the corridor, with the proteins being the doors. This analogy helps give a rough sense of the relative scales.

==Chemical composition==

===Number of hydrogen ions===

NOTE: In practice, hydrogen ions are rarely floating freely -- they are usually bound to at least one water molecule, forming a hydronium ion. For ease of discourse, we say "hydrogen ion"; the term "proton" may also be used, but it's important to keep in mind that this is referring to single-proton atomic nuclei, not to protons that exist in larger atomic nuclei.

The pH of the IMS ranges between 7.0 and 7.4. In other words, it's a little more alkaline than neutral pH (at human body temperature, neutral pH is about 6.8). Combining this with the size calculation, we can estimate the number of protons (hydrogen ions) in the IMS.

At the upper end would be the case of a pH of 7.0. That means that there are <math>10^{-7}</math> moles of hydrogen per liter. Our upper estimate for IMS volume is <math>0.62 fL = 0.62 * 10^{-15} L</math>, which gives a total of <math>0.62 * 10^{-22}</math> moles of hydrogen ions in the IMS. 1 mole of something is <math>6.023 * 10^{23}</math> many of that, so plugging that in, we get:

<math>0.62 * 10^{-22} * 6.023 * 10^{23} = 37.34</math>

So we get a grand total of 37.34 hydrogen ions in the IMS! That's not a lot of hydrogen ions. Obviously, the numbers here are all approximations -- the actual number of ions at any given time should be an integer. But note that this is using the high-end estimates, so at the lower end of the range, we have even fewer hydrogen ions. Overall, we expect a single-digit or double-digit number of hydrogen ions in the IMS.

The IMS has the ability to freely exchange hydrogen ions across the [[outer mitochondrial membrane]] with both its neighbor mitochondria (the adjacent nodes to it in the [[mitochondrial network]]) and the cytosol. Thus, even though the number of hydrogen ions in a single IMS may seem too small to be stable, the ability to exchange hydrogen ions means there is a bit more stability in numbers. Relatedly, it's worth noting that the cytosolic pH is at the high end (about 7.4). Therefore, protons would be expected to diffuse out from the IMS into the much bigger cytosol, eventually causing the IMS to get to a pH of 4. The reason this doesn't usually happen, and the IMS is able to maintain a slightly lower pH (higher concentration of hydrogen ions) than the surrounding cytosol is the pumping of protons from the mitochondrial matrix across the inner mitochondrial membrane.

===Other small molecules===

As the outer mitochondrial membrane is freely permeable to small molecules, the intermembrane space can be thought of as being contiguous with the cytosol as far as small molecules are concerned. In particular, the concentration of each molecule in the IMS is expected to roughly match the concentration in the cytosol. Hydrogen ions, as discussed in the preceding section, are a partial exception, insofar as the IMS has somewhat higher concentration of hydrogen ions due to receiving these ions regularly from the mitochondrial matrix.

The IMS can differ quite a bit from the mitochondrial matrix, since the inner mitochondrial membrane, that separates the two, is extremely selective.

Example calculation: in human cells, cellular potassium concentration is about 150 mmol/L. With a volume of <math>0.62 * 10^{-15} L</math>, that works out to:

<math>0.62 * 10^{-15} * 150 * 10^{-3} * 6.023 * 10^{23} = 56013900</math>

That's about 56 million potassium ions. It's a lot more than hydrogen ions, which is as expected from the fact that there's a million-fold concentration difference.

===Proteins===

Large molecules, such as proteins, cannot freely move through the outer mitochondrial membrane. So, the protein composition of the IMS can (and does) differ from that of the cytosol. It also differs from the protein composition of the mitochondrial matrix, as proteins are not freely transported across the inner mitochondrial membrane.

The intermembrane space cannot ''make'' its own protein, so the protein it does get it must get from the cytosol, and it can get only those proteins from the cytosol that the outer mitochondrial membrane allows.

The determination of what proteins are allowed is itself done by complexes of [[membrane transport protein]]s (these are [[transmembrane protein]]s that help transport stuff across the membrane):

* The [[translocase of the outer membrane]] (TOM) complex is a complex of membrane transport proteins on the outer mitochondrial membrane that control what proteins are allowed to move across the outer mitochondrial membrane (between the cytosol and the intermembrane space).
* The [[translocase of the inner membrane]] (TIM) complex is a complex of membrane transport proteins on the inner mitochondrial membrane that control what proteins are allowed to move across the inner mitochondrial membrane (between the intermembrane space and mitochondrial matrix).

Together, these complexes control the protein composition of the intermembrane space. The TOM complex determines what gets in from the cytosol outside, and the TIM complex determines what of it goes into the mitochondrial matrix.

Perimitochondrial space

2024-10-28T05:46:56Z

Vipul: Redirected page to Intermembrane space of mitochondrion

#redirect [[Intermembrane space of mitochondrion]]

Intermembrane space of mitochondrion

2024-10-28T05:44:58Z

Vipul: /* Other small molecules */

{{component of organelle|mitochondrion}}

==Definition==

The '''intermembrane space of mitochondrion''' ('''IMS''') is a space between the two membranes of a [[mitochondrion]]: the [[outer mitochondrial membrane]] (bounding it on the outside, and separating it from the [[cytosol]] or adjacent mitochondria in the [[mitochondrial network]]) and [[inner mitochondrial membrane]] (bounding it on the inside, and separating it from the [[mitochondrial matrix]]).

==Summary==

{| class="sortable" border="1"
! Item !! Value
|-
| Type of organisms whose cells contain the intermembrane space || Same as the organisms whose cells contain mitochondria: [[eukaryotic cell]]s ''only'', including [[plant cell]]s, [[animal cell]]s, and the cells of [[protist]]s and [[fungus|fungi]]
|-
| Type of cells within the organisms that contain the intermembrane space || Same as the cells that contain mitochondria: all cells except [[red blood cell]]s in [[mammal]]s (other vertebrates ''do'' have mitochondria in their red blood cells).
|-
| Number of intermembrane spaces per cell || Same as the number of mitochondria: 1 to 1000s, depending on the energy needs of the cell
|-
| Size || <math>~200</math> angstrom or <math>~20 nm</math> thickness (very approximate), accounting for less than 5% of the length (less than 10% even if you consider that it's on both sides).
|-
| Location within the mitochondrion || It is right inside of the boundary of the mitochondrion (the boundary is the [[outer mitochondrial membrane]]).
|-
| What's on both sides of it || Inside: [[inner mitochondrial membrane]] (separating it from the [[mitochondrial matrix]]), outside: [[outer mitochondrial membrane]] (separating it from the [[cytosol]] or adjacent mitochondria in the [[mitochondrial network]])
|-
| Structural components || The ''intracristal space'' is the part of the intermembrane space between the folds (cristae) of the inner mitochondrial membrane. The ''peripheral space'' is the part of the intermembrane space farther out of the inner mitochondrial membrane.
|-
| pH || About 7.0 to 7.4. Although still a little alkaline, it is less so than the mitochondrial matrix and less so than the rest of the cell, due to the pumping out of protons from the mitochondrial matrix as part of the [[electron transport chain]].
|}

==Size and shape==

===Limitations of study===

Unlike the [[mitochondrion]] as a whole, the intermembrane space of mitochondrion is too small to be seen with a light microscope. The electron microscope that is necessary to see it can be destructive to the living cell and may change the shape of the mitochondrion.

===Shape===

The entire mitochondrion (bounded by the [[outer mitochondrial membrane]]) can be approximated as a rounded cylinder (cylinder with rounded edges) and the mitochondrial matrix (bounded by the [[inner mitochondrial membrane]]) can be approximated as a rounded cylinder that is fully inside it. The intermembrane space is the region that's in the bigger rounded cylinder and outside the smaller rounded cylinder, and its thickness (up to 20 nm) represents the margin around the smaller cylinder.

This crude description captures the concept of the peripheral intermembrane space. The intracristal space is a bunch of little crevices in the inner cylinder.

===Size and volume calculation===

We use this size range for the mitochondrion:

* The length is generally at least 1 <math>\mu m</math> and at most 4 <math>\mu m</math>.
* The tubular radius is generally at least 0.5 <math>\mu m</math> and at most 1 <math>\mu m</math>.

We also use that the thickness of the intermembrane space is about 20 <math>nm</math>.

Illustratively, and using the biggest size estimates, let's say the mitochondrion has a length of 4 <math>\mu m</math>, a tubular radius of 1 <math>\mu m</math>, and an intermembrane space that is uniformly 20 <math>nm</math> thickness. Let's model the mitochondrion and mitochondrial matrix as cylinders.

* Volume of the mitochondrion is <math>\pi r^2 h</math> where <math>r = 1 \mu m, h = 4 \mu m</math>, giving <math>12.57 \mu m^3</math>
* Volume of the mitochondrial matrix (the inner cylinder) is <math>\pi r^2 h</math> where <math>r = 0.98 \mu m, h =3.96 \mu m</math> (these values are obtained by subtracting the thickness of the IMS from the radius and twice the thickness of the IMS from the height), giving <math>11.95 \mu m^3</math>. The difference is <math>0.62 \mu m^3</math>.

