Chapter 19-4

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Chapter 19-4
2014-04-27 23:00:53
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  1. Once acyl chains are synthesized, they can be added to backbone molecules (which two
    backbone molecules?):
    Acyl chains can be added to sphingosine and glycerol backbones.
  2. What are the common precursors of triacylglycerols, sphingolipids and glycerophospoholipids?:
    • Fatty acyl-CoA, from acyl-CoA synthase or “activation in beta-oxidation” AND acetyl-CoA (for cholesterol).
    • Glycerol 3-phosphate from glycolysis (reduction of DHAP) or glycerol phosphorylation.
  3. Note the energy and reducing equivalent expenditure necessary to produce phosphatidic acid (what are its functions?):
    • NADH + H+ + 3ATP + 2 CoA-SH à NAD+ + ADP + 2AMP + 2PPi + 2CoA-SH.
    • Phosphatidic acid functions as key intermediates in the formation of triacylglycerols and glycerolphospholipids.
  4. Membrane lipids:
    glycerolphospholipids, sphingolipids, and cholesterol, steroids and isoprenoids.
  5. Strategies for adding polar head groups to acyl chains (in this case, archindonate (diacylglycerol)) (Skeleton):
    • Note:diacylglycerol + phosphate + head group = glycerophospholipids.
    • (1) “activate” 1.2-diacylglycerol via CTP
    • (2) “activated” the polar head group via CTP
    • (3) Head group exchange via one of the many salvage pathways
  6. Strategies for adding polar head groups to acyl chains (in this case, archindonate (diacylglycerol)) (Detail):
    • Strategies 1 and 2: makes phosphatidyl- serine/choline/ethanolamine (all one word names). Add (1) ADP to the head group or (2) diacylglycerol. Nucleophilic attack displaces CMP, leaves phosphoryl group, and subsequent simple reactions produce end products.
    • Strategy 3: A salvage pathway but not THE salvage pathway. This occurs in mammalian cells where a free serine displaces ethanolamine. The product is phosphatidylserine. Methyl transferase reaction yields phosphatidylcholine.

    • But none of these
    • strategies makes sphingolipid…
  7. Sphingolipid synthesis:
    sphingolipids and glycerophospholipids share some mechanisms. Palmitoyl-CoA + serine condense à sphinganine (sphingosine backbone). Sphinganine + fatty acid (amide linkage) à N-acylsphinganine. Desaturation of the acyl chain yields N-acylsphingosine (ceramide – parent molecule). A head group is attached – produces a cerebroside or sphingomyelin.
  8. Still need strategy for the synthesis of cholesterol, steroids and isoprenoids…
    27 carbons, all can be from acetyl-CoA condensations. An essential molecule in cell membranes. Not essential in the diet, made from simple precursors. Isoprene is a key intermediate.
  9. What is the molecule that is the ultimate precursor (the simplest initial reactant) in cholesterol synthesis?:
    • The precursor for cholesterol synthesis is acetate.
    • NOTE: acetyl coenzyme A is the commonly utilized form of acetate.