module 2 lectures 1+2

Question 1

function of lipids

Answer 1

Structural functions
– Membrane components
– Protein modification

Metabolic functions
– Energy storage

Other functions
– Cellular signalling, including hormones
– Enzyme cofators
– Electron carriers
– Pigments

Question 2

effects of chain length

Answer 2

longer chain length = increase melting point, decreased solubility in H20

Question 3

effect of double bonds

Answer 3

decrease melting point (the more the worse)

Question 4

Glycerophospholipids

Answer 4

fatty acids (often unsaturated) - glycerol - phosphate - alcohol (head group)

Question 5

Glycerophospholipid head groups

Answer 5

serine
glycerol
inositol
choline
ethanolamine

(SG ICE)

Question 6

Sphingolipids

Answer 6

Major membrane components

Derivatives of the amino alcohol sphingosine

N-acyl fatty-acyl derivatives of sphingosine are called ceramides

Question 7

Steroids

Answer 7

cholesterol is main one - important in membranes

Question 8

Lipid aggregates

Answer 8

Micelle
Bilayer
Vesicle

Question 9

Stabilisation of bilayers

Answer 9

Ionic bonds between head groups and
hydrogen bonds with water

van der Waals interactions between fatty acid tails

Question 10

Lipid mobility in phospholipid bilayers

Answer 10

Lipids have two main types of motion:
* Spinning without changing location
– Rotation around their long axis
* Lateral diffusion – movement with the
same leaflet (VERY FAST!)

viscosity like olive oil

they could possible flip flop but it requires a lot of energy and uncatalysed it takes a loooong time t1/2

Question 11

FRAP experiments

Answer 11

show lateral diffusion

Fluorescence recovery after photobleaching: shows that lipids can easily move laterally in a lipid bilayer

Question 12

effect of heat on membranes

Answer 12

disorders them and change them from gel to fluid

Question 13

effect of lipids on bilayers

Answer 13

• Long chain fatty acids aggregate extensively to give low fluidity (gel-like
  state)
• Short chain fatty acids have less surface area to aggregate and increase fluidity
• Unsaturated fatty acids also aggregate less extensively and increase fluidity

Question 14

effects of sphingomyelin and cholesterol on membrane

Answer 14

Sphingomyelin (SM) associates into a thicker, more gel-like bilayer than phospholipids

Cholesterol increases thickness by ordering fatty acid tails, and stabilises head group interactions

Question 15

Leaflet composition

Answer 15

Exoplasmic leaflet – rich in sphingolipids + PC (less fluid)

Cytosolic leaflet – rich in PE/PS/PI (more
fluid)

Cholesterol is relatively evenly distributed in both leaflets

Question 16

How does asymmetry arise in leaflets?

Answer 16

Specific enzymes can catalyse
translocations

e.g. Sphingomyelin is synthesised in the exoplasmic face of the Golgi which becomes the exoplasmic face of the plasma membrane
– Glycerophospholipids are synthesised on the cytosolic face of the ER which becomes the cytosolic face of the plasma membrane
– PC arrives at the plasma membrane on the cytosolic side but is transported to the other leaflet by “flippase” enzymes which require energy from ATP hydrolysis.

Question 17

Flippase

Answer 17

flip-flops/ moves phospholipids from outer leaflet to inner

Question 18

Floppose

Answer 18

flip-flops/ moves phospholipids from inner leaflet to outer

Question 19

Scramblase

Answer 19

moves phospholipids either direction toward equilibrium (flip/flop)

Question 20

lipid rafts

Answer 20

Stable associations of sphingolipids and cholesterol

Can be disrupted by methyl-3-b-cyclodextrin (removes cholesterol from membranes) or the antibiotic filipin (sequesters cholesterol)

Question 21

Types of membrane proteins

Answer 21

Integral (= transmembrane, intrinsic)
– Firmly associated with the membrane
(need detergents to release)
– Span membrane
hydrophobic and hydrophilic surfaces

Lipid-anchored
– Protein covalently linked to one or more lipid molecules
– The lipid is embedded in a membrane leaflet to anchor the protein
– The polypeptide does not enter the bilayer (released using phosholipase C)

Peripheral (= extrinsic)
(released with milder treatment)
* Carbonate at high pH; Ca2+-chelating agent; high salt
– Does not contact the hydrophobic core of the bilayer
– Forms hydrophilic interactions with membrane surface or other membrane
proteins