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