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Lipid Metabolism Flashcards

Lipid Metabolism

Matching

  • Chylomicrons: Lipoproteins formed in intestinal mucosal cells.
  • HDL (High-Density Lipoprotein): Transports cholesterol and other lipids from tissues to the liver.
  • Dihydroxyacetone Phosphate: Catabolized product of the glycerol backbone of triacylglycerols.
  • Albumin: Free fatty acids bind to albumin for circulation in the bloodstream.
  • LDL (Low-Density Lipoprotein): Cells take up LDL via receptor-mediated endocytosis.
  • Propionyl-CoA: The final product of β-oxidation of odd-numbered fatty acids.
  • Ketone Bodies: Acetoacetate, acetone, and D-β-hydroxybutyrate are metabolic fuels termed ketone bodies.
  • Phosphopantetheine: A prosthetic group contained in Acyl Carrier Protein (ACP).
  • Malonyl-CoA: Required along with acetyl-CoA for fatty acid synthesis as initiator molecules.
  • Cholesterol: Formed from the ordered condensation of isoprene units.

Multiple Choice

  • Bile acids aid in the digestion of triacylglycerols, synthesized by the liver from cholesterol derivatives.
  • High levels of cholesterol synthesis result in a net increase in uptake of LDL by the liver.
  • Entry of fatty acids into the oxidation pathway requires:
    • Priming via the enzyme acyl CoA synthetase.
    • Conservation of free energy from ATP hydrolysis by use of a thioester linkage.
  • Vitamin B12 is part of the prosthetic group 5¢-deoxyadenosylcobalamin.
  • Ketosis: A condition where acetoacetate production exceeds its metabolism, leading to sweet breath odor due to the decarboxylation of acetoacetate to acetone.
  • Glyceroneogenesis: Triacylglycerols are synthesized during starvation via a process known as glyceroneogenesis, utilizing Dihydroxyacetone phosphate.
  • Cardiolipin: Formed when two phosphatidylglycerol molecules condense, eliminating glycerol as a side product.
  • Interfacial Activation: Controls lipase activity at the lipid-water interface.
  • Lipoprotein Density Ranking: HDL > LDL > IDL > VLDL > chylomicrons (from highest to lowest density).
  • Apolipoproteins: (with the possible exception of apoB-100):
    • Are water-soluble and loosely associate with the lipoproteins.
    • Contain helices with hydrophobic and hydrophilic groups on opposite sides of the helical cylinder.
    • Appear to float on the surface of phospholipids.
  • Knoop’s Experiments: Involved the novel use of chemical labels to elucidate metabolic mechanisms demonstrating that fatty acids are broken down by two carbons at a time.
  • Peroxisomes:
    • β-oxidation in peroxisomes can shorten very long fatty acids.
    • Mammalian peroxisomes can synthesize some lipids, including bile salts.
    • In plants, peroxisomes and glyoxysomes serve as the site of β-oxidation.
    • Long chain fatty acids are transported into the peroxisome via a carnitine carrier protein where they are activated for oxidation.
    • β oxidation in peroxisomes varies slightly from the mitochondrial process.
  • Sphingomyelin: An important structural lipid found in nerve cell membranes and is a type of phospholipid.
  • Prostaglandins: Trigger pain and inflammation, synthesized by an enzyme inhibited by aspirin.
  • Cholesterol: A precursor to steroid hormones such as androgens and bile acids.
  • Arachidonic Acid: A 20-carbon fatty acid used for the synthesis of prostaglandins.
  • Sphingosine Synthesis: Requires palmitoyl-CoA and serine.
  • HMG-CoA to Acetoacetate Conversion: Occurs in the mitochondria of liver cells, producing acetoacetate + Acetyl-CoA.
  • HMG-CoA Reduction to Mevalonate: Takes place in the cytosol of liver cells, requiring 2 NADPH, producing mevalonate + 2 NADP+ + Acetyl-CoA.
  • HMG-CoA Reductase: Catalyzes the key regulatory step of cholesterol synthesis.
  • Sphinganine: An intermediate in the synthesis of ceramides, sphingomyelins, and cerebrosides.
  • Acetyl-CoA Carboxylase:
    • Produces malonyl CoA.
    • Uses acetyl CoA.
  • ATP Production: Net ATP production from complete catabolism of a fatty acid to CO2 and H2O falls in the range of 51-90.
  • Phosphatidic Acid Reactions: The reaction of two or more phosphatidic acids with two or more glycerol-3-phosphates could produce phosphatidylglycerol and cardiolipin.
  • Condensing Enzyme (KS) Mechanism: Covalent catalysis using a cys residue in the active site.
  • Fatty Acid Synthesis:
    • Occurs in the cytosol.
    • In eukaryotes, the process occurs on a single large protein.
    • The growing acyl chain is carried on an acyl carrier protein instead of coenzyme A.
    • The process requires two NADPH per acetyl group (2 carbons) added.
  • Ketone Body Formation: Promoted by a diet high in fat, high in protein, and low in carbohydrates.
  • Phospholipid Synthesis: Addition of polar “head groups” to diacylglycerol usually involves CDP derivatives.
  • HMG CoA Reductase Inhibition: Inhibited by the statin group of drugs (e.g. Lipitor®).
  • Malonyl CoA: The source of two-carbon fragments in fatty acids biosynthesis.
  • Acetyl CoA: The starting metabolite in ketone body biosynthesis.
  • HMG-CoA Reductase:
    • Highly regulated.
    • The active site is tightly bound by statins.
    • HMG-CoA reductase levels are decreased as a result of high cholesterol concentrations in the ER.
    • HMG-CoA reductase levels are decreased by the same factor that down regulated production of the LDL receptors.
  • Acyl-CoA Dehydrogenase Product: Results in the formation of a double bond between α and β carbons.
  • Aspirin Mechanism: Acts by acetylating a serine residue, preventing adequate enzyme activity.
  • PGH2: Synthesized from arachidonate and triggers pain and inflammation.
  • Tricarboxylate Transport System: Citrate synthase, ATP citrate lyase, malate dehydrogenase, and malic enzyme are all involved in the transport of acetyl-CoA into the cytosol.
  • Acetoacetate Formation: Formed by the condensation of acetyl CoA and acetyl-CoA.
  • Cholesterol Synthesis Sequence: Dimethylallyl pyrophosphate > geranyl pyrophosphate > farnesyl pyrophosphate > squalene.
  • Lanosterol: Produced by the multistep cyclization of squalene.
  • Unsaturated Fatty Acid Breakdown Problems: β, γ double bond, unanticipated isomerization, and inhibition of hydratase by a double bond.
  • LDL Uptake by Liver: Taken up by the ER and used to control synthesis of HMG CoA reductase and LDL receptor synthesis.