Structure and Function of Mitochondria and Cell Membrane

Mitochondria :-

Mitochondria

 (sing.: mitochondrion), unless specifically stained, are not easily visible under the microscope.

The number of mitochondria per cell  is variable depending on the physiological activity of the cells.

 In terms of shape and size also, considerable degree of variability is observed.

Typically it is sausage-shaped or cylindrical having a diameter of 0.2-1.0μm (average 0.5μm) and length 1.0-4.1μm.

 Each mitochondrion is a double membrane-bound structure with the outer membrane and the innermembrane dividing its lumen distinctly into two aqueous compartments, i.e., the outer compartment and the inner compartment.

The inner compartment is called the matrix.

The outer membrane forms the continuous limiting boundary of the organelle.

 The inner membrane forms a number of infoldings called the cristae (sing.: crista) towards the matrix .

The cristae increase the surface area. The two membranes have their own specific enzymes associated with the mitochondrial function.

 Mitochondria are the sites of aerobic respiration. They produce cellular energy in the form of ATP, hence they are called ‘power houses’ of the cell.

The matrix also possesses single circular DNA molecule, a few RNA molecules, ribosomes (70S) and the components required for the synthesis of proteins.

The mitochondria divide by fission.

 Cell Membrane :-

Cell Membrane

The detailed structure of the membrane was studied only after the advent of the electron microscope in the 1950s. Meanwhile, chemical studies on the cell membrane, especially in human red blood cells (RBCs), enabled the scientists to deduce the possible structure of plasma membrane.

 These studies showed that the cell membrane is composed of lipids that are arranged in a bilayer.

 Also, the lipids are arranged within the membrane with the polar head towards the outer sides and the hydrophobic tails towards the inner part.

This ensures that the nonpolar tail of saturated hydrocarbons is protected from the aqueous environment .

The lipid component of the membrane mainly consists of phosphoglycerides. Later, biochemical investigation clearly revealed that the cell membranes also possess protein and carbohydrate.

The ratio of protein and lipid varies considerably in different cell types.

 In human beings, the membrane of then erythrocyte has approximately 52 per cent protein and 40 per cent lipids.

 Depending on the ease of extraction, membrane proteins can be classified as integral or peripheral. Peripheral proteins lie on the surface of membrane while the integral proteins are partially or totally buried in the membrane.

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