Cell Membrane

Haixu TangSchool of Informatics

Membrane Lipids Are Amphipathic Molecules

hydrophilic and hydrophobic molecules interact differently with water

Packing arrangements of lipid molecules

The spontaneous closure of a phospholipid bilayer

Phospholipid mobility

The other composition of membraneCholesterol and glycolipids

It inhibits possible phase transitions: (1) decreases the permeability of the bilayer to small water-soluble molecules; (2) prevents the hydrocarbon chains from coming together and crystallizing.

Cholesterol

Glycolipid

Four major phospholipids in mammalian plasma membranes

Cell wall

Lipid raft

The asymmetrical distribution of phospholipids and glycolipids

Functions of phospholipids in cell signaling

Membrane proteins

Membrane attachment of Water soluble proteins

Transmembrane polypeptide chain crossing the lipid bilayer

Using hydropathy plots to localize potential -helical membrane-spanning segments

-barrels (occasionally)

Solubilizing membrane proteins with a mild detergent

Two detergent

Reconstituting functional membrane

protein system

Red cell membrane

Preparing red cell ghosts

SDS polyacrylamide-gel electrophoresis pattern of the proteins in the human red

blood cell membrane

Three major ways of proteins association with membranes

• Noncovalently Associated with the Cytosolic Side: Spectrin

• Extends Through the Red Blood Cell Lipid Bilayer as a Single a Helix: Glycophorin

• Multipass Membrane Protein: Band 3 protein

Spectrin: cytoskeleton protein

Spectrin-based cytoskeleton

Glycophorin: single pass membrane proteins

Band 3: Anion Transporter

The polypeptide chain (about 930 amino acids long) is thought to extend across the bilayer 12 times.

Photosynthetic reaction center

The Cell Surface Is Coated with Sugar Residues

Carrier proteins and channel proteins

A typical ion channel

The gating of ion channels

Potassium ion gate

Passive and active transport

Three ways of driving active transport