Cell Membrane & Specializations Lecture PDF

Molecular structure plasma membranes consist mainly of: Lipids (40%). Proteins (50%). Carbohydrates (10%). Lipids (phospholipids + cholesterol) double layer of phospholipids (hydrophilic polar heads outwards and hydrophobic nonpolar tails inwards). Membrane proteins (50%): Present within the lipid b...

Molecular structure plasma membranes consist mainly of: Lipids (40%). Proteins (50%). Carbohydrates (10%). Lipids (phospholipids + cholesterol) double layer of phospholipids (hydrophilic polar heads outwards and hydrophobic nonpolar tails inwards). Membrane proteins (50%): Present within the lipid bilayer 1- Integral (intrinsic) proteins: - pass through the thickness of membrane. - incorporated within the lipid bilayer. 2- Peripheral (extrinsic) proteins: - Loosely attached to surface. the Carbohydrates (Cell coat) present on external surface of cell membrane. consists mainly of glycoproteins and of some glycolipids. Functions: protection, and adhesion. Functions of cell membrane: 1- protection of cell. 2- controls movements of substances into or out of the cell. I- Permeability: passive or active II- Endocytosis (phagocytosis or pinocytosis) & exocytosis: Ions and small molecules From this diagram, can you differentiate between passive and active transport? Endocytosis : large molecules (as bacteria) are transported into the cell by endocytosis. Exocytosis: macromolecules as secretory vesicles transport their content outside the cell by exocytosis Types of endocytosis: 1- Phagocytosis (cell eating) 2- Pinocytosis (cell drinking) Specializations of cell membrane: 1- Microvilli: long finger-like projections on the surface e.g. absorptive cells of small intestine to increase the surface area. 2- Cilia: hair-like processes on the surface of cells e.g. respiratory tract. They move in one direction to push away mucus and harmful materials. 3-Flagella: resemble cilia in general structure but are longer and present only in spermatozoa. 4- Cell junctions: they connect adjacent cells together and are of 3 types: I- Tight junction: the two cell membranes fuse and the intercellular space is absent (e.g. intestinal absorptive cells). II- Gap junction: narrowing of the intercellular space to become 2 nm (normally 20 nm) (e.g. cardiac muscle). It is communicating junction. III- Desmosome: the intercelluar space is normal (20 nm) It is a type of adherens junction.