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### 8.5.1 Cell Membrane The detailed structure of the membrane was studied only after the advent of the electron microscope in the 1950s. Chemical studies, especially in human red blood cells (RBCs), enabled the scientists to deduce the possible structure of plasma membrane. These studies showed th...

### 8.5.1 Cell Membrane The detailed structure of the membrane was studied only after the advent of the electron microscope in the 1950s. Chemical studies, 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 mainly composed of lipids and proteins. The major lipids are phospholipids that are arranged in a bilayer. 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. In addition to phospholipids, the membrane also contains cholesterol. 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 the 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 and peripheral. Peripheral proteins lie on the surface of the membrane while the integral proteins are partially or totally buried in the membrane. - **Sugar** - **Peripheral Protein** - **Integral Protein** - **Cholesterol** **Figure 8.4 Fluid mosaic model of plasma membrane** - **Phospholipid bilayer**