Cell membrane or plasma membrane is the living outer boundary of cells. It separates cytoplasm from the external environment.
Major chemical constituents of plasma membrane are:
1. Proteins : These are the main components of biological membrane. It constitutes about 60 - 75% by dry weight. Three types of proteins are present in cell membrane.
- Structural proteins : These form the structural framework of membrane.
- Carrier proteins : These are concerned with the active transport across the membrane.
- Enzymes : Include ATPase, Phosphatase, RNAase, Esterase, etc. They mediate active transport and other reactions.
2. Lipids : Lipids constitute about 20-40% of plasma membrane by dry weight. It contains a hydrophilic head and hydrophobic tail. Main lipids in membrane are phospholipids and steroids.
3. Carbohydrates : These are usually below 5%. Carbohydrates present are mostly oligosaccharides and it occurs in two different combinations- glycolipids and glycoproteins.
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