Lipid bilayer - Revision history

Vipul: /* Two-tailed phosopholipids */

2024-12-15T08:40:56Z

Two-tailed phosopholipids

← Older revision		Revision as of 08:40, 15 December 2024
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	==Confusion with other twos==		==Confusion with other twos==

	===Two-tailed ~~phosopholipids~~===		===Two-tailed phospholipids===

	A phospholipid is a ''two-tailed'' lipid. Thus, a phospholipid bilayer has two ''two''s in it: one describing the two tails of each molecule, and the other describing the fact that the layer is two molecules thick. The ''bi''layer refers to the latter. Note that whereas the two tails of each molecule are (approximately) parallel to one another, so that their thickness doesn't add up, the thickness of the two layers of the bilayer does add up (because they stack up on top of each other).		A phospholipid is a ''two-tailed'' lipid. Thus, a phospholipid bilayer has two ''two''s in it: one describing the two tails of each molecule, and the other describing the fact that the layer is two molecules thick. The ''bi''layer refers to the latter. Note that whereas the two tails of each molecule are (approximately) parallel to one another, so that their thickness doesn't add up, the thickness of the two layers of the bilayer does add up (because they stack up on top of each other).

Vipul: /* Two-tailed phosopholipids */

2024-12-15T08:40:46Z

Two-tailed phosopholipids

← Older revision		Revision as of 08:40, 15 December 2024
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	===Two-tailed phosopholipids===		===Two-tailed phosopholipids===

	A phospholipid is a ''two-tailed'' lipid. Thus, a phospholipid bilayer has two ''two''s in it: one describing the two tails of each molecule, and the other describing the fact that the layer is two molecules thick. The ''bi''layer refers to the latter. Note that whereas the two tails of each molecule are (approximately) parallel to one another, so that their thickness doesn't add up, the thickness of the two layers of the bilayer does add up (because they stack up on top of each other.		A phospholipid is a ''two-tailed'' lipid. Thus, a phospholipid bilayer has two ''two''s in it: one describing the two tails of each molecule, and the other describing the fact that the layer is two molecules thick. The ''bi''layer refers to the latter. Note that whereas the two tails of each molecule are (approximately) parallel to one another, so that their thickness doesn't add up, the thickness of the two layers of the bilayer does add up (because they stack up on top of each other).

	===Double bilayers===		===Double bilayers===

Vipul: /* Physical structure */

2024-10-28T06:18:46Z

Physical structure

← Older revision		Revision as of 06:18, 28 October 2024
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	Note that the "tail" here refers to ''all'' the hydrophobic tails of the molecule. If the molecule is two-tailed (as is the case with [[phospholipid]]s) the two tails both point in the same direction, toward the outer leaflet.		Note that the "tail" here refers to ''all'' the hydrophobic tails of the molecule. If the molecule is two-tailed (as is the case with [[phospholipid]]s) the two tails both point in the same direction, toward the outer leaflet.

			==Chemical constituents==

			===Hydrophilic head and hydrophilic tails===

			Note that this applies separately to each individual lipid molecule in the lipid bilayer (in either the outer leaflet or the inner leaflet). Different lipid molecules could be of different types, and (with the exception of cholesterol), even within the same type, there could be many different choices of actual molecules depending on the selection of fatty acid(s) and potentially the choice of hydrophilic head.

			Below are some of the possibilities for the head and tails based on the kind of lipid.

			{\| class="sortable" border="1"
			! Type of lipid !! Hydrophilic head !! Type of tail !! Number of tails
			\|-
			\| [[phospholipid]] \|\| phosphate \|\| fatty acid \|\| 2
			\|-
			\| [[sphingolipid]] \|\| sphingoid base of some sort \|\| fatty acid \|\| 1 (at least, 1 usable, maybe 2 in theory?)
			\|-
			\| [[glycolipid]] \|\| sugar residue \|\| fatty acid \|\| 1
			\|-
			\| [[cholesterol]] \|\| hydroxyl group \|\| rest of the cholesterol molecule \|\| 1
			\|}

			===Selection of fatty acid and whether and how saturated it is===

			Each of the fatty acid tails could be chosen as a saturated or unsaturated fatty acid (here, "saturated" means only single C-C bonds; unsaturated means at least one C=C double bond). The unsaturated fatty acid could be chosen as a monounsaturated or polyunsaturated fatty acid. The polyunsaturated fatty acid could be chosen as an <math>\omega</math>-3 or <math>\omega</math>-6 fatty acid.

