1. 2.4 Membrane Structure

2. Phospholipid bilayer Flexible, adaptable, in motion
Selectively permeable
“Controlled entry”
Small, hydrophobic
Hydrophobic fatty acid tails repel water and form the middle layer
Hydrophilic phosphate heads attract water and form outer layers

3. Why are membranes important?
Membranes define compartments
Membrane proteins control traffic
Membranes are fluid

4. 1.4 Membrane Transport
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5. Davson-Danielli Sandwich Model (1930)
Proposed layers of protein adjacent to the phospholipid bilayer
Evidence
Proteins appear dark in electron micrographs and phospholipids appear light

6. Singer-Nicolson Fluid Mosaic Model
Evidence
1. Freeze etched images of the center of membranes was interpreted as trans membrane proteins
2. Improvements in biochemical techniques led to discovery of new membrane structures. Membranes were found to be varied in size and shape.

7. Mini Research on Transport
Topics: Endocytosis & Exocytosis, Simple/facilitated diffusion & Osmosis, Active Transport
In your presentation, explain:
What is it?
What kind of materials are transported across the membrane, and how?
Give a specific example of materials transported across the membrane.

8. Cholesterol
Lipids move laterally in a membrane, but flip-flopping across the membrane is rare.
Unsaturated hydrocarbon tail of phospholipids have kinks that keep the molecules from packing together, enhancing membrane fluidity.
Cholesterol reduces membrane fluidity by reducing phospholipid movement at moderate temperatures but it also hinders solidification at low temperatures.

9. 2.4.4 Passive transport: 1. Simple Diffusion
Passive movement of particles from a region of high concentration to a region of low concentration (down a concentration gradient)

10. 2.4.5 Passive transport: 2. Facilitated diffusion
Passive movement of particles from a region of high concentration to a region of low concentration (down a concentration gradient), through a selectively permeable membrane, facilitated by carrier proteins
Carrier proteins are integral proteins that allow some molecules to pass through

11. Solute = component of solution
Solvent = substance that dissolves the solute

12. 2.4.4 Passive transport: 3. Osmosis
Passive movement of water molecules from a region of low solute concentration (high water concentration) to high solute concentration (low water concentration) through a selectively permeable membrane

15. 2.3.6 Active transport
Uses energy, in the form of ATP, to move molecules against a concentration gradient, using membrane protein pumps
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16. 2.3.6 Active transport
E.g sodium potassium pump –action potential produced by nerve cells.

17. How do cells take in large particles that cannot be diffused?

19. 2.4.7 Vesicles

20. Membrane fluidity
Unsaturated hydrocarbon tail of phospholipids have kinks that keep the molecules from packing together, enhancing membrane fluidity.
Cholesterol reduces membrane fluidity by reducing phospholipid movement at moderate temperatures but it also hinders solidification at low temperatures.

21. Liposomes for drug delivery
Artificially produced vesicles that can be used for transport of drugs around the body
Good method of targeting cancer