1. The fluid-mosaic model of membrane structure
Polysaccharide attached to protein forming a glycoprotein
Phospholipid bilayer
Protein
Cholesterol

2. The structure of the plasma membrane
“FLUID” – the molecules can move within the membrane
“MOSAIC” – other molecules eg proteins are embedded within the phospholipid bilayer

3. Fluid Mosaic Model Branching carbohydrate portion of protein which
acts as an antigen
Glycolipid
Hydrophilic heads of phospholipid molecules
Protein molecule lying on surface
Pore
Hydrophilic tails
of phospolipid molecules
Protein molecule spanning the phospolipid bilayer
Protein molecule
partly embedded

4. MEMBRANE PROTEINS Can be:
Extrinsic – on the surface eg receptor proteins for hormones, cell recognition molecules (eg glycoproteins)

5. Or can be:
Intrinsic – span the membrane between the outside and inside of the cell eg carrier proteins/channel proteins

6. Both these types of proteins are globular proteins with a specific shape which only fits molecules with a complementary shape eg insulin receptors only fit insulin, sodium channels only allow sodium through.

7. Electron micrograph of the plasma membrane of two adjacent epithelial cells
glycoprotein coat
plasma membrane

8. PHOSPHOLIPIDS
These are polar molecules with hydrophilic (‘water loving’) phosphate heads (PO4-) and hydrophobic (‘water hating’) fatty acid tails.

9. These arrange themselves in a bilayer with the hydrophilic heads on the outside and the hydrophobic tails on the inside
THINK!!!!
Why do they arrange themselves this way?

10. Fluid – Mosaic Model (Singer & Nicholson, 1972)
Carbohydrate attached to a lipid : glycolipid
Carbohydrate attached to a protein : glycoprotein
lipid bilayer
hydrophobic regions of protein
hydrophilic region of protein
hydrophilic channel, acts as a pore through which ions & certain polar molecules may pass
EXT
INT
In this model the lipid bilayer remains unchanged as the unit membrane, but it is regarded as a dynamic structure in which proteins can float in the lipid, some moving about freely, while others are fixed in position.

11. The phospholipids and proteins regulate the movement of substances through the membrane (membrane is selectively permeable)

12. The phospholipid molecules allow small, uncharged or lipid-soluble molecules through (O2, CO2, H2O)
Larger, charged and water soluble molecules can only cross the membrane via the carrier and channel proteins (e.g. Glucose: C6H12O6 and ions such as Na+, Cl-, K+).