Download module 2 2.1.5 biological membranes student version

2.1.5 Biological Membranes
What are the functions of the
cell surface membrane?
1.
2.
3.
4.
5.
6.
The cell surface membrane
structure
 75% phospholipid with some proteins,
cholesterol and polysaccharides.
 About 7 nm thick.
 Is a phospholipid bilayer.
 The phosphate group is hydrophilic (water-loving) and
turns towards the solution. The fatty acids are
hydrophobic (water-hating) and turn away from the
solution. They form a mirror image of each other.
(a) Phospholipid molecule enlarged and (b)
layer of phospholipids at the
surface of water
A phospholipid bilayer
Week 3
The Fluid mosaic theory




Proposed in 1972 by Singer & Nicholson.
There are several proteins in the bilayer.
Intrinsic proteins span the whole bilayer.
Extrinsic proteins are only found on either the inner or
outer surface.
 H bonds between proteins and phospholipids keep the
membrane relatively stable.
 Glycolipids are also present and important in cell-cell
recognition.
The fluid mosaic model
The fluid mosaic model
The fluid mosaic model
Factors which increase
Factors which decrease
fluidity of the membrane fluidity of the membrane
More unsaturated fatty
More saturated fatty acids
acids in the membrane
in the membrane
Shorter fatty acid tails
Longer fatty acid tails
Less cholesterol in the
membrane (plant cells
rarely have cholesterol)
Increases in temperature
More cholesterol in the
membrane (animal cells
about 20%)
Lower temperatures
Factors that affect membrane
structure - Temperature
Factors that affect membrane
structure - Solvents
The fluid mosaic model
 Entry into and out of cells is controlled by membrane
proteins.
 Carrier proteins and channel proteins allow the
transport of ions and other molecules. They can also
regulate concentrations of these on either side of the
membrane.
 Some use active transport (using energy from ATP) to
transport against a concentration gradient.
The fluid mosaic model
The fluid mosaic model
There may also be:
 Receptor proteins, which are important in binding
extra cellular molecules such as hormones.
 Membrane enzymes such as ATPase.
 Glycoproteins; protein & polysaccharide complexes
which act as antigens (cell surface markers).
Cell Signalling and Cell
Recognition
 Using OCR BIO AS books P.19-21, ‘Blocking Viruses
With Synthetic Receptors’ article and OCR AS Bio
sheet on Cell Signalling.
 Write your own summary on cell signalling and
recognition.
 Explain the term cell signalling and the role of
membrane-bound receptors as sites for hormones and
drugs to bind with .
Carry out
Practical Activity 5.2 Factors
Affecting Membrane Structure