These are the largest particulate components of the cytoplasm and represent upto 15% -20% of the dry weight of the cell. They vary in shape (spherical, filamentous, sausage shaped) and size (0.5 to 3μ long 0.1 to 0.6μ wide).The number varies with the size and energy requirements of the cell. For eg. flight muscles in birds contain rich amount of mitochondria when compared to any other parts of the body
Electron microscopic studies show that a mitochondrion has two membranes inner and outer which are separated from each other by 50 to 100oA. The outer and inner membranes differ in lipid composition and in enzyme content.
The inner membrane is very much folded to form shelf - like structures of varying width. These shelf - like structures, known as internal ridgs or cristae, extent into matrix of the mitochondrion structure. Thus two structurally different space can be distinguished, the intracristae space and the matrix space (Fig. 1.5). The matrix space is rich in enzymes. The inner membrane shows the existance of knob like structures, which are proteins involved in biological oxidations.
Functions : The mitochondria are the ‘power houses’ of the cell, where carbohydrates, lipids and amino acids are oxidised to CO2 and H2O by molecular oxygen, and the energy set free is stored in the form of adenosine triphosphate (ATP). The enzymes involved in this energy conversion are located in the inner membrane.