A cubic micrometer (<math>\mu m^3</math>) is the same as a femtoliter, or <math>10^{-15}</math> liters. So the volume of the intermembrane space works out to be <math>0.62 fL</math>. But this is the upper end. The lower end would be roughly about 1/16 of this, or about <math>0.04 fL</math>.

Note that this calculation is most faithful for the peripheral IMS. The intercristal IMS is not covered here, but likely does not cover much volume (its significance is more in terms of the high surface area that it covers, not the volume).

===Mass===

Since [[most cellular matter is approximately as dense as water]], we can approximate the density of the intermembrane space using the density of water, which is about 1 gram per milliliter. Based on the volume estimate above, we get that the mass of a mitochondrion is approximately between 0.04 and 0.62 picograms, where a picogram is <math>10^{-12}</math> grams.

===Comparison with the sizes of protein and phospholipids (the constituents of the membranes surrounding it) (within one order of magnitude apart)===

The intermembrane space is the space between two [[biological membrane]]s: the [[inner mitochondrial membrane]] and the [[outer mitochondrial membrane]]. Each of these is a [[lipid bilayer]] with [[membrane protein]]s, including membrane proteins that are partly or wholly on the intermembrane space side. (Any [[membrane transport protein]] -- any protein that transports stuff across the membranes -- must be a [[transmembrane protein]] and hence be on both sides).

To get a better sense of the thickness of the intermembrane space, therefore, it makes sense to compare this with the size of phospholipids (the stuff the lipid bilayer is made of) and proteins (in general, and the particular ones found in the IMS).

* Lipid bilayers are in the 3-7 nm range.
* Protein diameters can vary between 2 nm and 12 nm, with most proteins in the 2-6 nm range. Not all of this protein diameter would be on the IMS side though; for the transmembrane proteins, some of the protein would be on the other side.

Overall, the thickness of the IMS is about 3 to 10 times the range of thicknesses for the membranes and membrane proteins. A visual analogy here might be to think (locally) of the IMS as a corridor and the lipid bilayers of the inner and outer mitochondrial membranes as the walls on the two sides of the corridor, with the proteins being the doors. This analogy helps give a rough sense of the relative scales.

==Chemical composition==

===Number of hydrogen ions===

NOTE: In practice, hydrogen ions are rarely floating freely -- they are usually bound to at least one water molecule, forming a hydronium ion. For ease of discourse, we say "hydrogen ion"; the term "proton" may also be used, but it's important to keep in mind that this is referring to single-proton atomic nuclei, not to protons that exist in larger atomic nuclei.

The pH of the IMS ranges between 7.0 and 7.4. In other words, it's a little more alkaline than neutral pH (at human body temperature, neutral pH is about 6.8). Combining this with the size calculation, we can estimate the number of protons (hydrogen ions) in the IMS.

At the upper end would be the case of a pH of 7.0. That means that there are <math>10^{-7}</math> moles of hydrogen per liter. Our upper estimate for IMS volume is <math>0.62 fL = 0.62 * 10^{-15} L</math>, which gives a total of <math>0.62 * 10^{-22}</math> moles of hydrogen ions in the IMS. 1 mole of something is <math>6.023 * 10^{23}</math> many of that, so plugging that in, we get:

<math>0.62 * 10^{-22} * 6.023 * 10^{23} = 37.34</math>

So we get a grand total of 37.34 hydrogen ions in the IMS! That's not a lot of hydrogen ions. Obviously, the numbers here are all approximations -- the actual number of ions at any given time should be an integer. But note that this is using the high-end estimates, so at the lower end of the range, we have even fewer hydrogen ions. Overall, we expect a single-digit or double-digit number of hydrogen ions in the IMS.

The IMS has the ability to freely exchange hydrogen ions across the [[outer mitochondrial membrane]] with both its neighbor mitochondria (the adjacent nodes to it in the [[mitochondrial network]]) and the cytosol. Thus, even though the number of hydrogen ions in a single IMS may seem too small to be stable, the ability to exchange hydrogen ions means there is a bit more stability in numbers. Relatedly, it's worth noting that the cytosolic pH is at the high end (about 7.4). Therefore, protons would be expected to diffuse out from the IMS into the much bigger cytosol, eventually causing the IMS to get to a pH of 4. The reason this doesn't usually happen, and the IMS is able to maintain a slightly lower pH (higher concentration of hydrogen ions) than the surrounding cytosol is the pumping of protons from the mitochondrial matrix across the inner mitochondrial membrane.

===Other small molecules===

As the outer mitochondrial membrane is freely permeable to small molecules, the intermembrane space can be thought of as being contiguous with the cytosol as far as small molecules are concerned. In particular, the concentration of each molecule in the IMS is expected to roughly match the concentration in the cytosol. Hydrogen ions, as discussed in the preceding section, are a partial exception, insofar as the IMS has somewhat higher concentration of hydrogen ions due to receiving these ions regularly from the mitochondrial matrix.

The IMS can differ quite a bit from the mitochondrial matrix, since the inner mitochondrial membrane, that separates the two, is extremely selective.

Example calculation: in human cells, cellular potassium concentration is about 150 mmol/L. With a volume of <math>0.62 * 10^{-15} L</math>, that works out to:

<math>0.62 * 10^{-15} * 150 * 10^{-3} * 6.023 * 10^{23} = 56013900</math>

That's about 56 million potassium ions. It's a lot more than hydrogen ions, which is as expected from the fact that there's a million-fold concentration difference.

===Proteins===

Large molecules, such as proteins, cannot freely move through the outer mitochondrial membrane. So, the protein composition of the IMS can (and does) differ from that of the cytosol. It also differs from the protein composition of the mitochondrial matrix, as proteins are not freely transported across the inner mitochondrial membrane.

The intermembrane space cannot ''make'' its own protein, so the protein it does get it must get from the cytosol, and it can get only those proteins from the cytosol that the outer mitochondrial membrane allows.

The determination of what proteins are allowed is itself done by complexes of [[membrane transport protein]]s (these are [[transmembrane protein]]s that help transport stuff across the membrane):

* The [[translocase of the outer membrane]] (TOM) complex is a complex of membrane transport proteins on the outer mitochondrial membrane that control what proteins are allowed to move across the outer mitochondrial membrane (between the cytosol and the intermembrane space).
* The [[translocase of the inner membrane]] (TIM) complex is a complex of membrane transport proteins on the inner mitochondrial membrane that control what proteins are allowed to move across the inner mitochondrial membrane (between the intermembrane space and mitochondrial matrix).

Together, these complexes control the protein composition of the intermembrane space. The TOM complex determines what gets in from the cytosol outside, and the TIM complex determines what of it goes into the mitochondrial matrix.

Intermembrane space of mitochondrion

2024-10-28T05:40:59Z

Vipul: /* Proteins */

{{component of organelle|mitochondrion}}

==Definition==

The '''intermembrane space of mitochondrion''' ('''IMS''') is a space between the two membranes of a [[mitochondrion]]: the [[outer mitochondrial membrane]] (bounding it on the outside, and separating it from the [[cytosol]] or adjacent mitochondria in the [[mitochondrial network]]) and [[inner mitochondrial membrane]] (bounding it on the inside, and separating it from the [[mitochondrial matrix]]).

==Summary==

{| class="sortable" border="1"
! Item !! Value
|-
| Type of organisms whose cells contain the intermembrane space || Same as the organisms whose cells contain mitochondria: [[eukaryotic cell]]s ''only'', including [[plant cell]]s, [[animal cell]]s, and the cells of [[protist]]s and [[fungus|fungi]]
|-
| Type of cells within the organisms that contain the intermembrane space || Same as the cells that contain mitochondria: all cells except [[red blood cell]]s in [[mammal]]s (other vertebrates ''do'' have mitochondria in their red blood cells).
|-
| Number of intermembrane spaces per cell || Same as the number of mitochondria: 1 to 1000s, depending on the energy needs of the cell
|-
| Size || <math>~200</math> angstrom or <math>~20 nm</math> thickness (very approximate), accounting for less than 5% of the length (less than 10% even if you consider that it's on both sides).
|-
| Location within the mitochondrion || It is right inside of the boundary of the mitochondrion (the boundary is the [[outer mitochondrial membrane]]).
|-
| What's on both sides of it || Inside: [[inner mitochondrial membrane]] (separating it from the [[mitochondrial matrix]]), outside: [[outer mitochondrial membrane]] (separating it from the [[cytosol]] or adjacent mitochondria in the [[mitochondrial network]])
|-
| Structural components || The ''intracristal space'' is the part of the intermembrane space between the folds (cristae) of the inner mitochondrial membrane. The ''peripheral space'' is the part of the intermembrane space farther out of the inner mitochondrial membrane.
|-
| pH || About 7.0 to 7.4. Although still a little alkaline, it is less so than the mitochondrial matrix and less so than the rest of the cell, due to the pumping out of protons from the mitochondrial matrix as part of the [[electron transport chain]].
|}

==Size and shape==

===Limitations of study===

Unlike the [[mitochondrion]] as a whole, the intermembrane space of mitochondrion is too small to be seen with a light microscope. The electron microscope that is necessary to see it can be destructive to the living cell and may change the shape of the mitochondrion.

