Membrane Structure & Function

BSCI 420,421 Lecture 14 Oct 2002

Ghandi’s eyes looked out to sea. “When I was a boy,I used to sing a song in the temple: A true discipleknows another’s woes as his own. He bows to all anddespises none.”

1. Membrane functions2. Membrane structure3. Membrane fluidity

Membranes serve a wide variety of functions

1. Barriers to separate cells from environment(plasma membrane)and one compartment from another (organelle membranes)

2. Transport – Passive, active, and vesicular transport

3. Sites for enzyme systems, e.g.a) ATP synthaseb) Cytochrome p450s

4. Conduct electrical signals

5. Recognize and respond to molecules or surfacesa) Signal mol. Receptorsb) Immune response to antigens

3 views of a membrane

TEM of RBC thin section Model of membrane structure

A common phospholipid – Phosphatidyl choline

Hydrophilic

vs.

Hydrophobic

Molecules in water

Lipid rafts form that are rich in Sphingolipids, cholesterol.And certain membrane proteins

P-choline = red glycolipids = blueP-serine = greenP-ethanolamine = yellowSphingomyelin = brown

Asymmetry of membrane lipids

Basis of lipid asymmetry:

Synthesis of membrane lipids occurs on the ER.After they are delivered to the PM, a flippaseenzyme selectively flips PS & PE to the cytosolicleaflet. (fig 12-59).

Freeze fracture TEM

FF 0f RBCs P and E faces with protein particles visible

FluidityAllows Mixing ofMembrane Proteins afterfusion

Fluorescence Recovery After Photobleaching