1 - STRUCTURE AND FUNCTIONS OF CELL MEMBRANES

Lipids in cellular membranes

Phospholipids, Glycosphingolipids, and cholesterol

Function of lipids in cellular membranes (3)

1. Glycosphingolipids: Cell recognition and signaling.

2. Cholesterol: Membrane fluidity and raft formation

Lipids of outer leaflet

(Phosphatidyl) choline, sphingomyelin, and glycosphingolipids

Lipids of inner leaflet

(Phosphotidyl) Serine, Ethanolamine, and inositol

Membrane fluidity

Lateral movement

Types of membrane fluidity (2)

1. Lateral diffusion

2. Flip-flop (Transverse diffusion)

Lateral diffusion

Rapid, within same leafelet

Flip-flop (Transverse diffusion)

Slow, one leafelet to another

Factors of Membrane fluidity

Ratio of saturated to unsaturated fatty acids and cholesterol content

Enzymes that assist with phospholipid translocation (3)

1. Flippases

2. Floppases

3. Scrablases

Flippases

Use ATP to move phosphatidylethanolamine and phosphatidylserine from the outer to the inner leaflet

Floppases

Use ATP to move phospholipids like phosphatidylcholine and sphingolipids from the inner to the outer leaflet.

Scrablases

Move phospholipids down their concentration gradient, disrupting membrane asymmetry and signaling apoptosis.

Saturated fatty acids effects on fluidity

packed tightly, decreasing membrane fluidity. At room temperature, they are solid.

Unsaturated fatty acids effects on fluidity

increase membrane fluidity due to their kinked structure, which prevents tight packing.

Cholesterol effect on fluidity

Makes saturated regions less fluid and unsaturated regions more fluid. It also broadens temperature range

Lipid rafts

Domains of sat. FA, cholesterol, and proteins. Help with signals, curvature, and interactions

Fluid Mosaic Model

Describes the membrane as a dynamic bilayer of amphipathic lipids with embedded proteins that can move laterally. It emphasizes fluidity, diversity, and functionality.