Download Plasma membrane Affect shape and function Anchor protein to the

Harvey Lodish • Arnold Berk • Paul Matsudaira •
Chris A. Kaiser • Monty Krieger • Matthew P. Scott •
Lawrence Zipursky • James Darnell
Molecular Cell Biology
Fifth Edition
Chapter 5:
Biomembranes and Cell Architecture
Copyright © 2004 by W. H. Freeman & Company
Plasma membrane
1. Affect shape and function
2. Anchor protein to the membrane
3. Modify membrane protein activities
4. Transducing signals to the cytoplasm
Lipid Bilayer
1. Impermeable barrier prevent diffusion
of water soluble solute
2. Membrane protein mediate transport of
specific molecule
3. Maintained by hydrophobic interaction
Van der
waal
interaction
between
membranes
RBC
Smooth and
flexible
Long , slender extension
Multiple layers of modified plasma membrane: formed by adjacent glial cells
The faces of cellular membrane
1. Internal faces
surface orient toward the interior of
the compartment
2. External faces
the surface presented to the
environment
Chloroplast in
plants
磷酸甘油酯
i.e.plasminogen
Acyl group:
c16 or c18,
0, 1 or 2 double bond
choline head膽鹼
鞘酯
sphingomyelin
glucosylcerobroside
Hydrocarbon chain
Four ring hydrocarbon
amphipathic
FRAP:
Fluorescent Recovery After Photobleaching
Most lipids and proteins are laterally mobile in biomembrane
Lipid composition influence physical properties
of membrane:
1. Different composition of organs
2. Specialized membrane function
i.e. apical surface if intestinal lumen
sphingolipids: phosphoglycerides: cholesterol
basolateral
apical
0.5
1
1
1
1
1
3. Affects membrane fluity
a. short C-H chain are more fluid
b. kinks in C-H: less stable
Long saturated fatty
acyl chain
heat
Decreased thickness
4. Influence thickness of membrane
5. Local curvature
Larger head
Smaller head
bilayer enriched with PC in the
exoplasmic leaflet and with PE in the
cytoplasmic face would cause the
natural curvature
Membrane asymmetry Affects:
1. Enzyme cleavage
phospholipase cleaves phospholipids at
exoplasmic sides
 cytosolic sides are resist to phospholipase
cleavage
Cleave
phospholipid
at cytosolic
side
2. Membrane based functions
i.e. signal transduction pathway of
phosphotidyl inositol
Cleavage by phospholipase C
PI + Diacylglycerol( DAG)
Activation of signal transduction pathway
i.e. phosphotidyl serine
stimulation of platelate by serum
translocate to exoplasmic face
activate enzyme for blood clotting
Lipid Raft
micro domain of cholesterol, sphingolipids and
certain membrane protein
GM1: glycosphingolipids
PLAP: placental alkaline phosphatase
TfR: transferrin receptor
Three categories of membrane protein
1. Integral membrane protein( transmembrane
protein)
a. exoplasmic domain
cytosolic domain
hydrophilic
b. Membrane spanning domain: hydrophobic
c. glycosylated
2. Lipid anchored membrane protein
covalently bound to lipid
3. Peripheral membrane protein
bound to membrane by interaction with
integral membrane protein



Glycophorin A: a typical single pass transmembrane
protein
-helices
Binding of Arg or Lys to negatively charged head of phospholipid
-helices:
20-25 hydrophobic amino acids
Interact with fattyacyl of lipid by van- der-waals
G protein:
7-multipass
bacteriorhodopsin
retinal
Porin
Trimric tramsmembrane
protein
Barrel shape subunit with ßsheet wall and hydrophilic
center
aliphatic and aromatic side
chain position the protein on
the membrane
Anchoring of plasma membrane proteins to the
bilayer by covalently linked hydrocarbon group
1. anchor by fatty acyl group
2. Anchor by unsaturated fatty acid to cyctein at
or near C terminal
3. GPI anchoring
lipid anchor on membrane is glycosyl
phosphotidyl inositol( GPI)
sugar
Gly
C14 or C16
Glycosylphosphosphatidylinositol
Cys
C15 or C20
All transmembrane proteins and glycolipids
are asymetrically oriented in the bilayer
Motility of membrane protein
1. Float freely
2. Immobile
3. Anchored by cytoskeletal protein
PH ( pleckstrin homology domain)
Interfacial binding surface and mechanism of action of
phospholipase A2
Effects of external ion concentration on water
flowacross the plasma membrane of an animal
cells