MCDB

1
CELL MEMBRANE Lecture 7 January 25th, 2006
2
Cell Membrane by EM

• Observation on electron microscope reveals an
  electron-dense bilayer separated by a clear layer
  (lipids).

3
Models for the Structure of the Plasma Membrane
Davson - Danielli
Singer and Nicolson
Current model modification of the Singer and
Nicolson model
4
Structure of the Cell Membrane by Freeze Fracture
5
The experimental model- Erythrocyte-
6
How to isolate membranes?
7
How to Study the Proteins of the Plasma Membrane
8
Proteins move freely within the lipid bilayer
Depending on the cell type and environmental
conditions, integral membrane proteins can
exhibit several types of mobility.
9
Many Cytoplasmic Proteins are Anchored in the
Plasma Membrane
10
Distribution of Integral Membrane Proteins
Analysis of membrane proteins by freeze -
fracture reveals that the distribution of
integral proteins is very heterogeneous
11
Structure of the Lipids in the Cell Membrane

• Membrane lipids form bilayers in water

Main lipids in plasma membranes 1.
Phosphoglycerdies 2. Sphingolipids 3.
Cholesterol
12
Temperature affects the lipid bilayer
Above the transition temperature, the molecules
of the lipid bilayer are free to move. Below the
transition temperature, the movement of molecules
is reduced and restricted.
13
LIPID RAFTS - SPHINGOLIPID AND CHOLESTEROL-DEPENDE
NT MICRODOMAINS IN THE PLASMA MEMBRANE
14
A MODEL FOR LIPID RAFTS IN MIRR SIGNALING
15
AMOUNT AND CONTENT OF RAFTS IS CELL -DEPENDENT
16
IL-2Ra
CLUSTERING EFFECT OF PATCHING ON
CTB-LABELED RAFTS IN HUMAN T-CELLS
IL-2Rb
IL-2Rg
IL-15Ra
17
SPATIAL AND TEMPORAL CONTROL OF SIGNALING THROUGH
LIPID RAFTS A - Extracellular signals B - Local
recruitment and accumulation of lipid rafts C -
Rac1-GTP targets to the lipid rafts D - Feedback
loop that sustains polarized signaling
Signal
A
GF
ECM
Preferred recruitment
B
Signal
D
Positive Feedback loops In signaling
C
Rac1-GTP
18
DYNAMICS OF SIGNALING COMPONENTS IN AND OUT OF
RAFT DOMAINS
PROTEIN PALMITOYLATION
DEPALMITOYLATION
PALMITOYLATION
RECYCLING ENDOSOME
19
DYNAMICS OF SIGNALING COMPONENTS IN AND OUT OF
RAFT DOMAINS
SEQUESTRATION TO CAVEOLAE
Caveolae
Caveolin-Pi
Caveosome
20
DYNAMICS OF SIGNALING COMPONENTS IN AND OUT OF
RAFT DOMAINS
IMMOBILIZATION THROUGH CYTOSKELETON
ERM ACTIVATION
SIGNALING