===Shape===

The entire mitochondrion (bounded by the [[outer mitochondrial membrane]]) can be approximated as a rounded cylinder (cylinder with rounded edges) and the mitochondrial matrix (bounded by the [[inner mitochondrial membrane]]) can be approximated as a rounded cylinder that is fully inside it. The intermembrane space is the region that's in the bigger rounded cylinder and outside the smaller rounded cylinder, and its thickness (up to 20 nm) represents the margin around the smaller cylinder.

This crude description captures the concept of the peripheral intermembrane space. The intracristal space is a bunch of little crevices in the inner cylinder.

===Size and volume calculation===

We use this size range for the mitochondrion:

* The length is generally at least 1 <math>\mu m</math> and at most 4 <math>\mu m</math>.
* The tubular radius is generally at least 0.5 <math>\mu m</math> and at most 1 <math>\mu m</math>.

We also use that the thickness of the intermembrane space is about 20 <math>nm</math>.

Illustratively, and using the biggest size estimates, let's say the mitochondrion has a length of 4 <math>\mu m</math>, a tubular radius of 1 <math>\mu m</math>, and an intermembrane space that is uniformly 20 <math>nm</math> thickness. Let's model the mitochondrion and mitochondrial matrix as cylinders.

* Volume of the mitochondrion is <math>\pi r^2 h</math> where <math>r = 1 \mu m, h = 4 \mu m</math>, giving <math>12.57 \mu m^3</math>
* Volume of the mitochondrial matrix (the inner cylinder) is <math>\pi r^2 h</math> where <math>r = 0.98 \mu m, h =3.96 \mu m</math> (these values are obtained by subtracting the thickness of the IMS from the radius and twice the thickness of the IMS from the height), giving <math>11.95 \mu m^3</math>. The difference is <math>0.62 \mu m^3</math>.

A cubic micrometer (<math>\mu m^3</math>) is the same as a femtoliter, or <math>10^{-15}</math> liters. So the volume of the intermembrane space works out to be <math>0.62 fL</math>. But this is the upper end. The lower end would be roughly about 1/16 of this, or about <math>0.04 fL</math>.

Note that this calculation is most faithful for the peripheral IMS. The intercristal IMS is not covered here, but likely does not cover much volume (its significance is more in terms of the high surface area that it covers, not the volume).

===Mass===

Since [[most cellular matter is approximately as dense as water]], we can approximate the density of the intermembrane space using the density of water, which is about 1 gram per milliliter. Based on the volume estimate above, we get that the mass of a mitochondrion is approximately between 0.04 and 0.62 picograms, where a picogram is <math>10^{-12}</math> grams.

===Comparison with the sizes of protein and phospholipids (the constituents of the membranes surrounding it) (within one order of magnitude apart)===

The intermembrane space is the space between two [[biological membrane]]s: the [[inner mitochondrial membrane]] and the [[outer mitochondrial membrane]]. Each of these is a [[lipid bilayer]] with [[membrane protein]]s, including membrane proteins that are partly or wholly on the intermembrane space side. (Any [[membrane transport protein]] -- any protein that transports stuff across the membranes -- must be a [[transmembrane protein]] and hence be on both sides).

To get a better sense of the thickness of the intermembrane space, therefore, it makes sense to compare this with the size of phospholipids (the stuff the lipid bilayer is made of) and proteins (in general, and the particular ones found in the IMS).

* Lipid bilayers are in the 3-7 nm range.
* Protein diameters can vary between 2 nm and 12 nm, with most proteins in the 2-6 nm range. Not all of this protein diameter would be on the IMS side though; for the transmembrane proteins, some of the protein would be on the other side.

Overall, the thickness of the IMS is about 3 to 10 times the range of thicknesses for the membranes and membrane proteins. A visual analogy here might be to think (locally) of the IMS as a corridor and the lipid bilayers of the inner and outer mitochondrial membranes as the walls on the two sides of the corridor, with the proteins being the doors. This analogy helps give a rough sense of the relative scales.

==Chemical composition==

===Number of hydrogen ions===

NOTE: In practice, hydrogen ions are rarely floating freely -- they are usually bound to at least one water molecule, forming a hydronium ion. For ease of discourse, we say "hydrogen ion"; the term "proton" may also be used, but it's important to keep in mind that this is referring to single-proton atomic nuclei, not to protons that exist in larger atomic nuclei.

The pH of the IMS ranges between 7.0 and 7.4. In other words, it's a little more alkaline than neutral pH (at human body temperature, neutral pH is about 6.8). Combining this with the size calculation, we can estimate the number of protons (hydrogen ions) in the IMS.

At the upper end would be the case of a pH of 7.0. That means that there are <math>10^{-7}</math> moles of hydrogen per liter. Our upper estimate for IMS volume is <math>0.62 fL = 0.62 * 10^{-15} L</math>, which gives a total of <math>0.62 * 10^{-22}</math> moles of hydrogen ions in the IMS. 1 mole of something is <math>6.023 * 10^{23}</math> many of that, so plugging that in, we get:

<math>0.62 * 10^{-22} * 6.023 * 10^{23} = 37.34</math>

So we get a grand total of 37.34 hydrogen ions in the IMS! That's not a lot of hydrogen ions. Obviously, the numbers here are all approximations -- the actual number of ions at any given time should be an integer. But note that this is using the high-end estimates, so at the lower end of the range, we have even fewer hydrogen ions. Overall, we expect a single-digit or double-digit number of hydrogen ions in the IMS.

The IMS has the ability to freely exchange hydrogen ions across the [[outer mitochondrial membrane]] with both its neighbor mitochondria (the adjacent nodes to it in the [[mitochondrial network]]) and the cytosol. Thus, even though the number of hydrogen ions in a single IMS may seem too small to be stable, the ability to exchange hydrogen ions means there is a bit more stability in numbers. Relatedly, it's worth noting that the cytosolic pH is at the high end (about 7.4). Therefore, protons would be expected to diffuse out from the IMS into the much bigger cytosol, eventually causing the IMS to get to a pH of 4. The reason this doesn't usually happen, and the IMS is able to maintain a slightly lower pH (higher concentration of hydrogen ions) than the surrounding cytosol is the pumping of protons from the mitochondrial matrix across the inner mitochondrial membrane.

===Other small molecules===

As the outer mitochondrial membrane is freely permeable to small molecules, the intermembrane space can be thought of as being contiguous with the cytosol as far as small molecules are concerned. In particular, the concentration of each molecule in the IMS is expected to roughly match the concentration in the cytosol. Hydrogen ions, as discussed in the preceding section, are a partial exception, insofar as the IMS has somewhat higher concentration of hydrogen ions due to receiving these ions regularly from the mitochondrial matrix.

The IMS can differ quite a bit from the mitochondrial matrix, since the inner mitochondrial membrane, that separates the two, is extremely selective.

===Proteins===

Large molecules, such as proteins, cannot freely move through the outer mitochondrial membrane. So, the protein composition of the IMS can (and does) differ from that of the cytosol. It also differs from the protein composition of the mitochondrial matrix, as proteins are not freely transported across the inner mitochondrial membrane.

The intermembrane space cannot ''make'' its own protein, so the protein it does get it must get from the cytosol, and it can get only those proteins from the cytosol that the outer mitochondrial membrane allows.

The determination of what proteins are allowed is itself done by complexes of [[membrane transport protein]]s (these are [[transmembrane protein]]s that help transport stuff across the membrane):

* The [[translocase of the outer membrane]] (TOM) complex is a complex of membrane transport proteins on the outer mitochondrial membrane that control what proteins are allowed to move across the outer mitochondrial membrane (between the cytosol and the intermembrane space).
* The [[translocase of the inner membrane]] (TIM) complex is a complex of membrane transport proteins on the inner mitochondrial membrane that control what proteins are allowed to move across the inner mitochondrial membrane (between the intermembrane space and mitochondrial matrix).

Together, these complexes control the protein composition of the intermembrane space. The TOM complex determines what gets in from the cytosol outside, and the TIM complex determines what of it goes into the mitochondrial matrix.

Intermembrane space of mitochondrion

2024-10-28T05:33:49Z

Vipul: /* Size and shape */

{{component of organelle|mitochondrion}}

==Definition==

The '''intermembrane space of mitochondrion''' ('''IMS''') is a space between the two membranes of a [[mitochondrion]]: the [[outer mitochondrial membrane]] (bounding it on the outside, and separating it from the [[cytosol]] or adjacent mitochondria in the [[mitochondrial network]]) and [[inner mitochondrial membrane]] (bounding it on the inside, and separating it from the [[mitochondrial matrix]]).

