Mitochondria are organelles that generate energy for cell functioning. They are rod-shaped or sausage-shaped structures that are 0.5–1 micrometers in diameter. Mitochondria have two membranes, an outer membrane and an inner membrane that contains folds called "cristae".  The cristae increase the surface area of the inner membrane, which allows for more locations for ATP production.  Mitochondria also have their own DNA, called mitochondrial DNA (mtDNA). mtDNA is a double-stranded, circular molecule that contains 37 genes. The mtDNA-encoded polypeptides are subunits of enzyme complexes of... Show more

Mitochondria are organelles that generate energy for cell functioning. They are rod-shaped or sausage-shaped structures that are 0.5–1 micrometers in diameter. Mitochondria have two membranes, an outer membrane and an inner membrane that contains folds called "cristae". 
The cristae increase the surface area of the inner membrane, which allows for more locations for ATP production. 
Mitochondria also have their own DNA, called mitochondrial DNA (mtDNA). mtDNA is a double-stranded, circular molecule that contains 37 genes. The mtDNA-encoded polypeptides are subunits of enzyme complexes of the oxidative phosphorylation system.

Mitochondria have many functions, including:
Energy conversion: Mitochondria convert pyruvate and the citric acid cycle, and release heat.
Aerobic respiration: Mitochondria play a key role in the cell's metabolic process, and most aerobic respiration takes place in the mitochondria.
ATP production: Mitochondria produce and store energy in the form of ATP, which is then released as needed.
Calcium ion storage: Mitochondria store and release calcium ions.
Cellular proliferation regulation: Mitochondria regulate cellular proliferation. 

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