Lipids 4

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Lipids 4
2011-08-28 23:46:55

cholesterol metabolism
Show Answers:

  1. How many carbons are in cholesterol
  2. How many rings of cholesterol
  3. Does cholesterol have a side chain
    Yes, 8 carbons long
  4. What is the fuction of the hyrdoxyl on cholesterol
    This is the form of cholesterol in membranes

    Location for acylation
  5. What is the function of acylated cholesterol?
    Storage form of cholesterol (with fatty acid chain)

    Translocation of cholesterol in plasma lipoproteins
  6. Where is cholesterol made?
    Liver, cytosol, with HMG coA reductase associated with the cytosolic side of the ER
  7. Describe the conversion of acetyl co A to mevalonate
    Acetyl co A thiolase: add to acetyl co A, eliminate co Ash

    HMG co A synthase: add acetyl group withanother acetl co A, eliminate coAsh

    HMG co A reductase: eliminate acetyl co A and reduce C=O to form mevelonate. Uses 2 NADPH -->NADH
  8. Synthesis of cholesterol from mevolonate
    6 carbon mevolonate --> 5carbon isoprenePP (uses 3 ATP and eliminates a CO2)

    5 carbon isoprenePP X 3 =15 carbon farnesyl PPi

    15 carbon farnesyl PPi X2 = 30 C Squaline

    30 carbon squaline + OH plus cycle= Lanosterol

    30 carbon lanosterol minus 3 CH3, reduce double bond, shift bond = 27 carbon cholesterol
  9. Regulation of HMG CoA reductase
    • Increased activity by:
    • dephos of enzyme by insulin

    • Decreased by:
    • phos of enzyme by glucagon
    • high concentration of cholesterol
    • inhibited by statins
  10. What are bile salts
    Modified cholesterol to make more soluble in water, and to prevent aggregation of cholesterol
  11. Name 3 differences between cholesterol and cholate
    • Cholate has:
    • 5 carbon side chain instead of 8 C
    • COO on side chain
    • Hydroxylated on C7, C12
    • Fully saturated rings
  12. Role of glycine and taurine
    Amino groups added to side chain by amino bond. Makes more soluble in water
  13. Where are bile acids produced? Stored? Reabsorbed?
    • Produced: liver cytosol
    • Stored: gallbladder
    • Reabsorbed: ilium and returned via hepatic portal vein
  14. Cholelithiasis
    • Deficiency of bile acid production
    • Gallstones
  15. Steatorrhea
    Fatty feces from inability to produce enough bile to break down fat
  16. Steriods
    Derived from cholesterol

    have shortened side chain (usually about 27 carbons)

    addition on carbonyl and hydroxyl groups, double bonds
  17. Vitamin D
    Formed from modified cholesterol by UV radiation (photolysis)
  18. cholecalceferol
    vitamin D
  19. calcitriol
    activated vidamin d (in liver/kidney)