Mitochondria

Mitochondria is the plural of mitochondrion. The mitochondrion is a cell organelle whose main function is to produce ATP (adenosine triphosphate) from pyruvate, ketone bodies, and fatty acid. ATP is necessary for protein synthesis, muscle contraction, and ciliary beating. The body cells may contain few or many mitochondria. Liver cells usually have between 500 and 1000 of them. Nerve cells even more. Having the characteristics of an autonomous organism, they move within the cell as they undergo changes in shape.

Just as a power plant generates AC electricity from different fuels, such as gas or coal, this cell organelle produces the chemical energy in the form of ATP. The different types of fuels it utilizes to produce it are pyruvate (end product from the degradation of glucose), ketone bodies, and fatty acids.

Structure

The mitochondria are about the size of a small bacterium, measuring between 0.5 to 1 micron in width, and 2 to 4 microns in length. They consist of two membranes, with one surrounding the other. Inside them, there is an amorphous matrix, which contains enzymes. The outer membrane is the outer boundary of the mitochondrion,while the inner membrane has a series of folds which are called cristae. These folds stick out into the internal compartment of this organelle. Both the outer and the inner membrane are composed of a phospholipid protein bilayer.

In order to be able to produce ATP, the mitochondrion needs chemical catalysts. These are enzymes, such as pyruvate dehydrogenase, citrate synthetase, and NADH-cytochrome C oxidoreductase. The mitochondria are often found in cells which requires substantial amount of ATP. In striated muscle tissue, mitochondria are located between myofribils and they supply ATP necessary for muscle contraction. They are also found near the endoplasmatic reticulum as they supply ATP for protein synthesis. The mitochondrion contains its own DNA, which is different from the cell nucleus DNA.

Below, electromicrograph of mitochondria contained in a cell. OM=outer membrane, and IM=inner membrane.