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Once acyl chains are synthesized, they can be added to backbone molecules (which two
Acyl chains can be added to sphingosine and glycerol backbones.
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.
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.
glycerolphospholipids, sphingolipids, and cholesterol, steroids and isoprenoids.
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
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…
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.
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.
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.