Chapter 11
Biological Membranes:
Part 1
Membranes
Part 1 and 2 Learning Goals: To Know
– 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
Why are TEMs of membranes
always light in the middle and
dark on the sides?
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?
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
TetraSaccharides,
N-linked
Tetra-Saccharides,
O-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 Spacefilling 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.
Phospholipid Associated with Isolated Membrane
Proteins
Sheep Aquaporin
Fo Portion of V type Na-ATPase
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, monovalent 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;327:46-50
Published 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)