biological membranes: part 1 chapter 11. membranes –the function of biological membranes –the...
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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)