membranes and lipids

Question 1

the selective permeability of the membrane

Answer 1

hydrophobic interior- restricts movement of ions+ biomolecules.

Question 2

Ion concentration variations within the cell and the extracellular environment

Answer 2

• [K+] high inside the cell, low outside
• [Na+]low outside, high outside
• [H+] gradient in mitochondria

Question 3

the 3 principal lipid components in the bilayer

Answer 3

1) phosphoglycerates- these are phospholipids
2) sphingolipids- mostly glycolipids (contain carbohydrates)
3) cholesterol- a sterol

Question 4

phosphoglycerates

Answer 4

polar head group (phosphate and alcohol). hydrophobic tails (2 FAs esterified to glycerol backbone). by convention, phosphate is attached to C3

Question 5

sphingolipids

Answer 5

contain a sphingosine moiety, which includes a fatty acid chain. Have 2 hydrophobic tails; one is the tail of sphingosine, the other a fatty acid residue. common in neuronal membranes, eg. sphingomyelin in neurons

Question 6

sterols

Answer 6

lipophilic compounds characterised by 4 fused hydrocarbon rings

Question 7

the sterol cholesterol

Answer 7

structurally more rigid than other membrane lipids. comprises >10% of total lipid in plasma membrane and golgi. cholesterol helps to maintain membrane fluidity (by sitting in pockets formed by cis-conformation fatty acids)

Question 8

integral membrane proteins

Answer 8

contain transmembrane domains, and can have hydrophilic domains protruding into the extracellular and/or cytoplasmic spaces

Question 9

peripheral membrane proteins

Answer 9

associated with the lipid bilayer, but generally separate with the aqueous component in cellular fractionation

Question 10

lipid-anchored proteins

Answer 10

bound to either the inner or outer membrane surface eg, proteins with a GPI anchor

Question 11

membrane protein function

Answer 11

1) transporters [require energy] and channels [do not]
2) enzymes
3) receptors
4) cell-cell recognition
5) intercellular joining
6) attachment to cytoskeleton and extracellular matrix

Question 12

the glycocalyx

Answer 12

• consists of the oligosaccharides on surface proteins and lipids extend into aqueous medium
• the outer leaflet contains a high proportion of phosphatidylcholine and sphingomyelin
• inner leaflet contains phosphatidylserine and phosphatidyl-ethanolamine
• phosphatidylserine is negatively charged, so may promote binding of positive charges inside the membrane.

Question 13

flippase

Answer 13

selectively moves lipids to the cytoplasmic side of the membrane

Question 14

floppase

Answer 14

selectively moves lipids towards the extracellular direction

Question 15

scramblase

Answer 15

moves lipids in either direction, promoting equilibrium