==Summary==

{| class="sortable" border="1"
! Item !! Value
|-
| Type of organisms whose cells contain the intermembrane space || Same as the organisms whose cells contain mitochondria: [[eukaryotic cell]]s ''only'', including [[plant cell]]s, [[animal cell]]s, and the cells of [[protist]]s and [[fungus|fungi]]
|-
| Type of cells within the organisms that contain the intermembrane space || Same as the cells that contain mitochondria: all cells except [[red blood cell]]s in [[mammal]]s (other vertebrates ''do'' have mitochondria in their red blood cells).
|-
| Number of intermembrane spaces per cell || Same as the number of mitochondria: 1 to 1000s, depending on the energy needs of the cell
|-
| Size || <math>~200</math> angstrom or <math>~20 nm</math> thickness (very approximate), accounting for less than 5% of the length (less than 10% even if you consider that it's on both sides).
|-
| Location within the mitochondrion || It is right inside of the boundary of the mitochondrion (the boundary is the [[outer mitochondrial membrane]]).
|-
| What's on both sides of it || Inside: [[inner mitochondrial membrane]] (separating it from the [[mitochondrial matrix]]), outside: [[outer mitochondrial membrane]] (separating it from the [[cytosol]] or adjacent mitochondria in the [[mitochondrial network]])
|-
| Structural components || The ''intracristal space'' is the part of the intermembrane space between the folds (cristae) of the inner mitochondrial membrane. The ''peripheral space'' is the part of the intermembrane space farther out of the inner mitochondrial membrane.
|-
| pH || About 7.0 to 7.4. Although still a little alkaline, it is less so than the mitochondrial matrix and less so than the rest of the cell, due to the pumping out of protons from the mitochondrial matrix as part of the [[electron transport chain]].
|}

==Size and shape==

===Limitations of study===

Unlike the [[mitochondrion]] as a whole, the intermembrane space of mitochondrion is too small to be seen with a light microscope. The electron microscope that is necessary to see it can be destructive to the living cell and may change the shape of the mitochondrion.

===Shape===

The entire mitochondrion (bounded by the [[outer mitochondrial membrane]]) can be approximated as a rounded cylinder (cylinder with rounded edges) and the mitochondrial matrix (bounded by the [[inner mitochondrial membrane]]) can be approximated as a rounded cylinder that is fully inside it. The intermembrane space is the region that's in the bigger rounded cylinder and outside the smaller rounded cylinder, and its thickness (up to 20 nm) represents the margin around the smaller cylinder.

This crude description captures the concept of the peripheral intermembrane space. The intracristal space is a bunch of little crevices in the inner cylinder.

===Size and volume calculation===

We use this size range for the mitochondrion:

* The length is generally at least 1 <math>\mu m</math> and at most 4 <math>\mu m</math>.
* The tubular radius is generally at least 0.5 <math>\mu m</math> and at most 1 <math>\mu m</math>.

We also use that the thickness of the intermembrane space is about 20 <math>nm</math>.

Illustratively, and using the biggest size estimates, let's say the mitochondrion has a length of 4 <math>\mu m</math>, a tubular radius of 1 <math>\mu m</math>, and an intermembrane space that is uniformly 20 <math>nm</math> thickness. Let's model the mitochondrion and mitochondrial matrix as cylinders.

* Volume of the mitochondrion is <math>\pi r^2 h</math> where <math>r = 1 \mu m, h = 4 \mu m</math>, giving <math>12.57 \mu m^3</math>
* Volume of the mitochondrial matrix (the inner cylinder) is <math>\pi r^2 h</math> where <math>r = 0.98 \mu m, h =3.96 \mu m</math> (these values are obtained by subtracting the thickness of the IMS from the radius and twice the thickness of the IMS from the height), giving <math>11.95 \mu m^3</math>. The difference is <math>0.62 \mu m^3</math>.

A cubic micrometer (<math>\mu m^3</math>) is the same as a femtoliter, or <math>10^{-15}</math> liters. So the volume of the intermembrane space works out to be <math>0.62 fL</math>. But this is the upper end. The lower end would be roughly about 1/16 of this, or about <math>0.04 fL</math>.

Note that this calculation is most faithful for the peripheral IMS. The intercristal IMS is not covered here, but likely does not cover much volume (its significance is more in terms of the high surface area that it covers, not the volume).

===Mass===

Since [[most cellular matter is approximately as dense as water]], we can approximate the density of the intermembrane space using the density of water, which is about 1 gram per milliliter. Based on the volume estimate above, we get that the mass of a mitochondrion is approximately between 0.04 and 0.62 picograms, where a picogram is <math>10^{-12}</math> grams.

===Comparison with the sizes of protein and phospholipids (the constituents of the membranes surrounding it) (within one order of magnitude apart)===

The intermembrane space is the space between two [[biological membrane]]s: the [[inner mitochondrial membrane]] and the [[outer mitochondrial membrane]]. Each of these is a [[lipid bilayer]] with [[membrane protein]]s, including membrane proteins that are partly or wholly on the intermembrane space side. (Any [[membrane transport protein]] -- any protein that transports stuff across the membranes -- must be a [[transmembrane protein]] and hence be on both sides).

To get a better sense of the thickness of the intermembrane space, therefore, it makes sense to compare this with the size of phospholipids (the stuff the lipid bilayer is made of) and proteins (in general, and the particular ones found in the IMS).

* Lipid bilayers are in the 3-7 nm range.
* Protein diameters can vary between 2 nm and 12 nm, with most proteins in the 2-6 nm range. Not all of this protein diameter would be on the IMS side though; for the transmembrane proteins, some of the protein would be on the other side.

Overall, the thickness of the IMS is about 3 to 10 times the range of thicknesses for the membranes and membrane proteins. A visual analogy here might be to think (locally) of the IMS as a corridor and the lipid bilayers of the inner and outer mitochondrial membranes as the walls on the two sides of the corridor, with the proteins being the doors. This analogy helps give a rough sense of the relative scales.

==Chemical composition==

===Number of hydrogen ions===

NOTE: In practice, hydrogen ions are rarely floating freely -- they are usually bound to at least one water molecule, forming a hydronium ion. For ease of discourse, we say "hydrogen ion"; the term "proton" may also be used, but it's important to keep in mind that this is referring to single-proton atomic nuclei, not to protons that exist in larger atomic nuclei.

The pH of the IMS ranges between 7.0 and 7.4. In other words, it's a little more alkaline than neutral pH (at human body temperature, neutral pH is about 6.8). Combining this with the size calculation, we can estimate the number of protons (hydrogen ions) in the IMS.

At the upper end would be the case of a pH of 7.0. That means that there are <math>10^{-7}</math> moles of hydrogen per liter. Our upper estimate for IMS volume is <math>0.62 fL = 0.62 * 10^{-15} L</math>, which gives a total of <math>0.62 * 10^{-22}</math> moles of hydrogen ions in the IMS. 1 mole of something is <math>6.023 * 10^{23}</math> many of that, so plugging that in, we get:

<math>0.62 * 10^{-22} * 6.023 * 10^{23} = 37.34</math>

So we get a grand total of 37.34 hydrogen ions in the IMS! That's not a lot of hydrogen ions. Obviously, the numbers here are all approximations -- the actual number of ions at any given time should be an integer. But note that this is using the high-end estimates, so at the lower end of the range, we have even fewer hydrogen ions. Overall, we expect a single-digit or double-digit number of hydrogen ions in the IMS.

The IMS has the ability to freely exchange hydrogen ions across the [[outer mitochondrial membrane]] with both its neighbor mitochondria (the adjacent nodes to it in the [[mitochondrial network]]) and the cytosol. Thus, even though the number of hydrogen ions in a single IMS may seem too small to be stable, the ability to exchange hydrogen ions means there is a bit more stability in numbers. Relatedly, it's worth noting that the cytosolic pH is at the high end (about 7.4). Therefore, protons would be expected to diffuse out from the IMS into the much bigger cytosol, eventually causing the IMS to get to a pH of 4. The reason this doesn't usually happen, and the IMS is able to maintain a slightly lower pH (higher concentration of hydrogen ions) than the surrounding cytosol is the pumping of protons from the mitochondrial matrix across the inner mitochondrial membrane.

===Other small molecules===

As the outer mitochondrial membrane is freely permeable to small molecules, the intermembrane space can be thought of as being contiguous with the cytosol as far as small molecules are concerned. In particular, the concentration of each molecule in the IMS is expected to roughly match the concentration in the cytosol. Hydrogen ions, as discussed in the preceding section, are a partial exception, insofar as the IMS has somewhat higher concentration of hydrogen ions due to receiving these ions regularly from the mitochondrial matrix.

The IMS can differ quite a bit from the mitochondrial matrix, since the inner mitochondrial membrane, that separates the two, is extremely selective.

