Biological Membranes:

Part 1

Chapter 11

Membranes

– The function of biological membranes – The structure and composition membranes and

their molecules– Dynamics of membranes– Structure and function of membrane proteins– Transport across biological membranes

Part 1 and 2 Learning Goals: To Know

50 – 80 Å Thick

EOC Problem 5 has to do with the length of a fatty acid: how does this play into the thickness of this membrane?

Why are TEMs of membranes always light in the middle and dark on the sides?

Cells Are Loaded with Membranes

What’s the answer to the previous thought question?

Major Membrane Lipids

Membrane Lipid Composition – Rat Hepatocyte

Fluid Mosaic Model

Lipids aggregate into structures in water

• Structures formed depend on:– type of lipid– concentration

• Micelles• Liposomes• Bilayers

Lipids in Water

EOC Problem 3 … Number of SDS moleucles/micelle. You will need to calculate the MW of dodecyl-sulfate.

Asymmetric Distribution of

P-lipids in Erythrocyte Membrane

Membrane composition and asymmetry

Membrane Asymmetry Derived in ER

Functions of Proteins in Membranes

• Receptors: detecting signals from outside– Light (opsin)– Hormones (insulin receptor)– Neurotransmitters (acetylcholine receptor)– Pheromones (taste and smell receptors)

• Channels, gates, pumps– Nutrients (maltoporin)– Ions (K-channel) – Neurotransmitters (serotonin reuptake

protein)

• Enzymes– Lipid biosynthesis (some acyltransferases)– ATP synthesis (F0F1 ATPase/ATP synthase)

Extraction of Membrane Proteins

Glycophorin – Transmembrane Protein

Tetra-Saccharides, O-linked

Tetra-Saccharides, N-linked

Six Types of Integral Membrane Proteins

Bacteriorhodopsin

Bacteriochlorophyll – Reaction Center

Chlorophylls in Red

Great Illustration of Phospholipid as a Fluid

Sec A (chaperone) in blue ribbon. Cytoplasmic side with ATP (bright light)

Sec YE in Cream Space-filling cut away to show channel

Transported protein in red thread

Another Great Illustration of

Phospholipid as a Fluid

G Protein – major signaling protein, next Chapter.

Sheep Aquaporin Fo Portion of V type Na-ATPase

Phospholipid Associated with Isolated Membrane Proteins

Hydropathy Plots

Remember Hydropathic Index?

Non Polar R groups have Positive Hydropathic Indices Y and W are negative

Polar Amino Acids have Negative Hydropathic Indices

Hydropathy Index Calculated from a Moving -Window of 7 to 20 Amino Acids

Transmembrane Proteins – Positions of Y and W.

Polar R – groups are Blue

Y is Orange W is Red

Membrane Spanning Regions can also be Beta-Barrel Structure

Another Great Illustration showing the Membrane as a

Fluid

Surface of a B-cell showing the B-cell Receptor (purple, mono-valent IgM) binding to an HIV particle.

Sided Proteins Anchored by Fatty Acids (Inside)

Membranes can transition from Gels to Fluids

a. Gel State b. Liquid Ordered

Liquid Disordered

Measuring Rate of Phospholipid Mobility

Membrane Lipid Movement over 56 msec

EOC Problem 6 involves temperature effects on lateral diffusion in membranes.

Some Membrane Proteins Have Cytoskeleton Restricted Movement

Atomic Force Microscopy

AFM Aquaporin from E. coli – Outside View

Rafts and GPI-linked Proteins

Rafts and Sea

AFM Detects “Rafts” of Sphingolipids + Cholesterol

Hierarchy of raft-based heterogeneity in cell membranes

D Lingwood, K Simons Science 2010;327:46-50Published by AAAS

Integral Membrane Proteins Involved in Cell-Cell Communication

Membrane Fusion Events,

An Overview

To do this, proteins have to get two membranes very close together so they touch.

Caveolin Dimers form Caveloa

Three Models for Protein-Induced Curvature

Types of Endocytosis

Influenzia Virus Must “Uncoat” in Cytoplasm

Things to Know and Do Before Class

1. The major and minor membrane phospholipids.

2. Transmembrane protein structures and how they are held into the membrane.

3. Peripheral membrane proteins and how they are attached to the membrane.

4. Membrane temperature driven transitions.

5. What AFM tells us about membrane structure.

6. Membrane fusions + formation of endosomes.

7. EOC Problems: 3, 5, 6 (Hint need to calc SDS mole wt 288 Daltons)