Membrane Structure

Question 1

• Bilayer: Composed of? Thickness? Spanning protein %? Carbs on what side?
• Composition of phosphoglycerides?
• Composition of sphingolipids? Ex?
• Composition of cholesterol? Effect on thickness and fluidity?
• What increases fluidity?
• Assymetrical makeup of bilayer?
• Integral proteins: Embedded how? Transmembrane domain structure?
• Peripheral protein: Attached how?

Answer 1

• lipids, cholesterol, proteins; 5 nm; 30%; EC side
• glycerol + phosphate with 2 fatty acyl chains and variable head group
• Long acyl unit (sphingosine) + 1/2 polar heads + fatty acid chain; sphingomyelin
• hydoxylated sterol ring + fatty acid chain; increased thickness; decreased fluidity
• Unsaturated acyl chains
• EC = PC, SM, glycolipids; IC = PE, PS, PI
• fully or partially (could be one side or both); often a helices
• Covalently interacting with protein but not attached to membrane

Question 2

• Cholesterol Regulation:
• What it bound in ER membrane?
• Ways we get cholesterol? Type of loop?
• Rate limiting enzyme? What target this?
• How many enzymes regulate this?
• Steps? (5)

Answer 2

• Insig to SCAP to SCREBP to bHlH TF
• Diet and synthesis; negative feedback
• HMGCOa reductase; statins
• 30+
  1. ) Low cholesterol, SCAP-SCREBP diss. from Insig
  2. ) SCAP escorts SCREBP to golgi via vessicular transport
  3. ) bHLH TF is released by 2 proteolysis RIP’s (SIP1 and SIP 2)
  4. ) SIP1 is luminol and SIP2 is in membrane; need cleavage from both
  5. ) bHLH-SCRBP moves into nucleus; Increases LDLR to increase cholesterol and increase synthesis via 30+ enzymes