===Proteins===

Large molecules, such as proteins, cannot freely move through the outer mitochondrial membrane. So, the protein composition of the IMS can (and does) differ from that of the cytosol. It also differs from the protein composition of the mitochondrial matrix, as proteins are not freely transported across the inner mitochondrial membrane.

The intermembrane space cannot ''make'' its own protein, so the protein it does get it must get from the cytosol, and it can get only those proteins from the cytosol that the outer mitochondrial membrane allows.

Integral membrane protein

2024-10-28T05:21:31Z

Vipul: /* Relation with other concepts */

==Definition==

An '''integral membrane protein''' (also called '''IMP''') is a [[protein]] molecule permanently attached to a [[biological membrane]] (such as a [[cell membrane]] or the membrane of an [[organelle]] in a [[eukaryotic cell]]).

==Types==

Integral membrane proteins are of two main types:

# [[transmembrane protein]] (also called integral polytopic protein)
# [[integral monotopic protein]]

==Relation with other concepts==

===Broader concepts===

{| class="sortable" border="1"
! Concept !! Meaning !! Relationship with the concept of integral membrane protein !! Intermediate notions
|-
| [[Narrower than::membrane protein]] || protein that interacts with a biological membrane, but not necessarily attached to it || integral membrane proteins are a special kind of membrane protein that is permanently attached to the membrane; the other kind are [[peripheral membrane protein]]s || {{intermediate notions short|integral membrane protein|membrane protein}}
|}

===Narrower concepts===

{| class="sortable" border="1"
! Concept !! Meaning !! Relationship with the concept of integral membrane protein !! Intermediate notions
|-
| [[Broader than::transmembrane protein]] || protein that is attached to both sides of the [[lipid bilayer]] of the biological membrane || transmembrane proteins are one kind of integral membrane protein (the ''polytopic'' type); the other type is [[integral monotopic protein]]s, that are attached to just one side || {{intermediate notions short|transmembrane protein|integral membrane protein}}
|-
| [[Broader than::membrane transport protein]] || protein that facilitates transport across the biological membrane || (via transmembrane protein) || {{intermediate notions short|membrane transport protein|integral membrane protein}}
|}

Intermembrane space of mitochondrion

2024-10-28T05:20:16Z

Vipul: /* Chemical composition */

{{component of organelle|mitochondrion}}

==Definition==

The '''intermembrane space of mitochondrion''' ('''IMS''') is a space between the two membranes of a [[mitochondrion]]: the [[outer mitochondrial membrane]] (bounding it on the outside, and separating it from the [[cytosol]] or adjacent mitochondria in the [[mitochondrial network]]) and [[inner mitochondrial membrane]] (bounding it on the inside, and separating it from the [[mitochondrial matrix]]).

==Summary==

{| class="sortable" border="1"
! Item !! Value
|-
| Type of organisms whose cells contain the intermembrane space || Same as the organisms whose cells contain mitochondria: [[eukaryotic cell]]s ''only'', including [[plant cell]]s, [[animal cell]]s, and the cells of [[protist]]s and [[fungus|fungi]]
|-
| Type of cells within the organisms that contain the intermembrane space || Same as the cells that contain mitochondria: all cells except [[red blood cell]]s in [[mammal]]s (other vertebrates ''do'' have mitochondria in their red blood cells).
|-
| Number of intermembrane spaces per cell || Same as the number of mitochondria: 1 to 1000s, depending on the energy needs of the cell
|-
| Size || <math>~200</math> angstrom or <math>~20 nm</math> thickness (very approximate), accounting for less than 5% of the length (less than 10% even if you consider that it's on both sides).
|-
| Location within the mitochondrion || It is right inside of the boundary of the mitochondrion (the boundary is the [[outer mitochondrial membrane]]).
|-
| What's on both sides of it || Inside: [[inner mitochondrial membrane]] (separating it from the [[mitochondrial matrix]]), outside: [[outer mitochondrial membrane]] (separating it from the [[cytosol]] or adjacent mitochondria in the [[mitochondrial network]])
|-
| Structural components || The ''intracristal space'' is the part of the intermembrane space between the folds (cristae) of the inner mitochondrial membrane. The ''peripheral space'' is the part of the intermembrane space farther out of the inner mitochondrial membrane.
|-
| pH || About 7.0 to 7.4. Although still a little alkaline, it is less so than the mitochondrial matrix and less so than the rest of the cell, due to the pumping out of protons from the mitochondrial matrix as part of the [[electron transport chain]].
|}

==Size and shape==

===Limitations of study===

Unlike the [[mitochondrion]] as a whole, the intermembrane space of mitochondrion is too small to be seen with a light microscope. The electron microscope that is necessary to see it can be destructive to the living cell and may change the shape of the mitochondrion.

===Shape===

The entire mitochondrion (bounded by the [[outer mitochondrial membrane]]) can be approximated as a rounded cylinder (cylinder with rounded edges) and the mitochondrial matrix (bounded by the [[inner mitochondrial membrane]]) can be approximated as a rounded cylinder that is fully inside it. The intermembrane space is the region that's in the bigger rounded cylinder and outside the smaller rounded cylinder, and its thickness (up to 20 nm) represents the margin around the smaller cylinder.

This crude description captures the concept of the peripheral intermembrane space. The intracristal space is a bunch of little crevices in the inner cylinder.

===Size and volume calculation===

We use this size range for the mitochondrion:

* The length is generally at least 1 <math>\mu m</math> and at most 4 <math>\mu m</math>.
* The tubular radius is generally at least 0.5 <math>\mu m</math> and at most 1 <math>\mu m</math>.

We also use that the thickness of the intermembrane space is about 20 <math>nm</math>.

Illustratively, and using the biggest size estimates, let's say the mitochondrion has a length of 4 <math>\mu m</math>, a tubular radius of 1 <math>\mu m</math>, and an intermembrane space that is uniformly 20 <math>nm</math> thickness. Let's model the mitochondrion and mitochondrial matrix as cylinders.

* Volume of the mitochondrion is <math>\pi r^2 h</math> where <math>r = 1 \mu m, h = 4 \mu m</math>, giving <math>12.57 \mu m^3</math>
* Volume of the mitochondrial matrix (the inner cylinder) is <math>\pi r^2 h</math> where <math>r = 0.98 \mu m, h =3.96 \mu m</math> (these values are obtained by subtracting the thickness of the IMS from the radius and twice the thickness of the IMS from the height), giving <math>11.95 \mu m^3</math>. The difference is <math>0.62 \mu m^3</math>.

A cubic micrometer (<math>\mu m^3</math>) is the same as a femtoliter, or <math>10^{-15}</math> liters. So the volume of the intermembrane space works out to be <math>0.62 fL</math>. But this is the upper end. The lower end would be roughly about 1/16 of this, or about <math>0.04 fL</math>.

Note that this calculation is most faithful for the peripheral IMS. The intercristal IMS is not covered here, but likely does not cover much volume (its significance is more in terms of the high surface area that it covers, not the volume).

===Mass===

Since [[most cellular matter is approximately as dense as water]], we can approximate the density of the intermembrane space using the density of water, which is about 1 gram per milliliter. Based on the volume estimate above, we get that the mass of a mitochondrion is approximately between 0.04 and 0.62 picograms, where a picogram is <math>10^{-12}</math> grams.

==Chemical composition==

===Number of hydrogen ions===

NOTE: In practice, hydrogen ions are rarely floating freely -- they are usually bound to at least one water molecule, forming a hydronium ion. For ease of discourse, we say "hydrogen ion"; the term "proton" may also be used, but it's important to keep in mind that this is referring to single-proton atomic nuclei, not to protons that exist in larger atomic nuclei.

The pH of the IMS ranges between 7.0 and 7.4. In other words, it's a little more alkaline than neutral pH (at human body temperature, neutral pH is about 6.8). Combining this with the size calculation, we can estimate the number of protons (hydrogen ions) in the IMS.

At the upper end would be the case of a pH of 7.0. That means that there are <math>10^{-7}</math> moles of hydrogen per liter. Our upper estimate for IMS volume is <math>0.62 fL = 0.62 * 10^{-15} L</math>, which gives a total of <math>0.62 * 10^{-22}</math> moles of hydrogen ions in the IMS. 1 mole of something is <math>6.023 * 10^{23}</math> many of that, so plugging that in, we get:

<math>0.62 * 10^{-22} * 6.023 * 10^{23} = 37.34</math>

So we get a grand total of 37.34 hydrogen ions in the IMS! That's not a lot of hydrogen ions. Obviously, the numbers here are all approximations -- the actual number of ions at any given time should be an integer. But note that this is using the high-end estimates, so at the lower end of the range, we have even fewer hydrogen ions. Overall, we expect a single-digit or double-digit number of hydrogen ions in the IMS.

