Chapter 5: Structure and Function of Plasma Membranes Flashcards
Describe the phospholipid bilayer and its properties.
A double layer of phospholipids with hydrophilic heads facing outward and hydrophobic tails inward. Provides a flexible, selectively permeable barrier.
(Figure 5.1)
What is the fluid mosaic model?
The membrane is a dynamic structure with proteins embedded in or attached to the phospholipid bilayer. Components can move laterally.
(e.g., Figure 5.2)
Distinguish integral and peripheral proteins.
Integral: Embedded in the bilayer (e.g., channel proteins).
Peripheral: Loosely attached to the membrane surface (e.g., signaling proteins).
What role does cholesterol play in the membrane?
Stabilizes fluidity: reduces membrane rigidity at low temps and prevents excessive fluidity at high temps.
Compare passive and active transport.
Passive: No energy (ATP) required; follows concentration gradient (e.g., diffusion).
Active: Requires ATP; moves substances against the gradient (e.g., sodium-potassium pump).
Define facilitated diffusion. Example.
Passive transport using channel/carrier proteins.
(e.g., glucose uptake via GLUT transporters)
How does the sodium-potassium pump work?
Uses ATP to move 3 Na⁺ out and 2 K⁺ in per cycle, maintaining electrochemical gradients.
(Figure 5.10)
Contrast endocytosis and exocytosis.
Endocytosis: Cell engulfs substances (e.g., phagocytosis of bacteria).
Exocytosis: Vesicles fuse with membrane to expel contents (e.g., neurotransmitter release).
What is resting membrane potential?
The voltage difference (-70 mV in neurons) across the membrane, maintained by ion pumps and channels.
Define electrochemical gradient.
Combined effect of a chemical concentration gradient and electrical charge difference driving ion movement.
Role of glycoproteins/glycolipids?
Act as cell identity markers (e.g., blood type antigens) and assist in cell-cell recognition.
How do unsaturated fatty acids affect membrane fluidity?
Kinks in unsaturated tails increase fluidity, while saturated tails pack tightly, reducing fluidity.
What is cystic fibrosis? How is it linked to membrane dysfunction?
A genetic disorder caused by defective CFTR chloride channels, leading to thick mucus in lungs.
Describe the Frye-Edidin experiment.
Demonstrated membrane fluidity by fusing human and mouse cells; proteins mixed over time.
(Figure 5.3)
List 6 functions of membrane proteins with examples.
Transport (aquaporins).
Enzymatic activity (ATP synthase).
Signal transduction (hormone receptors).
Cell-cell recognition (MHC proteins).
Intercellular joining (tight junctions).
Attachment (integrins linking to cytoskeleton).
