Membrane Structure

Question 1

membrane components

Answer 1

lipid bilayes that are ~5nm think, proteins in membrane mediate most of the functions (~30% of genome is membrane proteins), contains cholesterol, is dynamic

Question 2

membrane fluidity

Answer 2

degree of motion possible among phospholipids in a bilayer. Cholesterol makes membrane less fuild, unsaturated acyl chains make it more fluid. Some lipids are anchored and some are free floating (affects degree of fluidity) Curvature depends on size of polar head groups on membrane.

Question 3

phosphoglycerides

Answer 3

glyucerol-3-phosphate backcone with 2 fatty acyl chains at one end (varying degrees of saturation), and a polar head group at the other (ethanolamine, inositol, etc.). Head group determines type

Question 4

Sphingolipids

Answer 4

sphingosine (acyl unit) and either of 2 polar head groups and an attached fatty acid chain

Question 5

Sphingomyelin

Answer 5

sphingolipid with phosphocholine head group. Made in the ER, finished in Golgi apparatus

Question 6

asymmetry of bilayers

Answer 6

some phospholipids don?t flip sides without enzyme activity. During apoptosis, lipids from inside move outside and attract macrophages to kill it. Size of lipid affects its curvature. Proteins can me go through membrane or be embedded in surface.

Question 7

integral proteins

Answer 7

fully or partially embedded. Can go multiple times through memnbrane back and forth

Question 8

Peripheral membrane proteins

Answer 8

covalently interacting with proteins bound in the membrane, but not embedded

Question 9

complex that regulates cholesterol synthesis

Answer 9

SREBP-SCAP complex and Insig -1 and 2

Question 10

SREBP

Answer 10

sterol regulatory element binding proteins contains bHLH transcription factor which activates cholesterol synthesis

Question 11

SCAP

Answer 11

SREBP cleavage activing protein - bound to SREBP. Contains sterol binding domain, cleaves SREBP

Question 12

presence of cholesterol

Answer 12

SREBP-SCAP complex is bound to Insigs and is retained in the ER

Question 13

absence of cholesterol

Answer 13

SREBP-SCAP complex dissociates from Insig and is transferred to the Golgi where SREBP undergoes 2 step proteolysis (RIP), releasing bHLH (latent transcription factor) to synthesize cholesterol and LDL-receptors

Question 14

HMGcoA reductase

Answer 14

first unique enzyme of cholesterol synthesis, target of statins