			In general, greater use of unsaturated fatty acids results in greater flexibility of the biological membrane, and greater use of saturated fatty acids results in greater rigidity of the biological membrane. The mechanism is as follows: the presence of double bounds forces the fatty acid to take up more space, due to local rigidity created by the pi-bond. This means that the fatty acid tails cannot be packed that much, and have a bit more free space, and this is what gives the membrane flexibility. Conversely, with only single bonds, the tails can be packed more tightly. So, it seems that the greater local rigidity imposed by double bonds is what creates overall more flexibility for the membrane.

Vipul: /* Definition */

2024-10-28T06:02:49Z

Definition

← Older revision		Revision as of 06:02, 28 October 2024
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	A '''lipid bilayer''' is a thin membrane (surrounding a cell or organelle) that is two molecules thick, with both molecules being [[lipid]]s with a hydrophilic head and hydrophobic tail. The hydrophilic head of the outer molecule points outward to the (usually aqueous) external environment, and the hydrophilic head of the inner molecule points inward to the cell or organelle being surrounded by the bilayer. The hydrophobic tails both point inward toward each other.		A '''lipid bilayer''' is a thin membrane (surrounding a cell or organelle) that is two molecules thick, with both molecules being [[lipid]]s with a hydrophilic head and hydrophobic tail. The hydrophilic head of the outer molecule points outward to the (usually aqueous) external environment, and the hydrophilic head of the inner molecule points inward to the cell or organelle being surrounded by the bilayer. The hydrophobic tails both point inward toward each other.

	Lipid bilayers constitute [[biological membrane]]s, which, in addition to the lipid bilayer, contain embedded proteins called [[integral membrane protein]]s. Examples of biological membranes are [[cell membrane]]s (in both [[prokaryotic cell]]s and [[eukaryotic cell]]s) as well as the membranes of cellular [[organelle]]s (mostly in [[eukaryotic cell]]s). The most typical examples of lipid bilayers that occur in cell membranes and organelle membranes are those where the lipid is a [[phospholipid]].		Lipid bilayers constitute [[biological membrane]]s, which, in addition to the lipid bilayer, contain embedded proteins called [[integral membrane protein]]s. Examples of biological membranes are [[cell membrane]]s (in both [[prokaryotic cell]]s and [[eukaryotic cell]]s) as well as the membranes of cellular [[organelle]]s (mostly in [[eukaryotic cell]]s). The most typical examples of lipid bilayers that occur in cell membranes and organelle membranes are those where the lipid is a [[phospholipid]]. Other possibilities for the lipid include [[sphingolipid]]s, [[glycolipid]]s, and cholesterol.

	[[File:Lipid_bilayer_section.gif]]		[[File:Lipid_bilayer_section.gif]]

Vipul: /* Summary */

2024-10-28T06:00:35Z

Summary

← Older revision		Revision as of 06:00, 28 October 2024
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	\| Chemical constituents \|\| The lipid molecules, which are usually [[phospholipid]]s in the case of cell membranes and organelle membranes. Note that the lipid making up the outer leaflet may differ from the lipid making up the inner leaflet.		\| Chemical constituents \|\| The lipid molecules, which are usually [[phospholipid]]s in the case of cell membranes and organelle membranes. Note that the lipid making up the outer leaflet may differ from the lipid making up the inner leaflet.
	\|-		\|-
	\| Function \|\| Controls the entry and exit of materials between the cell or organelle and the environment. Specifically, the hydrophobic tails attempt to block water-soluble substances from crossing the lipid bilayer. There are a number of special mechanisms in use (depending on the cell or organelle) that are used to transport materials across the membrane).		\| Function \|\| Controls the entry and exit of materials between the cell or organelle and the environment. Specifically, the hydrophobic tails attempt to block water-soluble substances from crossing the lipid bilayer. There are a number of special mechanisms in use (depending on the cell or organelle) that are used to transport materials across the membrane.
	\|}		\|}

