Campbell and Reece, Chapter 8, plus some references back to earlier chapters
Get a good source of membranes: red blood cells (erythrocytes) from adult
human have only plasmalemma. Gorter and Grendel showed in1925 that there
was enough lipid to make two layers.
Put red blood cells into distilled water, they burst from hyposmotic shock
and become only "ghosts" - membrane only. TRANSPARENCY (Fig. 8.12
shows how animal vs plant cells react to hypertonic, isotonic and hypotonic
TRANSPARENCY (Fig. 8.1) shows hydrophobic vs hydrophilic aspect of polar
TRANSPARENCY (Fig. 5.12) [shown earlier] shows the chemical structure of
a polar phospholipid)
TRANSPARENCY (Fig. 7.6) 2 two dense lines in EM with osmium (Robertson)
TRANSPARENCY (Fig. 8.2) bilayer (Davson-Danielli)
TRANSPARENCY (Fig. 8.6) Fluid mosaic Singer and Nicolson
TRANSPARENCY (Fig. 8.7) Here is a famous membrane protein, rhodopsin, the
molecule we see with, and how 7 hydrophobic alpha helices fit into the hydrophobic
part of the membrane.
TRANSPARENCY (Fig. 8.3) Freeze fracture EM. Membrane is ripped in half,
and membrane proteins are shadowed.
Picture I made freeze
fracture replicas with this apparatus. Specimen is prepared, frozen to liquid
nitrogen temperature, put inside a vacuum, smashed with a razor, blasted
from an angle with a platinum gun (to shadow protein with electron dense
metal), blasted from above with a carbon gun (to hold replica together),
then the tissue is dissolved away.
Here, from my research,
is an example of how things look. Picture shows visual membranes in Drosophila.
High vitamin A has membranes full of protein (rhodopsin) while vitamin A
deprivation eliminates this protein.
Membrane lipids are composed of:
(1) Phospholipids such as phosphatidylcholine (lecithin)
I did some research on
the phospholipids of the Drosophila head. Using radioactively lbeled phosphate,
many different phospholipids are visualized after they have been separated
on a TLC (thin layer chromatography)
(3) Glycolipids such as one that accumulates in Tay-Sachs, a hereditary
lysosomal storage disease,1/30 Am. Jews carry, recessive, fatal at 6 mo
- 5 yr
The sugar groups of glycoproteins and glycolipids are on the outside of
TRANSPARENCY (Fig. 8.4) Double bonds make more fluid, cholesterol makes
It used to be thought that lipids just sit there. In the 1980's it became
clear that they turn over metabolically and that some products of membrane
lipid turnover are important mediators of intracellular signalling. This
is very fundamental and will come up repeatedly in biology.
TRANSPARENCY (Fig. 8.16) Diffusion
(1) Lipid makes a barrier to anything polar
(LATER: steroid hormones can go in)
(2) Channels (for ions, electrical conductances)
The 1991 Nobel Prize
in physiology and medicine was awarded to prize was awarded jointly to:
ERWIN NEHER and BERT SAKMANN for their discoveries concerning the function
of single ion channels in cells; in 1963 the prize was awarded jointly to:
SIR JOHN CAREW ECCLES , SIR ALAN LLOYD HODGKIN and SIR ANDREW FIELDING HUXLEY
for their discoveries concerning the ionic mechanisms involved in excitation
and inhibition in the peripheral and central portions of the nerve cell
membrane (in summary, the topic of ion channels is pretty fundamental).
(3) A large fraction of the cell's energy (ATP) goes to pumping ions (active
This creates an ion imbalance, sodium Na+ high outside cell, potassium K+
This gives rise to the membrane electrical potential (voltage) important
in nerve and muscle cells.
TRANSPARENCY (Fig. 8.15) how pump molecule uses ATP to make sodium and potassium
run in reverse, makes energy, motor - generator analogy ENERGY - Chap 9
phagocytosis - cell eating
pinocytosis - cell drinking
receptor mediated endocytosis - clathrin coated
Also holes in membranes from one cell to another are important:
(1) Gap junctions (animals)
(2) Plasmodesmata (plants)
TRANSPARENCY (Fig. 8.9) shows some other functions of membrane proteins
(1) in addition to transport,
(2) many enzymes are on the membrane
(3) receptors for hormones, neurotransmitters and developmental signals
are on the membrane.
(4) cells are joined by proteins
(5) cells communicate by proteins
(6) cells hook to extracellular proteins by proteins
This page was last updated 6/20/02
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