The IMS has the ability to freely exchange hydrogen ions across the [[outer mitochondrial membrane]] with both its neighbor mitochondria (the adjacent nodes to it in the [[mitochondrial network]]) and the cytosol. Thus, even though the number of hydrogen ions in a single IMS may seem too small to be stable, the ability to exchange hydrogen ions means there is a bit more stability in numbers. Relatedly, it's worth noting that the cytosolic pH is at the high end (about 7.4). Therefore, protons would be expected to diffuse out from the IMS into the much bigger cytosol, eventually causing the IMS to get to a pH of 4. The reason this doesn't usually happen, and the IMS is able to maintain a slightly lower pH (higher concentration of hydrogen ions) than the surrounding cytosol is the pumping of protons from the mitochondrial matrix across the inner mitochondrial membrane.

===Other small molecules===

As the outer mitochondrial membrane is freely permeable to small molecules, the intermembrane space can be thought of as being contiguous with the cytosol as far as small molecules are concerned. In particular, the concentration of each molecule in the IMS is expected to roughly match the concentration in the cytosol. Hydrogen ions, as discussed in the preceding section, are a partial exception, insofar as the IMS has somewhat higher concentration of hydrogen ions due to receiving these ions regularly from the mitochondrial matrix.

The IMS can differ quite a bit from the mitochondrial matrix, since the inner mitochondrial membrane, that separates the two, is extremely selective.

===Proteins===

Large molecules, such as proteins, cannot freely move through the outer mitochondrial membrane. So, the protein composition of the IMS can (and does) differ from that of the cytosol. It also differs from the protein composition of the mitochondrial matrix, as proteins are not freely transported across the inner mitochondrial membrane.

The intermembrane space cannot ''make'' its own protein, so the protein it does get it must get from the cytosol, and it can get only those proteins from the cytosol that the outer mitochondrial membrane allows.

Intermembrane space of mitochondrion

2024-10-28T05:09:19Z

Vipul: /* Size and shape */

Intermembrane space of mitochondrion

2024-10-28T05:05:32Z

Vipul: /* Summary */

Intermembrane space of mitochondrion

2024-10-28T05:04:45Z

Vipul: /* Definition */

Intermembrane space of mitochondrion

2024-10-28T03:48:19Z

Vipul: /* Size and shape */

{{component of organelle|mitochondrion}}

==Definition==

The '''intermembrane space of mitochondrion''' is a space between the two membranes of a [[mitochondrion]]: the [[outer mitochondrial membrane]] and [[inner mitochondrial membrane]].

==Summary==

{| class="sortable" border="1"
! Item !! Value
|-
| Type of organisms whose cells contain the intermembrane space || Same as the organisms whose cells contain mitochondria: [[eukaryotic cell]]s ''only'', including [[plant cell]]s, [[animal cell]]s, and the cells of [[protist]]s and [[fungus|fungi]]
|-
| Type of cells within the organisms that contain the intermembrane space || Same as the cells that contain mitochondria: all cells except [[red blood cell]]s in [[mammal]]s (other vertebrates ''do'' have mitochondria in their red blood cells).
|-
| Number of intermembrane spaces per cell || Same as the number of mitochondria: 1 to 1000s, depending on the energy needs of the cell
|-
| Size || <math>~200</math> angstrom or <math>~20 nm</math> thickness (very approximate), accounting for less than 5% of the length (less than 10% even if you consider that it's on both sides).
|-
| Location within the mitochondrion || It is right inside of the boundary of the mitochondrion (the boundary is the [[outer mitochondrial membrane]]).
|-
| What's on both sides of it || Inside: [[inner mitochondrial membrane]], outside: [[outer mitochondrial membrane]]
|-
| Structural components || The ''intracristal space'' is the part of the intermembrane space between the folds (cristae) of the inner mitochondrial membrane. The ''peripheral space'' is the part of the intermembrane space farther out of the inner mitochondrial membrane.
|-
| pH || About 7.0 to 7.4. Although still a little alkaline, it is less so than the mitochondrial matrix and less so than the rest of the cell, due to the pumping out of protons from the mitochondrial matrix as part of the [[electron transport chain]].
|}

==Size and shape==

===Limitations of study===

Unlike the [[mitochondrion]] as a whole, the intermembrane space of mitochondrion is too small to be seen with a light microscope. The electron microscope that is necessary to see it can be destructive to the living cell and may change the shape of the mitochondrion.

===Size and volume calculation===

We use this size range for the mitochondrion:

* The length is generally at least 1 <math>\mu m</math> and at most 4 <math>\mu m</math>.
* The tubular radius is generally at least 0.5 <math>\mu m</math> and at most 1 <math>\mu m</math>.

We also use that the thickness of the intermembrane space is about 20 <math>nm</math>.

Illustratively, and using the biggest size estimates, let's say the mitochondrion has a length of 4 <math>\mu m</math>, a tubular radius of 1 <math>\mu m</math>, and an intermembrane space that is uniformly 20 <math>nm</math> thickness. Let's model the mitochondrion and mitochondrial matrix as cylinders.

* Volume of the mitochondrion is <math>\pi r^2 h</math> where <math>r = 1 \mu m, h = 4 \mu m</math>, giving <math>12.57 \mu m^3</math>
* Volume of the mitochondrial matrix (the inner cylinder) is <math>\pi r^2 h</math> where <math>r = 0.98 \mu m, h =3.96 \mu m</math> (these values are obtained by subtracting the thickness of the IMS from the radius and twice the thickness of the IMS from the height), giving <math>11.95 \mu m^3</math>. The difference is <math>0.62 \mu m^3</math>.

A cubic micrometer (<math>\mu m^3</math>) is the same as a femtoliter, or <math>10^{-15}</math> liters. So the volume of the intermembrane space works out to be <math>0.62 fL</math>. But this is the upper end. The lower end would be roughly about 1/16 of this, or about <math>0.04 fL</math>.

Note that this calculation is most faithful for the peripheral IMS. The intercristal IMS is not covered here, but likely does not cover much volume (its significance is more in terms of the high surface area that it covers, not the volume).

===Mass===

Since [[most cellular matter is approximately as dense as water]], we can approximate the density of the intermembrane space using the density of water, which is about 1 gram per milliliter. Based on the volume estimate above, we get that the mass of a mitochondrion is approximately between 0.04 and 0.62 picograms, where a picogram is <math>10^{-12}</math> grams.

==Chemical composition==

===Number of hydrogen ions===

NOTE: In practice, hydrogen ions are rarely floating freely -- they are usually bound to at least one water molecule, forming a hydronium ion. For ease of discourse, we say "hydrogen ion"; the term "proton" may also be used, but it's important to keep in mind that this is referring to single-proton atomic nuclei, not to protons that exist in larger atomic nuclei.

The pH of the IMS ranges between 7.0 and 7.4. In other words, it's a little more alkaline than neutral pH (at human body temperature, neutral pH is about 6.8). Combining this with the size calculation, we can estimate the number of protons (hydrogen ions) in the IMS.

At the upper end would be the case of a pH of 7.0. That means that there are <math>10^{-7}</math> moles of hydrogen per liter. Our upper estimate for IMS volume is <math>0.62 fL = 0.62 * 10^{-15} L</math>, which gives a total of <math>0.62 * 10^{-22}</math> moles of hydrogen ions in the IMS. 1 mole of something is <math>6.023 * 10^{23}</math> many of that, so plugging that in, we get:

<math>0.62 * 10^{-22} * 6.023 * 10^{23} = 37.34</math>

So we get a grand total of 37.34 hydrogen ions in the IMS! That's not a lot of hydrogen ions. Obviously, the numbers here are all approximations -- the actual number of ions at any given time should be an integer. But note that this is using the high-end estimates, so at the lower end of the range, we have even fewer hydrogen ions. Overall, we expect a single-digit or double-digit number of hydrogen ions in the IMS.

The IMS has the ability to freely exchange hydrogen ions across the [[outer mitochondrial membrane]] with both its neighbor mitochondria (the adjacent nodes to it in the [[mitochondrial network]]) and the cytosol. Thus, even though the number of hydrogen ions in a single IMS may seem too small to be stable, the ability to exchange hydrogen ions means there is a bit more stability in numbers. Relatedly, it's worth noting that the cytosolic pH is at the high end (about 7.4). Therefore, protons would be expected to diffuse out from the IMS into the much bigger cytosol, eventually causing the IMS to get to a pH of 4. The reason this doesn't usually happen, and the IMS is able to maintain a slightly lower pH (higher concentration of hydrogen ions) than the surrounding cytosol is the pumping of protons from the mitochondrial matrix across the inner mitochondrial membrane.

2024-08-07T22:52:24Z

Vipul:

Cellbio:429 Too Many Requests error

2024-08-07T22:51:42Z

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This content is copied from [[Ref:Ref:429 Too Many Requests error]].

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You're probably seeing this error because a large number of requests have been made from your IP address over a short period of time. That's probably a lot of requests from you or others who share your IP address (such as your home wi-fi network). Waiting a minute and then retrying should generally work.