Vipul: /* Double bilayers */

2024-10-28T05:51:44Z

Double bilayers

← Older revision		Revision as of 05:51, 28 October 2024
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	* In the case of the [[nucleus]], the membrane is folded on top of itself		* In the case of the [[nucleus]], the membrane is folded on top of itself
	* In the case of the [[mitochondrion]], there is a distinct [[inner mitochondrial membrane]] and [[outer mitochondrial membrane]])		* In the case of the [[mitochondrion]] and [[chloroplast]], there is a distinct [[inner mitochondrial membrane]] and [[outer mitochondrial membrane]])

	The ''double'' here is distinct from the ''bi''layer double. In the case of a double membrane where each membrane constitutes a bilayer, we expect a <math>2 \times 2 = 4</math>-molecule thick layer.		The ''double'' here is distinct from the ''bi''layer double. In the case of a double membrane where each membrane constitutes a bilayer, we expect a <math>2 \times 2 = 4</math>-molecule thick layer. Note that for organelles with distinct inner and outer membranes, there is an intermembrane space (such as [[intermembrane space of mitochondrion]]) whose thickness is a small multiple (within an order of magnitude) of the thickness of the lipid bilayers.

	==Summary==		==Summary==

Vipul: /* Two-tailed phosopholipids */

2024-10-28T05:50:17Z

Two-tailed phosopholipids

← Older revision		Revision as of 05:50, 28 October 2024
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	===Two-tailed phosopholipids===		===Two-tailed phosopholipids===

	A phospholipid is a ''two-tailed'' lipid. Thus, a phospholipid bilayer has two ''two''s in it: one describing the two tails of each molecule, and the other describing the fact that the layer is two molecules thick. The ''bi''layer refers to the latter.		A phospholipid is a ''two-tailed'' lipid. Thus, a phospholipid bilayer has two ''two''s in it: one describing the two tails of each molecule, and the other describing the fact that the layer is two molecules thick. The ''bi''layer refers to the latter. Note that whereas the two tails of each molecule are (approximately) parallel to one another, so that their thickness doesn't add up, the thickness of the two layers of the bilayer does add up (because they stack up on top of each other.

	===Double bilayers===		===Double bilayers===

Vipul: /* Two-tailed phosopholipids */

2012-05-27T15:33:42Z

Two-tailed phosopholipids

← Older revision		Revision as of 15:33, 27 May 2012
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	===Two-tailed phosopholipids===		===Two-tailed phosopholipids===

	A phospholipid is a ''two-tailed'' lipid. Thus, a phospholipid bilayer has two ''two''s in it: one describing the two tails of each molecule, and the other ~~dscribing~~ the fact that the layer is two molecules thick. The ''bi''layer refers to the latter.		A phospholipid is a ''two-tailed'' lipid. Thus, a phospholipid bilayer has two ''two''s in it: one describing the two tails of each molecule, and the other describing the fact that the layer is two molecules thick. The ''bi''layer refers to the latter.

	===Double bilayers===		===Double bilayers===

Vipul at 15:33, 27 May 2012

2012-05-27T15:33:17Z

← Older revision		Revision as of 15:33, 27 May 2012
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	Lipid bilayers constitute [[biological membrane]]s, which, in addition to the lipid bilayer, contain embedded proteins called [[integral membrane protein]]s. Examples of biological membranes are [[cell membrane]]s (in both [[prokaryotic cell]]s and [[eukaryotic cell]]s) as well as the membranes of cellular [[organelle]]s (mostly in [[eukaryotic cell]]s). The most typical examples of lipid bilayers that occur in cell membranes and organelle membranes are those where the lipid is a [[phospholipid]].		Lipid bilayers constitute [[biological membrane]]s, which, in addition to the lipid bilayer, contain embedded proteins called [[integral membrane protein]]s. Examples of biological membranes are [[cell membrane]]s (in both [[prokaryotic cell]]s and [[eukaryotic cell]]s) as well as the membranes of cellular [[organelle]]s (mostly in [[eukaryotic cell]]s). The most typical examples of lipid bilayers that occur in cell membranes and organelle membranes are those where the lipid is a [[phospholipid]].

