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.