If you are an actual human being with a legitimate reason to be browsing the site heavily, first, thank you and sorry about this! We set rate limits to prevent bots, spiders, spammers, and malicious actors from consuming too much of our server's resources so that our server's resources can be devoted to real humans like you. Consider writing to vipulnaik1@gmail.com with your IP address to have the IP address whitelisted. You can get your IP address by [https://www.google.com/search?q=my+ip+address Googling "my IP address"] (scroll down a little bit to where Google includes the IP address in a box). NOTE: If you have both an IPv4 address and an IPv6 address, you should send both; the server supports both IPv4 and IPv6, so either may end up getting used. To check if you have an IPv6 address, try visiting [https://ipv6.google.com/ ipv6.google.com].

If your IP address changes, or you are away from your home network, then you'll get rate-limited again. So if you find yourself getting rate-limited after already having been whitelisted, check if you are on a different IP address than the one for which you requested whitelisting.

File:Site search autocompletion working.png

2024-08-07T22:50:33Z

Vipul:

File:Site search autocompletion broken.png

2024-08-07T22:49:37Z

Vipul:

Cellbio:Enabling site search autocompletion

2024-08-07T22:48:10Z

Vipul: Created page with "Content copied from Ref:Ref:Enabling site search autocompletion. Images used are specific to this site (Cellbio). Site search autocompletion is currently broken by default on this site. This page includes details on how to get it to work, and what's going on. ==What's wrong with site search autocompletion and how to fix it== ===What's wrong=== When you start typing something in the site search bar, you'll see it stuck at "Loading search suggestions" as shown in t..."

Content copied from [[Ref:Ref:Enabling site search autocompletion]]. Images used are specific to this site (Cellbio).

Site search autocompletion is currently broken by default on this site. This page includes details on how to get it to work, and what's going on.

==What's wrong with site search autocompletion and how to fix it==

===What's wrong===

When you start typing something in the site search bar, you'll see it stuck at "Loading search suggestions" as shown in the screenshot below:

[[File:Site search autocompletion broken.png]]

Note that the actual search is still working -- you just have to hit Enter after typing the search query and it'll go to the search results page. It's the autocompletion before you hit Enter that is broken.

===How to fix it===

To fix it, you need to follow these steps:

* Write to vipulnaik1@gmail.com asking for a login to the site. Please include the following with your request: preferred username, preferred initial password (you can change it after logging in), real name (if you want it entered), email address to use (if you want an actual email address by which you can be contacted), and whether you want edit access as well. You don't need edit access for enabling site search autocompletion.
* Log in to the site. Then go to [[Special:Preferences]]. Go to the Appearance section and switch the Skin from "Vector (2022)" to "Vector legacy (2010)".
* Make sure to hit "Save" at the bottom.
* Now you can reload the page or load a new page.

Site search autocompletion should now work. Here's an example:

[[File:Site search autocompletion working.png]]

==More background==

We've recently upgraded the MediaWiki version of this wiki from 1.35.13 to 1.41.2 (see [[Special:Version]]). The upgrade allows us to migrate the wiki to a more modern operating system version running PHP 8. With the current setup for MediaWiki 1.41.2, we're in this situation:

* The "Vector legacy (2010)" skin has site search autocompletion working, but it doesn't render well on small screens. Specifically, even on small mobile screens, it still shows the left menu, and doesn't properly use the MobileFrontend extension settings.
* The "Vector (2022)" skin doesn't have site search autocompletion working (see screenshots in preceding section) but it does render fine on mobile devices.

It is possible to set only one default skin (that is applicable to all non-logged-in users and is the default for logged-in users who have not configured a skin for themselves). So, the selection of default skin comes down to whether it's more important for casual users to have the mobile experience working or to have site search autocompletion working. Based on a general understanding of user behavior, we believe that having a usable mobile experience is more important for casual users than having site search autocompletion.

However, for power users who are using the site extensively, site search autocompletion may be important. That's why we've written this page giving guidance on how to set up site search autocompletion.

2024-04-18T05:10:10Z

Vipul: /* Size and shape */

{{organelle}}

{{TOCright}}

==Definition==

'''Mitochondrion''' (plural '''mitochondria''', also historically called '''bioblast''') is an [[organelle]] found in [[eukaryotic cell]]s whose primary function is to carry out [[aerobic respiration]], i.e., convert energy from a relatively more hard-to-use form (pyruvates) to energy stored in the form of ATP.

==Summary==

{| class="sortable" border="1"
! Item !! Value
|-
| Type of organisms whose cells contain mitochondria || [[Eukaryotic cell]]s ''only'', including [[plant cell]]s, [[animal cell]]s, and the cells of [[protist]]s and [[fungus|fungi]]; some of the more primitive eukaryotic cells (only in unicellular organisms) lack mitochondria; some of them have other similar (and likely evolutionary related) structures such as [[mitosome]]s or [[hydrogenosome]]s. For more, see [[most eukaryotic organisms have mitochondria in most of their cells]].
|-
| Type of cells within the organisms that contain mitochondria || All cells except [[red blood cell]]s in [[mammal]]s (other vertebrates ''do'' have mitochondria in their red blood cells). For more, see [[most eukaryotic organisms have mitochondria in most of their cells]].
|-
| Number of mitochondria per cell || 1 to 1000s, depending on the energy needs of the cell
|-
| Shape || Most mitochondria are tubular (cylindrical, with rounded ends). The tubular radius is usually significantly less than half the diameter, e.g., about 1/4 in one example.<ref name=tubular-radius>{{cite web|url = https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2711342/|title = Diffusion Restrictions Surrounding Mitochondria: A Mathematical Model of Heart Muscle Fibers}}</ref> Some mitochondria are spherical (globular); the transition to spherical/globular shape generally happens due to unusual circumstances such as the loss of membrane potential.<ref name=spherical-contraction>{{cite web|url = https://www.nature.com/articles/s41598-017-18582-6|title = Uncoupled mitochondria quickly shorten along their long axis to form indented spheroids, instead of rings, in a fission-independent manner}}</ref>
|-
| Size || <math>0.5 - 3 \mu m</math> diameter per mitochondrion. In some cells with significant energy needs (such as human heart cells), they could together take up to 1/4 of the cell volume.
|-
| Interconnection || Mitochondria are usually networked with each other, forming a [[mitochondrial network]]. The extent to which the mitochondria are fused with each other depends on the relative rates of fission and fusion. The study of the shape of mitochondrial networks is called [[mitochondrial morphology]] and the study of the change in these over time is called [[mitochondrial dynamics]].<ref>{{cite web|url = https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4672710/|title = What is the function of mitochondrial networks? A theoretical assessment of hypotheses and proposal for future research}}</ref><ref>{{cite web|url = https://bmcbiol.biomedcentral.com/articles/10.1186/1741-7007-11-71|title = Mitochondrial network morphology: building an integrative, geometrical view}}</ref>
|-
| Location within cell || Could be found anywhere in the cell, depending on the cell's energy needs. For instance, in sperm cells, mitochondria are found in the tail to provide power for propulsion.
|-
| Structural components || [[outer mitochondrial membrane]], [[intermembrane space of mitochondrion]], [[inner mitochondrial membrane]], [[cristae]], [[mitochondrial matrix]]
|-
| Chemical constituents || lots of proteins
|-
| Control of the entry and exit of materials || Membranes (hydrophilic/hydrophobic issues), the [[TIM/TOM complex]]
|-
| Function || [[cellular respiration]], i.e., ATP synthesis Control of [[cell cycle]] [[Cellular differentiation]] [[Cell growth]] [[Cell death]]
|-
| Biogenesis || See [[mitochondrial biogenesis]] for more. Mitochondria divide by [[mitochondrial fission]]. This is a type of [[binary fission]], just like bacteria (this is consistent with the [[endosymbiotic theory of mitochondrial origin]]). The process may be regulated to be coordinated with the [[cell cycle]]. The nature of regulation depends on the organism and cell type. Mitochondria can also fuse together ([[mitochondrial fusion]]); the balance of fission and fusion determines the [[mitochondrial dynamics]], i.e., the evolution of mitochondrial networks.
|-
| Evolutionary origin || [[endosymbiotic theory of mitochondrial origin]] -- the mitochondria are evolutionary descendants of endosymbionts (organisms living in the cell in a mutually beneficial relationship with their host)
|-
| Variation between species || [[Mammal]]s do not have mitochondria in their [[red blood cell]]s. In most species, mitochondria is inherited maternally, but there are some species where it is inherited paternally. The shape and structure of mitochondria, and the code of the mitochondrial genome, vary between species.
|-
| Variation between individuals within a species || Mitochondria have their own DNA which (in most eukaryotic organisms) is inherited from the mother. In addition, some of the behavior of the mitochondria is controlled by nuclear DNA.
|-
| Variation between cells within an organism || The number and location of mitochondria depend on the cell's energy needs.
|-
| Quality control || See [[mitochondrial quality control]] for more.
|}

==Size and shape==

{{size measures backgrounder}}

===Size parameters: length and tubular radius===

Most mitochondria have a tubular shape, i.e., a cylindrical shape with rounded ends. The mitochondrion's shape and size are roughly described using these two parameters:

* The ''length'' or (cylinder) ''height'': This is the length along the mitochondrion's tubular axis. When modeling the mitochondrion as a cylinder, this is the height of the cylinder.
* The ''tubular radius'': This is the radius of the tubular cross-section, which looks like a circular disk. When modeling the mitochondrion as a cylinder, this is the radius of the cylinder.

