Membrane composition

Question 1

flippases

Answer 1

Move phospholipids from outer to inner leaflet of bilayer
Requires ATP
Highly specific

Question 2

floppases

Answer 2

Move phospholipids from inner to outer leaflet of bilayer
Requires ATP
Specific

Question 3

scramblases

Answer 3

Move phospholipids in both directions
No ATP needed
Non-specific

Question 4

factors affecting membrane fluidity

Answer 4

Temperature
Acyl chain length
Acyl chain saturation

Question 5

Effect of temperature on membrane fluidity

Answer 5

cold=rigid/less fluid
so at cold temperatures, an organism would have more unsaturated fatty acids

Question 6

effect of acyl chain length on membrane fluidity

Answer 6

shorter chains increase fluidity as they have fewer van der waals forces so are less tightly packed

Question 7

effect of acyl chain saturation on membrane fluidity

Answer 7

Unsaturated fatty acids form kinks so cant pack closely together so increase fluidity

Question 8

is the membrane symmetrical or asymmetrical

Answer 8

asymmetrical

Question 9

why do hydrophobic molecules clump together

Answer 9

reduce SA:V in contact with water

Question 10

lipid movement within membranes

Answer 10

Lateral diffusion
Flip-flop (not spontaneous)
Rotation
Flexion

Question 11

how is membrane fluidity measured

Answer 11

FRAAP (fluorescence recovery after photobleaching)
protein of interest is labelled with a fluorescent marker, and the fluorescence in a small patch of membrane is then irreversibly “bleached” by a pulse of light from a focused laser. The time it takes for fluorescence to return to the bleached membrane patch provides a measure of how rapidly unbleached, fluorescently labelled proteins diffuse through the bilayer into the area. This “recovery” is plotted on a curve that shows fluorescence over time.

Question 12

noncytosolic monolayer

Answer 12

phosphatidylcholine
sphingomyelin
Glycolipids
cholesterol (= to cytolsolic)

Question 13

cytosolic monolayer

Answer 13

phosphatidylserine
phosphatidylethanolamine
phosphatidylinositols
cholesterol (= to non cytosolic)

Question 14

types of membrane protein

Answer 14

Integral
Peripheral
Lipid-anchored

Question 15

Peripheral membrane proteins

Answer 15

Bind to surface by electrostatic interactions with the heads of lipids or other proteins

Question 16

Lipid-linked membrane protein

Answer 16

lipid covalently attached to protein

Question 17

nonpolar aliphatic R groups

Answer 17

glycine
alanine
valine
leucine
methionine
isoleucine

Question 18

aromatic R groups

Answer 18

phenylalanine
tyrosine
tryptophan

Question 19

polar, uncharged R groups

Answer 19

serine
threonine
cysteine
proline
asparagine
glutamine

Question 20

charged R groups (5)

Answer 20

lysine
arginine
histidine
aspartate
glutamate

Question 21

The polar nature of peptide bonds are not energetically favourable in the hydrophobic core of the lipid bilayer. How is this problem overcome

Answer 21

Hydrogen bonding between the partial negative charge in the carbonyl oxygen and the partial positive charge of the amide hydrogen in a regular pattern
Neutralises charges
Length of chain compressed due to the hydrogen bonding- alpha helix formation
This involves the backbone-not side groups

Question 22

beta barrel integral membrane protein

Answer 22

all carbonyl oxygens and amide hydrogens are also bonded in a regular pattern, but the hydrogen bonding patterns are further away. Tend to be found in mitochondrial outer membrane and bacterial outer membranes.

Question 23

helical bundle membrane proteins

Answer 23

the integral proteins that form alpha helices in the membrane

Question 24

antiparallel beta sheet

Answer 24

is formed with adjacent -strands running in opposite directions. Every other side chain extends above or below the sheet
Hydrogen bonding between strands

Question 25

dimensions of lipid bilayer

Answer 25

50 angstroms 30 of which are the hydrophobic region

Question 26

extended conformation, 1 residue=

Answer 26

3.5 angstrom

Question 27

alpha helical conformation, 1 residue=

Answer 27

1.5 angstrom 20 residues to span hydrophobic core

Question 28

hydrophobicity scale

Answer 28

negative=hydrophobic amino acid Average hydrophobicity of a stretch of amino acids is calculated, plotted on graph When window is over a hydrophobic stretch of amino acids there is a trough troughs indicate transmembrane regions Hydrophobicity analysis does not predict beta-barrel membrane proteins.

Question 29

how to remove integral membrane proteins from the lipid bilayer

Answer 29

detergents

Question 30

how to remove peripheral membrane proteins that are attached to protein

Answer 30

high salt concentrations

Question 31

protein channels structure-multipass transmembrane proteins

Answer 31

series of alpha helices that cross bilayer multiple times hydrophilic side chains form an aqueous pore