Membrane Structure & Function BSCI 420,421Lecture 14Oct 2002 Ghandi’s eyes looked out to sea. “When I was a boy, I used to sing a song in the temple: A true disciple knows another’s woes as his own. He bows to all and despises none.” 1.Membrane functions 2.Membrane structure 3.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 synthase b) Cytochrome p450s 4.Conduct electrical signals 5.Recognize and respond to molecules or surfaces a) Signal mol. Receptors b) 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 = redglycolipids = blue P-serine = green P-ethanolamine = yellow Sphingomyelin = 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 flippase enzyme selectively flips PS & PE to the cytosolic leaflet. (fig 12-59).

Freeze fracture TEM

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

Fluidity Allows Mixing of Membrane Proteins after fusion

Fluorescence Recovery After Photobleaching