Note that the term ''diameter'' is ambiguous as it could either refer to the length of the mitochondrion (as it is the diameter in the sense of being the maximum possible length within the mitochondrion) or to the diameter of the tubular cross-section (i.e., twice the tubular radius). It is therefore better to use the terms "length" and "tubular radius" that are more unambiguous. If using diameter to refer to the tubular diameter, it is better to say "tubular diameter" to make it clear.

===Qualia of shape: spherical / globular shape versus the more typical tubular shape===

The shape of the mitochondrion can be roughly gauged by taking the ratio of the length to the tubular radius; this ratio should not be much less than 2.

* A ratio of around 2 indicates that the mitochondrion is close to spherical. Such mitochondria are called spherical or globular mitochondria.
* A ratio greater than 2 indicates a more typical tubular (elongated) mitochondrion shape. A typical ratio is around 4; for instance, that's the ratio seen in cardiac cells in one study.<ref name=tubular-radius/>

The shape of a mitochondrion has significance for its functionality. The tubular shape is tied to maintaining membrane potential, which is a key aspect of mitochondrial function, and a spherical/globular shape is often seen as a result of a loss of membrane potential.<ref name=spherical-contraction/>

===Value ranges for size parameters===

* The length is generally at least 1 <math>\mu m</math> and at most 4 <math>\mu m</math>.
* The tubular radius is generally at least 0.5 <math>\mu m</math> and at most 1 <math>\mu m</math>.

===Cross-sectional surface area===

Cross-sectional surface area along the tubular cross-section is important because cross-sections are the things we put under the microscope. The cross-section is approximately a circular disk whose radius is the tubular radius.

The formula for cross-sectional surface area is <math>\pi r^2</math> where <math>\pi</math> is the constant [[wikipedia:pi|pi]] (about 3.14159) and <math>r</math> is the tubular radius.

Using the above value ranges, we have:

* Low-end estimate using <math>r = 0.5 \mu m</math>: <math>0.785 \mu m^2</math>
* High-end estimate using <math>r = 1 \mu m</math>: <math>3.142 \mu m^2</math>

Rounding, we often say that the cross-sectional surface area of mitochondria is in the range of 0.75 to 3 <math>\mu m^2</math>.

===Total surface area===

The surface area of mitochondria (area of the [[outer mitochondrial membrane]]) can be modeled by approximating it as a capped cylinder where the radius <math>r</math> is the radius of the tubular cross-section and the height <math>h</math> is the length (i.e., the length along its tubular axis).

The formula for surface area of a capped cylinder is <math>2\pi r(r + h)</math>.

Using the value ranges above, we have:

* Low-end estimate using <math>r = 0.5, h = 1</math>: <math>4.7 \mu m^2</math>
* High-end estimate using <math>r = 1, h = 4</math>: <math>31 \mu m^2</math>

Rounding, we can say that the surface area of mitochondria is about 5 to 30 <math>\mu m^2</math>.

===Volume===

We can estimate the volume of the mitochondrion as a cylinder with radius equal to the tubular radius and height equal to the length.

The formula for the volume is <math>\pi r^2 h</math> where <math>r</math> is the radius (tubular radius) and <math>h</math> is the height (length).

We therefore obtain these estimates:

* Low-end estimate using <math>r = 0.5, h = 1</math>: <math>0.785 \mu m^3</math>
* High-end estimate using <math>r = 1, h = 4</math>: <math>12.57 \mu m^3</math>

A cubic micrometer (<math>\mu m^3</math>) is the same as a femtoliter, or <math>10^{-15}</math> liters.

===Mass===

Since [[most cellular matter is approximately as dense as water]], we can approximate the density of mitochondria using the density of water, which is about 1 gram per milliliter. Based on the volume estimate above, we get that the mass of a mitochondrion is approximately between 0.785 and 12.57 picograms, where a picogram is <math>10^{-12}</math> grams.

===Comparison with cell sizes===

''Comparison with prokaryotic cells'': The mitochondrion size is roughly the lower end of the size range for [[prokaryotic cell]]s (which is explained by their evolutionary origin; see [[endosymbiotic theory of mitochondrial origin]]).

''Comparison with eukaryotic cells'': Mitochondria are found in [[eukaryotic cell]]s (''not'' prokaryotic cells) which have a diameter in the <math>10-100 \mu m</math> range. Thus, the dimensions of an individual mitochondrion are about 1/100 to 1/10 the diameter of the whole cell and hence about 1/10^6 to 1/10^3 the ''volume'' of the whole cell.

The total volume of the mitochondria depends on the number of mitochondria as well. It could be as large as 1/5 (or 20%) of cell volume.

===Comparison with wavelengths of light and implications for visibility under microscopes===

The wavelength of visible light is in the range <math>0.4-0.7 \mu m</math>, which is approximately equal to the tubular radius and a little less than the length of the mitochondrion. Thus, mitochondria can be viewed with [[light microscope]]s (whose resolution is limited to <math>0.2 \mu m</math>) but their internal structures cannot be clearly identified. [[Electron microscope]]s (that cannot be used on live cells) need to be used to study the structure of mitochondria well.

===Comparison with other organelles===

Mitochondria are among the bigger of the cellular organelles. The mitochondrion, nucleus, and Golgi bodies are the cellular organelles big enough to be identified using a light microscope, and for that reason are among the oldest organelles to be identified and studied (even prior to the advent of electron microscopes).

===Comparison with molecules===

A water molecule's size is about <math>2.75 * 10^{-10} m</math>, which is a little under 1/1000 of the low end for the tubular radius of a mitochondrion (0.5 <math>\mu m</math>). Since this is in just one dimension (length) we need to square when thinking about cross-sectional area and cube when thinking about volume. Roughly speaking, a cross section has space for millions of water molecules, and the mitochondrion has space for billions of water molecules.

==Physical structure==

The mitochondrion has the following structural components:

{| class="sortable" border="1"
! Component !! Thickness !! Thickness as percentage of mitochondrial diameter (approx.). -- double this value to account for it being on both sides)
|-
| [[outer mitochondrial membrane]] || 60 - 75 angstrom (6 to 7.5 nm)|| 0.2-1%
|-
| [[intermembrane space of mitochondrion]] || ~200 angstrom (20 nm) || 1-4%
|-
| [[inner mitochondrial membrane]] || 70 angstrom (7 nm) || 0.2-1%
|-
| [[cristae]] || ||
|-
| [[mitochondrial matrix]] || ||
|}

==Interconnection, propagation, and dynamics==

===Mitochondrial networks, fission and fusion===

In most cells, the mitochondria are interconnected as a network called the [[mitochondrial network]]. The mitochondria in the network align along their tubular axis. The network could be a single curve (without branching) or it could have branches, depending on details specific to the cell.

Mitochondria are constantly undergoing [[mitochondrial fission]] (one mitochondrion splitting into two, that then go on to form adjacent nodes in the mitochondrial network) and [[mitochondrial fusion]] (two adjacent mitochondria in the mitochondrial network fusing into one).

The relative rates of fission and fusion determine how the mitochondrial network evolves over time.

==Laboratory analysis==

===Forms in which mitochondria are studied in the lab===

* Mitochondria may be studied in situ, in vivo in living cells.
* Mitochondria can be studied as [[isolated mitochondrion|isolated mitochondria]], removed from the cell but with their outer mitochondrial membrane still intact.
* Mitochondria can be studied as [[mitoplast]]s, which are like isolated mitochondria but with the outer mitochondrial membrane removed.

===Analysis of mitochondria in living cells using a light microscope (in situ, in vivo)===

The size of a mitochondrion (<math>0.5 - 3 \mu m</math>) is slightly higher than the best possible resolution of [[light microscope]]s (about <math>0.2 \mu m</math>). The internal structures of mitochondria are too small to be visible under light microscopes (for instance, the intermembrane space is 20 nm in thickness, which is 1/10 of the resolution that light microscopes afford).

In order to make the mitochondria stand out clearly under the light microscope, a potential-sensitive dye such as J1c, TMRE, or TMRM is used. The dye picks up on the electrochemical potential gradient across the inner mitochondrial membrane and so each mitochondrion shows up as a dot with the color of the dye (under the light microscope).

The light microscope and dye can be used for mitochondria in live cells, and in particular can be used to look at [[mitochondrial network]]s and [[mitochondrial dynamics]] (the change to mitochondrial networks over time).

===Analysis of internal structure of mitochondria (outside living cells) using an electron microscope===

An [[electron microscope]] is needed to achieve the resolution necessary to study the internal structures of the mitochondrion. Electron microscopes tend to destroy living cells, so they cannot be used to study the dynamics of mitochondria in living cells.

==References==