MEMBRANES

Alberts et al., selections from Chapters 1, 10 and 15

Why are membranes so relevant (to deserve the first lecture)?
Signalling is usually across the membrane
Many important molecules are in the membrane

Get a good source of membranes
red blood cell ghosts - only has plasma membrane, flat cell with 2 sides,
Gorter and Grendel showed that there is enough lipid to make 2 layers
Lipids orient on the basis of hydrophobicity TRANSPARENCY Fig. 1-9 , p. 10
Bilayer (Robertson) or micelles TRANSPARENCY Fig. 10.3 , p. 479
Fluid mosaic model TRANSPARENCY Fig. 10-1, p. 477
2 dense lines in EM with osmium
outsides of membrane: glycoprotein, glycolipid, S-S (disulfide) bonds

Lipid biochemistry: TRANSPARENCY panel 2-4, pp. 54-55
(lots of information)
fatty acids :C18-stearic, C16, palmitic, C18-1 oleic
also shown are triglycerides, phospholipids, glycolipids, steroids
Phospholipids TRANSPARENCY Fig. 10.10, p. 483
phosphatidylcholine (lecithin)
phosphatidylethanolamine
phosphatidylserine [amino acid]
sphingomyelin w/ ceramide (based on serine) not glycerol
others
TRANSPARENCY Fig. 10-2 , p. 479
Double bonds make more fluid, note - double bonds more likely in #2 position
Glycolipids TRANSPARENCY Fig. 10-12 , p. 484
One pentameric subunit of cholera toxin (not the best-known one which ADP-ribosylates the alpha subunit of the alpha-stimulatury subunit of the heterotrimeric G protein) binds to membrane using the GM1 ganglioside as a receptor
Lack of a specific enzyme to break down GM is the cause of the famous genetic lysosomal "storage disease" common in Ashkenase Jews called Tay-Sach's disease
in animal, usually based on serine as sphingomyelin

Chloroform - methanol extract - aqueous and organic phases SLIDE
Separation on TLC SLIDE and autoradiogram

There is a special case for inositol lipids
TRANSPARENCY Fig. 15-29, p. 745
phosphatidylinositol inositol alcohol like sugar
PI -> PIP -> PIP2 (PI 4,5-bisphosphate) ->[via PLC (phospholipase C)] ->
IP3 (inositol trisphosphate)+ DAG (diacyl glycerol)
TRANSPARENCY Fig. 15-30, p. 746
-> IP3 (inositol 1,4,5-trisphosphate) and DAG (diacylglycerol)
IP3 involved in release of Ca2+ from non-mitochondrial intracellular membranes
DAG activates PKC (protein kinase C)
arachidonic acid is a special case with 4 double bonds
TRANSPARENCY Fig. 15-6, p. 725
arachidonic acid is oxidized to prostaglandins, etc.
One especially long and unsaturated fatty acid is DHA=docosahexaenoic acid=22-6

TRANSPARANCY Fig. 10-5, p. 480
artificial membranes - "black" (from bilayer)
can reconstitute with protein and study electrophysiologically

References:

E. Gorter and F. Grendel, On bimolecular layers of lipoids on the chromocytes of the blood, J. Exp. Med. 41, 439-443, 1925

J. D. Robertson, The membrane of the living cell, Scientific American 206, April 1962, 64-72

This page was last updated Dec. 19, 2001

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