M&R 1.2 - Membrane Proteins, Membrane Asymmetry and the Cytoskeleton Flashcards
What are the functions of membrane proteins?
- Facilitated diffusion
- Maintain ion gradients
- Specificity (responses)
(Functional evidence)
What are the biochemical evidences for membrane proteins?
- Membrane fractionation and gel electrophoresis
- Freeze Fracture
How can proteins be mobile in bilayers? (4)
- Conformational changes
- Rotation
- Lateral Diffusion
- NO FLIP FLOP DUE TO LARGE HYDROPHILIC MOIETIES
How is the mobility of proteins restricted in the membrane? (4)
- Aggregates of proteins form together which decreases movement
- Tethering
- Interactions with other cells (stick together)
- Lipid mediated effects
What is tethering?
Membrane proteins hold on to the basement membrane
What is meant by lipid mediated effects?
Membrane proteins separate into cholesterol poor regions/ fluid phase
Where can membrane proteins be located in the membrane?
- Peripheral
- Integral
Describe peripheral membrane proteins (3)
- Surface bound by ionic or hydrogen bonds
- Associated, not integral
- Removed from bilayer by a change in pH or ionic strength
Describe integral membrane proteins (2)
- Interact with hydrophobic areas
- Have to be removed by aggressive means e.g. Detergents/ organic solvents as they compete for non-polar interactions.
How are membrane proteins inserted into the bilayer?
- Secretory pathway
- Stop transfer signal reached
- Protein is translated in cytoplasm and leaves stop transfer signal in endoplasmic reticulum therefore spanning the membrane
Describe the stop transfer signal
18-22 highly hydrophobic amino acids
Describe the amino acids that make up transmembrane proteins (4)
SHUP
- Small
- Hydrophobic
- Uncharged
- Polar
What happens if there are no signal peptidase sites?
- No cleavage
- N-terminal remains outside
- C-terminal remains inside
What is topology?
- N-terminal = in cytoplasm
- C-terminal = outside cell
What is the cytoskeleton?
A cage structure grafted on to the inside of the plasma membrane
