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Membrane Structure and Function - Coggle Diagram
Membrane Structure and Function
Structure of the Cell Membrane
Membrane Composition and Structure
Membrane = phospholipid bilayer + proteins + carbohydrates
Amphipathic phospholipids: hydrophilic heads, hydrophobic tails
Proteins: float in bilayer
Membrane held by weak hydrophobic interactions
Membrane Fluidity
Depends on temperature & lipid type
Unsaturated fats → more fluid
Saturated fats → less fluid
Cholesterol: stabilizes fluidity
Warm temp: limits movement
Cool temp: prevents packing
Membrane Proteins
Peripheral proteins: on surface
Integral proteins: penetrate bilayer
Transmembrane proteins span entire membrane
Anchored by cytoskeleton or extracellular matrix
Membrane Carbohydrates
Short, branched chains → attached to lipids (glycolipids) or proteins (glycoproteins)
Used for cell recognition
Make membrane asymmetrical
Function and Transport Across Membranes
Selective Permeability
Hydrophobic molecules (O₂, CO₂) → pass easily
Hydrophilic molecules (ions, sugars, H₂O) → need transport proteins
Passive Transport
Diffusion: movement down concentration gradient
Osmosis: diffusion of free water
Isotonic → no water movement
Hypotonic → water enters cell
Hypertonic → water leaves cell
Facilitated Diffusion
Channel proteins: provide tunnels
Carrier proteins: change shape to move molecules
Gated channels: open/close by electrical or chemical signal
Active Transport
Moves solutes against gradient
Sodium-potassium pump: 3 Na⁺ out, 2 K⁺ in
Maintains membrane potential
Inside negative, outside positive
Bulk Transport
Exocytosis: vesicles fuse with membrane → release materials
Ex: insulin secretion
Endocytosis: cell takes in material by forming vesicle
Phagocytosis: “cell eating”
Pinocytosis: “cell drinking”
Receptor-mediated: specific molecules bind receptors
Cotransport
The “downhill” diffusion of one solute drives the “uphill” transport of another.
Plant example: H⁺ gradient drives sucrose uptake.