W4 - Membrane Proteins

Question 1

What is the function of bacteriorhodopsin?

Answer 1

Creates proton gradients required for ATP formation

Question 1

Bacteriorhodopsin is a spanning membrane protein and has 7TM alpha helices, what type of aa are alpha helices predominantly made up of?

Answer 1

Hydrophobic aas

Question 2

Porins have beta sheets, where are the hydrophobic/philic aas found?

Answer 2

Phobic - contact with membrane, philic - inside the barrel (they tend to alternate due to one being above/below plane)

Question 3

Prostaglandin H2 synthase-1 is a peripheral membrane protein, what does it do?

Answer 3

Catalyses first step of prostaglandin synthesis

Question 4

What do prostaglandins do?

Answer 4

Increase/promote inflammation and can alter gastric acid secretion

Question 5

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?

Answer 5

Aspirin

Question 6

Parts of the protein that interact with hydrophobic parts of the membrane have polar/non-polar side chains

Answer 6

Non-polar

Question 7

What can form accurate predictions of TM alpha helices?

Answer 7

The aa sequence (beta cannot be predicted)

Question 8

How many residues are required to span the hydrophobic core of the membrane (about 30A)?

Answer 8

20

Question 9

What does a hydropathy plot calculate?

Answer 9

Hydrophobicity index

Question 10

Free energy of transfer can measure what and what does it mean if this is -ve or +ve?

Answer 10

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)

Question 11

What is a criterion level of the hydropathy index to show where the start of the alpha helix in the membrane is?

Answer 11

+84 kJ/mol

Question 12

What happens during FRAP?

Answer 12

Cell is observed under fluorescence, very fine beam bleaches cell/membrane, observe restoration of colour (rate of diffusion)

Question 13

If temperature is lowered during FRAP what would happen differently?

Answer 13

The bleach will stay

Question 14

What is the equation used in FRAP experiments to measure the average distance traversed in a set set?

Answer 14

S = (4Dt)^1/2

Question 15

Give examples of membrane proteins that laterally diffuse slowly and quickly

Answer 15

Rhodopsin - very mobile (0.4micro per sec), fibronectin - very low mobility (10^-4micro per sec)

Question 16

What can affect the rate of lateral diffusion of membrane proteins?

Answer 16

THe amount of proteins/how crowded the membrane is

Question 17

Which is faster, lateral or transversal diffusion of lipids?

Answer 17

Lateral

Question 18

Transversal diffusion of lipids is very rare, what does this therefore maintain for long periods?

Answer 18

Membrane asymmetry

Question 19

Do proteins every undergo transversal diffusion?

Answer 19

No

Question 20

What does a C=C (cis) bond do the the temperature required to cause a membrane to go from solid-like and fluid-like?

Answer 20

It lowers the temp required (due to lowering packing density of membrane)

Question 21

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?

Answer 21

Cholesterol

Question 22

Why do membrane proteins create asymmetry of the membrane?

Answer 22

They are inserted at a specific orientation and do not rotate

Question 23

Peroxisomes and mitochondria in eukaryotes have 1 and 2 membranes respectively, what are each of their functions?

Answer 23

P - oxidation of FAs for energy conservation, M - ATP generation