Cell Membrane Structure and Functions

Cell Membrane Structure

• Composed primarily of proteins (55%), lipids (42%), and carbohydrates (3%).
• Major lipid components include phospholipids (25-35%), cholesterol, glycolipids.
• Proteins can be either peripheral (on the surface) or integral (embedded within the membrane).

Cell Membrane Properties

• Consists of two layers, providing flexibility.
• Selectively permeable, allowing some substances to pass through while blocking others.
• Carbohydrates attached to the membrane act as recognition sites, aid in self-differentiation, and contribute to cell adhesion.

Cell Membrane Functions

• Serves both physical (protection) and physiological (transport, communication) roles.
• Facilitates transport mechanisms including diffusion, osmosis (water transport), filtration (salt transport), and active transport (e.g., Na+-K+ pump).
• Engages in processes like pinocytosis (cell drinking) where dissolved proteins are taken into the cell via vesicles.
• Participates in endocytosis (exocytosis) where large particles are transported into the cell within vesicles, further dividing into smaller components like hormones and neurotransmitters.
• Utilizes phagocytosis (cell eating) to engulf bacteria, dust, etc. within a vesicle called a phagosome.
• Employs vesicles (endosomes) to release substances into the cytoplasm.

Cell Membrane Characteristics

• Extremely thin and elastic.
• Exhibits semi-permeability, allowing selective passage of substances.
• Demonstrates dynamic structure, constantly changing and adapting.
• Facilitates transport of gases and nutrients (e.g., O2, CO2, lipid-soluble substances, fatty acids, glucose).