Mitochondria | External and Internal Structure | and Function Mitochondria

Mitochondria 

Mitochondria (singular: mitochondrion) are present in all eukaryotic cells. Some cells have a single large mitochondrion, but more often a cell has hundreds or even thousands of mitochondria; the number correlates with the cell's level of metabolic activity. For example, cells that move or contract have proportionally more mitochondria per volume than less active cells. Mitochondria are capable to divide themselves (self-replicating) in order to increase their number. They divide by fission.

External Structure of  Mitochondria :

Mitochondria are cylindrical or rod shaped structures. They are enclosed by double membrane, the outer membrane and the inner membrane. The outer membrane is smooth and somewhat like a sieve due to presence of porins. These are special proteins responsible for the transport of molecules across the membrane. Porins allow free passage of various molecules into the Inter-membrane space. 

Internal Structure of  Mitochondria :

The inner membrane is selectively permeable and folded inwards. The folds are called cristae which serve to increase the surface area. The inner surface of cristae has granular structures called F0-F1 particles. These particles are actually ATP synthase (see section 4.2.7) enzymes. In addition, several other complexes are also found in inner mitochondrial membrane, which serve as electron carriers in electron transport chain. The inner membrane divides the mitochondrion into two internal compartments. The first is the intermembrane space, the narrow region between the inner and outer membranes. The second compartment, the mitochondrial matrix, is enclosed by the inner membrane. Mitochondrial matrix is a jelly like material that contains a small circular DNA, all kinds of RNA, ribosomes (70S) and enzymes. The presence of these components indicates that mitochondria have their own genetic system. It means, the protein, which are required by mitochondria are synthesized by their own metabolic machinery.

Diagram Mitochondria Structure

Function of Mitochondria :

Mitochondria are the sites of cellular respiration, the metabolic process that uses oxygen to generate ATP by extracting energy from sugars, fats, and other organic compounds. Enzymes in the matrix catalyze some of the steps of cellular respiration like Krebs cycle. Other proteins that function in ATP generation through electron transport chain are found into the inner membrane.

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