Molecular Cell Biology Fifth Edition Chapter 5: Biomembranes and Cell Architecture Copyright © 2004...
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Transcript of Molecular Cell Biology Fifth Edition Chapter 5: Biomembranes and Cell Architecture Copyright © 2004...
Molecular Cell BiologyFifth Edition
Chapter 5:Biomembranes and Cell Architecture
Copyright © 2004 by W. H. Freeman & Company
Harvey Lodish • Arnold Berk • Paul Matsudaira • Chris A. Kaiser • Monty Krieger • Matthew P. Scott •
Lawrence Zipursky • James Darnell
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
Acyl group:
c16 or c18,
0, 1 or 2 double bond
i.e.plasminogen
鞘酯 sphingomyelin
glucosylcerobroside
choline head膽鹼
Four ring hydrocarbon
amphipathic
Hydrocarbon chain
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 0.5 1 1
apical 1 1 1
Long saturated fatty acyl chain
heat
3. Affects membrane fluity
a. short C-H chain are more fluid
b. kinks in C-H: less stable
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
Cleavage by phospholipase C
phosphotidyl inositol
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 domainhydrophilic
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 ß-
sheet 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)
Gly Cys
C14 or C16 C15 or C20
Glycosylphosphosphatidylinositolsugar
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