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Chapter 7 Membrane Structure and Function - Coggle Diagram
Chapter 7 Membrane Structure and Function
Cellular Membranes are Fluid Mosaics
Fluidity of Membranes
Phospholipid bilayer: Amphipathic (hydrophilic heads, hydrophobic tails).
Lateral movement: Frequent.
Flip-flop: Rare.
Fluidity affected by:
Temperature: Lower temps = less fluid
Unsaturated fatty acids: Increase fluidity.
Cholesterol: Maintains fluidity by preventing tight packing at low temps, restrains movement at high temps.
Membrane Lipid Composition
Varies by species, organelle, and function.
Adaptation to environments (e.g., cold = more unsaturated fats).
Membrane Proteins
Integral proteins: Penetrate bilayer (often transmembrane).
Peripheral proteins: Loosely bound to membrane surface.
Functions:
Transport
Transport
Signal transduction
Cell-cell recognition
Intercellular joining
Attachment to cytoskeleton and ECM
Carbohydrates in Membranes
Glycolipids and glycoproteins
Involved in cell-cell recognition
Located on extracellular side of membrane
Membranes and Selective Permeability
Definition
Membranes allow some substances to pass more easily than others.
What can cross easily?
Nonpolar molecules (e.g., O₂, CO₂)
Small uncharged polar molecules (e.g., H₂O to some extent)
What needs help crossing?
Large polar molecules
Ions (e.g., Na⁺, K⁺, Cl⁻)
Passive Transport
Diffusion
Movement down concentration gradient
No energy required
Osmosis
Diffusion of water across a selectively permeable membrane
Tonicity:
Isotonic: No net water movement
Hypertonic: Water leaves cell (shrinks
Hypotonic: Water enters cell (swells)
Facilitated Diffusion
Transport proteins help molecules cross
Channel proteins (e.g., aquaporins)
Carrier proteins
Still passive – no energy used
Active Transport
Requires Energy (ATP)
Moves substances against concentration gradient
Carrier Proteins Involved
Carrier Proteins Involved
3 Na⁺ out, 2 K⁺ in
Maintains electrochemical gradient
Electrochemical Gradient
Membrane potential: voltage across membrane
Ions move due to both concentration and electrical forces
Cotransport
Active transport of one solute indirectly drives another
Example: Proton pump + sucrose-H⁺ cotransporter
Bulk Transport
Exocytosis
Vesicles fuse with membrane to release contents outside cell
Endocytosis
Cell takes in materials by forming vesicles
Phagocytosis: "Cell eating"
Pinocytosis: "Cell drinking"
Receptor-mediated endocytosis: Specific molecule uptake
Additional Notes on Related Processes
Protein Transport and Processing
Begins in ribosomes (free or bound)
Proteins enter ER → Golgi apparatus
Sorted and shipped via vesicles
Membrane proteins are embedded during this process
Lipid Metabolism
Smooth ER synthesizes lipids
Lipids added to membranes or transported via vesicles
Important in maintaining membrane fluidity and composition