Flashcards in Membrane Structure Deck (18)
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1
What are the molecular components of the membrane?
lipids (lipid bilayer)
carbohydrates (usually on extracellular domains of lipids or proteins)
proteins (30% of encoded proteins are membrane-associated
2
Explain the concept of membrane fluidity
phospholipids diffuse rapidly (10^7times/sec)
- several mm/s @ 37C
- do not spontaneously flip-flop (need ATP driven flipase)
3
What are the parts of a phospholipid?
Diglyceride
Phosphate group
Choline
4
What are the parts of a sphingolipid?
long
charged
have amine
- may have sugar
5
What are the parts of a cholesterol?
Polar hydroxyl group
Rigid steroid ring group
Hydrocarbon tail
6
How are membrane bilayers asymmetric?
carbohydrates on extracellular side
- non-uniform distribution of lipids/ proteins
more - phosphipids (PS, PE, PI) on inside of membrane
PC, sphingomyelin, glycolipids on outside
7
What are the different ways proteins can associate with membranes?
Transmembrane (x 1, x>1, cylinder)
Intra/extracellular (self-anchored, lipid anchored, oligosaccaride linked, monocovalent interaction with another protein)
8
How is cholesterol synthesis regulated?
SYNTHESIS
~30 enzymes
Statins: blick first step- HMGCoAreductase
UPTAKE
-negative feedback loop
-depends on LDLR
-enough through diet -> decrease synthesis
BOTH
- SREBP: regs LDLR and all synth enzymes
9
What is the function of proteins in the membrane?
Control the movement of molecules between the inside and outside of the cell
10
What does membrane fluidity depend on?
composition and temperature
11
What are the characteristics of phospholipids? Examples?
amphipathic (hydrophilic & hydrophobic)
Phosophatidylethanolamine (PE)
Phosphastidylcholine (PC)
Phosphatidylserine (PS)
Phosphatidyllinositol (PI)
- derived from glycerol
12
How do cholesterols interact with other lipids?
interaction of ring and other lipids's tails immobilize - decreases fluidity
tails are straightened by cholesterol - > membrane thickness
13
Where does cholesterol come from?
ingestion/ uptake
synthesis by the liver
14
What is SCAP?
SREBP cleavage activating protein
15
What is Insig
cholesterol regulating protein
16
What happens when cholesterol is high?
Insig binds SCAP-> blocks signaling
17
What happens when cholesterol is low?
SCAP binds SREBP -> goes to golgi -> bHLH released from SREBPby RIP (regulated intramembrane proteolysis) ->cleaved by S1P & S2P-> bHLH moves into nucleus -> binds promoters, activates genes to produce LDLRs & increase enzymes involved in cellular synthesis of cholesterol
18
