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Dr Pradeep Kumar Professor, Physiology KGMU The Plasma Membrane – a Phospholipid Bilayer Components of Plasma Membrane Lipids ~50% 1) Phospholipids (75%) 2) Cholesterol (20%) 3) Glycolipds (5%) Proteins ~50% 1) Peripheral (Associated) 2) Integral (Membrane Spanning) 3) Glycoproteins Isolate the cell’s contents from the external environment Regulate traffic in and out of the cell Communicate with other cells The phospholipid bilayer 1. Impermeable to water-soluble and polar molecules, ions 2. Permeable to small and nonpolar molecules 3. Lipids oriented with polar heads facing out tails (hydrophobic) head (hydrophilic) extracellular fluid (watery environment) phospholipid hydrophilic heads hydrophobic tails bilayer hydrophilic heads cytoplasm (watery environment) Membranes are “fluid mosaics” with proteins embedded in or attached to the membrane Proteins can move within the fluid lipid bilayer extracellular fluid (outside) recognition protein receptor protein transport protein binding site phospholipid bilayer carbohydrate phospholipid cholesterol protein filaments cytoplasm (inside) 1. Transport proteins ◦ regulate the movement of water-soluble molecules across the membrane Ion Channel proteins, Pumps, Receptors Carrier proteins, Enzymes, Cell adhesion Molecules 2. Receptor Proteins ◦ trigger cellular response when specific molecules bind to them Nervous system Endocrine system Passive transport is a function of molecular size, lipid solubility, and size of the concentration gradient 1. Simple diffusion 1 A drop of dye is placed in water. drop of dye pure water 2 Dye molecules diffuse into the water; water molecules diffuse into the dye. 3 Both dye molecules and water molecules are evenly dispersed. (a) simple diffusion (extracellular fluid) (cytoplasm) Passive transport…(cont.) ◦ 2. • • • Osmosis a. Isotonic b. Hypertonic c. Hypotonic 10 micrometers (a) isotonic solution equal movement of water into and out of cells (b) hypertonic solution net water movement out of cells (c) hypotonic solution net water movement into cells Passive transport…(cont.) ◦ 3. Facilitated diffusion (b) facilitated diffusion through a channel ions proteins forming permanent hydrophilic channel channel protein (c) facilitated diffusion through a carrier amino acids, sugars, small proteins carrier protein Carrier protein has binding site for molecule. (extracellular fluid) (cytoplasm) Molecule enters binding site. Carrier protein changes Carrier protein shape, transporting molecule resumes original shape. across membrane. Energy-requiring transport 1. Active transport • Ion gradients and energy production 2. Endocytosis 3. Exocytosis Primary Active Transport: The Na+/K+ Pump Antiport Secondary Active (Indirect): e.g., Na+/Glucose transporter Symport (extracellular fluid) transport protein ATP ATP Transport protein recognition Transport protein uses binding Transport protein resumes original site energy from ATP to site binds ATP and Ca2+ change shape and move shape. 2+ Ca . (cytoplasm) ion across membrane. (a) pinocytosis (extracellular fluid) 1 2 3 vesicle containing extracellular fluid (cytoplasm) cell (b) phagocytosis food particle pseudopod 1 2 3 particle enclosed in vesicle Thank You