Flashcards in Membrane Structure Deck (18)
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
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)
What are the parts of a phospholipid?
What are the parts of a sphingolipid?
- may have sugar
What are the parts of a cholesterol?
Polar hydroxyl group
Rigid steroid ring group
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
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)
How is cholesterol synthesis regulated?
Statins: blick first step- HMGCoAreductase
-negative feedback loop
-depends on LDLR
-enough through diet -> decrease synthesis
- SREBP: regs LDLR and all synth enzymes
What is the function of proteins in the membrane?
Control the movement of molecules between the inside and outside of the cell
What does membrane fluidity depend on?
composition and temperature
What are the characteristics of phospholipids? Examples?
amphipathic (hydrophilic & hydrophobic)
- derived from glycerol
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
Where does cholesterol come from?
synthesis by the liver
What is SCAP?
SREBP cleavage activating protein
What is Insig
cholesterol regulating protein
What happens when cholesterol is high?
Insig binds SCAP-> blocks signaling
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