	[[~~Commons:~~File:Lipid_bilayer_section.gif]]		[[File:Lipid_bilayer_section.gif]]

	==Confusion with other twos==		==Confusion with other twos==

Vipul at 15:27, 27 May 2012

2012-05-27T15:27:11Z

← Older revision		Revision as of 15:27, 27 May 2012
Line 3:		Line 3:
	A '''lipid bilayer''' is a thin membrane (surrounding a cell or organelle) that is two molecules thick, with both molecules being [[lipid]]s with a hydrophilic head and hydrophobic tail. The hydrophilic head of the outer molecule points outward to the (usually aqueous) external environment, and the hydrophilic head of the inner molecule points inward to the cell or organelle being surrounded by the bilayer. The hydrophobic tails both point inward toward each other.		A '''lipid bilayer''' is a thin membrane (surrounding a cell or organelle) that is two molecules thick, with both molecules being [[lipid]]s with a hydrophilic head and hydrophobic tail. The hydrophilic head of the outer molecule points outward to the (usually aqueous) external environment, and the hydrophilic head of the inner molecule points inward to the cell or organelle being surrounded by the bilayer. The hydrophobic tails both point inward toward each other.

	Lipid bilayers constitute [[biological membrane]]s, which, in addition to the lipid bilayer, contain embedded proteins called [[integral membrane protein]]s. Examples of biological membranes are [[cell membrane]]s (in both [[prokaryotic cell]]s and [[eukaryotic cell]]s) as well as the membranes of cellular [[organelle]]s (mostly in [[eukaryotic cell]]s). The most typical examples of lipid bilayers that occur in cell membranes and organelle membranes are those where the lipid is a [[phospholipid]]~~. A phospholipid is a ''two-tailed'' lipid. Note however that this ''two'' describes two tails of each single molecule and is distinct from the ''two'' that is part of the ''bi''layer definition~~.		Lipid bilayers constitute [[biological membrane]]s, which, in addition to the lipid bilayer, contain embedded proteins called [[integral membrane protein]]s. Examples of biological membranes are [[cell membrane]]s (in both [[prokaryotic cell]]s and [[eukaryotic cell]]s) as well as the membranes of cellular [[organelle]]s (mostly in [[eukaryotic cell]]s). The most typical examples of lipid bilayers that occur in cell membranes and organelle membranes are those where the lipid is a [[phospholipid]].

	~~Also~~, ~~when people talk~~ of double membranes ~~(as in~~ the case of the [[nucleus]], ~~where~~ the membrane is folded ~~onto~~ itself~~, and~~ the [[mitochondrion]], ~~where~~ there is a distinct [[inner mitochondrial membrane]] and [[outer mitochondrial membrane]])~~, this refers to an~~ ''~~additional~~'' ~~doubling over and above~~ the ~~bilayer, so that there are effectively~~ ''~~four~~'' ~~layers~~ of ~~molecules~~.		[[Commons:File:Lipid_bilayer_section.gif]]

			==Confusion with other twos==

			===Two-tailed phosopholipids===

			A phospholipid is a ''two-tailed'' lipid. Thus, a phospholipid bilayer has two ''two''s in it: one describing the two tails of each molecule, and the other dscribing the fact that the layer is two molecules thick. The ''bi''layer refers to the latter.

			===Double bilayers===

			There are some contexts where biological membranes are ''double'' membranes:

			* In the case of the [[nucleus]], the membrane is folded on top of itself
			* In the case of the [[mitochondrion]], there is a distinct [[inner mitochondrial membrane]] and [[outer mitochondrial membrane]])

			The ''double'' here is distinct from the ''bi''layer double. In the case of a double membrane where each membrane constitutes a bilayer, we expect a <math>2 \times 2 = 4</math>-molecule thick layer.

	==Summary==		==Summary==