Mitochondrial matrix

Definition

The mitochondrial matrix is the interior part of the mitochondrion, specifically the part on the inside of the inner mitochondrial membrane. It comprises the bulk of the volume of the mitochondrion. The citric acid cycle occurs inside the mitochondrial matrix.

Summary

Item	Value
Type of organisms whose cells contain the mitochondrial matrix	Same as the type of organisms whose cells contain mitochondria: eukaryotic cells only, including plant cells, animal cells, and the cells of protists and fungi
Type of cells within the organisms that contain the mitochondrial matrix	Same as the cells that contain mitochondria: All cells except red blood cells in mammals (other vertebrates do have mitochondria in their red blood cells).
Number of mitochondrial matrices per cell	One per mitochondrion, so 1 to 1000s, depending on the energy needs of the cell
Size	$0.5-1.0\mu m$ diameter per mitochondrial matrix; this is over 90% of the diameter of the mitochondrion; the mitochondrial matrix is the bulk of the volume of the mitochondrion.
Location within mitochondrion	The mitochondrial matrix is located in the interior of the mitochondrion; it is bounded by the inner mitochondrial membrane that in turn is surrounded by the intermembrane space, that in turn is bounded by the outer mitochondrial membrane.
Structural components	Mitochondrial DNA, ribosomes, soluble enzymes, small organic molecules, nucleotide cofactors, and inorganic ions
pH	About 7.8, compared with pH of 7.0 for water and pH of 7.0 to 7.4 for the intermembrane space. The high pH represents an alkaline environment, and is a result of the pumping out of protons via the electron transport chain.