1. Membranes
Topic 1.3

2. Cell membrane structure

3. Membrane Structure Phospholipid bilayer Hydrophobic Hydrocarbon Tail
Hydrophilic Phosphate Head
Cholesterol
Glycoproteins
Integral proteins
Peripheral Proteins

4. Cell Membrane Theory
Gorter and Grendel extracted phospholipids from red blood cells and deduced that the membrane had 2 layers (bilayer)
It did not explain where the proteins were
Davson and Danielle deduced that the proteins were adjacent to the lipids on either side

5. Davson and Danielli Saw 2 dark lines with a lighter band in between
Proteins usually look dark on micrographs and lipids look lighter

6. Cell Membrane Theory Singer and Nicolson (1966)
Proteins occupy a variety of positions in the membrane
They are also capable of moving their location
Like tiles in a mosaic
Fluid-Mosaic Model

7. Falsification of Davson and Danelli
Membrane proteins were found to be different sizes and shapes. It is unlikely they would form a continuous layer on top of the membranes
Freeze etching showed proteins dsipearsed throughout the membrane
Fluorescent anti-body tagging of membrane proteins supported the freeze etching results

8. Falsification of Davson and Danelli

9. Phospholipids Partly hydrophilic and hydrophobic (amphipathic)
Phospholipid phosphate groups are attracted to water where as their hydrocarbon tails are not.
Hydrocarbon tails are attracted to one another just as the phosphate heads are attracted to other phosphate heads.
This attraction makes for a strong but fluid membrane.

10. Structure of phospholipids

11. Fluid Mosaic Model Phospholipids in membranes are in a fluid state.
This allows membranes to change shape.
Proteins are seen to be sporadically placed in the membrane.
Proteins float within the membrane as well as on the surface.

12. Membrane Proteins 4.Cell to Cell communication:
1. Hormone Binding Site:
Site exposed on the outside of the membrane allows one specific hormone to bind thus transmitting a signal to the inside of the cell.
2. Enzymes:
Enzymes located in the membranes either catalyze reactions inside or outside the cell. (this depends on where their active site is)
3. Cell Adhesion:
Forms tight junctions between cells and tissues.
4.Cell to Cell communication:
- Cell receptors receive signals via hormones or neurotransmitters

13. Membrane Proteins 5. Passive Transport Protein:
Channels or passages through the center of the membrane proteins. Each channel is specific for certain substances.
6. Protein Pumps for Active Transport:
Pumps release energy from ATP and use it to move specific substances across the membrane.

14. Membrane proteins

15. Cholesterol in membranes
Found in animal cells
Types of lipid called a steroid
Mostly hydrophobic so it attaches to the lipid portion of the membrane
It does have a small hydrophilic portion that is attached to the phosphate head
It is usually found between phospholipids

16. Cholesterol in membranes

17. Role of cholesterol in membranes
Controls the fluidity of the membrane
Too fluid and it cannot control what comes in/out
Not fluid enough and it restricts cell movement
Cholesterol disrupts the packaging of the hydrocarbon tails (so not so rigid)
Reduces the permeability of some ions
Show video