Cells & Membranes

1. Cells & Membranes

2. Prokaryotic vs. Eukaryotic Cells • Why would a cell have organelles? • Different “compartments” for specific reactions • Allows incompatible reactions to occur at the same time

3. Protein Traffic in a Cell • Secretory Protein = protein that is going to leave the cell • Pathway: • Ribosome  Rough ER  vesicle  Golgi Apparatus  vesicle  Plasma (Cell) Membrane

4. Movement within a cell • Involves specialized proteins “walking” across microtubules or other proteins • Requires ATP as an energy source • Examples include: • Vesicle movement within a cell • Cilia and flagella movement • Muscle contraction

5. Membrane Properties • fluid = phospholipids move a lot laterally but not much flip-flopping • Membranes need to stay fluid to function properly. Fluidity of the membrane can be adjusted by • Temperature • Amount of cholesterol

6. Fluidity of the membrane • Effect of temperature • the higher the temperature, the more fluid the membrane will be • At a certain temperature, each membrane will become more solidified (less fluid) • This depends on the types of fatty acids in the membrane (saturated or unsaturated)

7. Fluidity of the membrane • Effect of cholesterol • At medium temperatures - reduces fluidity - prevents lateral movement of phospholipids • At low temperatures • prevents solidification -- lowers the temperature at which a membrane solidifies • Prevents phospholipids from being packed closely

8. Membrane Properties • Mosaic = proteins, carbohydrates embedded in membrane • Integral/Transmembrane proteins often have both hydrophilic and hydrophobic regions. • Membrane proteins have many different functions. • Carbohydrates are often involved in cell-cell recognition.

9. Why must a plasma membrane be selectively permeable? • To control what enters the cell • Maintain a certain environment within the cell

10. Passive Transport • Require NO energy • Moves with the concentration gradient • From high to low concentrations • Osmosis • Diffusion of water

11. Passive Transport • Facilitated Diffusion • Channel Proteins • Carrier Proteins • What would you expect the amino acid composition to be on the channel portion of the protein? • hydrophilic (so that hydrophilic molecules can get across)

12. Active Transport • Requires energy • Moves against the gradient • From low to high concentrations • Endocytosis • Cell “eating”– taking molecules in • Exocytosis • Expelling molecules from a cell