Questions and Answers
Which enzyme is responsible for the elongation of palmitate in microsomes?
What is the primary source of 2-carbon units during mitochondrial elongation of fatty acids?
What type of fatty acids do mammals lack the ability to introduce double bonds at specific positions?
Which of the following fatty acids can be synthesized from linoleic acid?
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Which compound is not metabolized and is primarily exhaled through the lungs?
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What process refers to the formation of ketone bodies?
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Which enzyme system is involved in the formation of unsaturated fatty acids?
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Which of the following statements about ketone bodies is true?
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Which enzyme is responsible for the conversion of β-hydroxy butyrate to acetoacetate?
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What is the primary precursor for ketone body synthesis?
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What is the fate of acetoacetate in the absence of enzymatic decarboxylation?
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During which condition does the production of ketone bodies become most significant?
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Which ketone body is predominantly used by the brain during prolonged starvation?
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What reaction is catalyzed by thiolase in ketogenesis?
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Which of the following tissues is unable to utilize ketone bodies?
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What is the max concentration of total ketone bodies in well-fed conditions?
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Study Notes
Synthesis of Long Chain Fatty Acids from Palmitate
- Fatty acid elongase in the microsomal enzyme system elongates palmitate using 2-carbon fragments from malonyl-CoA and reducing equivalents from NADPH.
- Mitochondrial elongation of fatty acids is less active, primarily elongating fatty acids with less than 16 carbons, mainly short and medium chain fatty acids, using acetyl-CoA.
- Fatty acyl CoA desaturase system in microsomes forms unsaturated fatty acids, requiring flavin-dependent cytochrome b5 reductase, NADH, and molecular oxygen.
- Oleic acid (from stearate) and palmitoleic acid (from palmitate) are synthesized as monounsaturated fatty acids.
- Mammals cannot introduce double bonds between the 10th carbon and the methyl terminal (ω) end, making linoleic and linolenic acids essential dietary components.
- Arachidonic acid can be synthesized from linoleic acid via desaturation and chain elongation, serving as a precursor for eicosanoids like prostaglandins and thromboxanes.
Metabolism of Ketone Bodies
- Ketone bodies (acetoacetate, β-hydroxybutyrate, and acetone) are water-soluble energy sources, with acetone exhaled and not metabolized.
- Ketogenesis occurs exclusively in the liver, within the mitochondrial matrix of hepatic cells, utilizing acetyl-CoA derived from fatty acid oxidation, pyruvate, or specific amino acids.
- Ketogenesis involves the condensation of two acetyl-CoA molecules to form acetoacetyl-CoA, followed by condensation with another acetyl-CoA to create β-HMG-CoA, regulated by HMG-CoA synthase.
- HMG-CoA is then cleaved into acetoacetate and acetyl-CoA by HMG-CoA lyase, while β-hydroxybutyrate is produced by reducing acetoacetate using β-hydroxybutyrate dehydrogenase.
- Acetoacetate can spontaneously decarboxylate into acetone, with blood ketone body concentrations not exceeding 0.2 mmol/L in well-fed conditions.
Utilization of Ketone Bodies
- Ketone bodies (acetoacetate and β-hydroxybutyrate) serve as significant energy sources for peripheral tissues, including skeletal muscle and cardiac muscle.
- Tissues such as erythrocytes, lacking mitochondria, cannot utilize ketone bodies.
- The production and utilization of ketone bodies increase significantly under conditions of low glucose availability, observed in starvation or diabetes mellitus.
- During prolonged starvation, ketone bodies become a primary fuel source for the brain and other central nervous system regions.
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Description
This quiz covers the synthesis of long-chain fatty acids from palmitate, focusing on the mechanisms of microsomal and mitochondrial elongation. It explores the roles of enzymes like fatty acid elongase and the importance of malonyl-CoA and NADPH in the elongation process. Test your understanding of these biochemical pathways and their significance.
