Molecular Cell Biology Fifth 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 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 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: 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 Glycosylphosphosphatidylinositol sugar

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