W4 - Membrane Proteins Flashcards
What is the function of bacteriorhodopsin?
Creates proton gradients required for ATP formation
Bacteriorhodopsin is a spanning membrane protein and has 7TM alpha helices, what type of aa are alpha helices predominantly made up of?
Hydrophobic aas
Porins have beta sheets, where are the hydrophobic/philic aas found?
Phobic - contact with membrane, philic - inside the barrel (they tend to alternate due to one being above/below plane)
Prostaglandin H2 synthase-1 is a peripheral membrane protein, what does it do?
Catalyses first step of prostaglandin synthesis
What do prostaglandins do?
Increase/promote inflammation and can alter gastric acid secretion
The PG H2 synthase-1 has to be associated with the membrane + has a -phobic channel for arachidonic acid, what can inhibit this/disable the enzyme?
Aspirin
Parts of the protein that interact with hydrophobic parts of the membrane have polar/non-polar side chains
Non-polar
What can form accurate predictions of TM alpha helices?
The aa sequence (beta cannot be predicted)
How many residues are required to span the hydrophobic core of the membrane (about 30A)?
20
What does a hydropathy plot calculate?
Hydrophobicity index
Free energy of transfer can measure what and what does it mean if this is -ve or +ve?
The hydrophobicity of an aa (-ve number = energy required to keep aa in hydrophobic core, the molecule is polar and +ve number = energy required to remove aa from a hydrophobic core, molecule is non-polar)
What is a criterion level of the hydropathy index to show where the start of the alpha helix in the membrane is?
+84 kJ/mol
What happens during FRAP?
Cell is observed under fluorescence, very fine beam bleaches cell/membrane, observe restoration of colour (rate of diffusion)
If temperature is lowered during FRAP what would happen differently?
The bleach will stay
What is the equation used in FRAP experiments to measure the average distance traversed in a set set?
S = (4Dt)^1/2
Give examples of membrane proteins that laterally diffuse slowly and quickly
Rhodopsin - very mobile (0.4micro per sec), fibronectin - very low mobility (10^-4micro per sec)
What can affect the rate of lateral diffusion of membrane proteins?
THe amount of proteins/how crowded the membrane is
Which is faster, lateral or transversal diffusion of lipids?
Lateral
Transversal diffusion of lipids is very rare, what does this therefore maintain for long periods?
Membrane asymmetry
Do proteins every undergo transversal diffusion?
No
What does a C=C (cis) bond do the the temperature required to cause a membrane to go from solid-like and fluid-like?
It lowers the temp required (due to lowering packing density of membrane)
Bacteria have enzymes that can adapt the no. sat/unsat bonds and chain length but what do animals use as a key regulator in rigidity?
Cholesterol
Why do membrane proteins create asymmetry of the membrane?
They are inserted at a specific orientation and do not rotate
Peroxisomes and mitochondria in eukaryotes have 1 and 2 membranes respectively, what are each of their functions?
P - oxidation of FAs for energy conservation, M - ATP generation
