The carbon chain of fatty acids is shortened by 2 carbon atoms at a time. This involves successive reactions catalyzed by 4 enzymes. These act in the following order: Acetyl CoA de... The carbon chain of fatty acids is shortened by 2 carbon atoms at a time. This involves successive reactions catalyzed by 4 enzymes. These act in the following order: Acetyl CoA dehydrogenase, enoyl hydratase, D-OH acyl CoA dehydrogenase, thiolase. Substrate level phosphorylation in TCA cycle is in step: Isocitrate dehydrogenase, Malate dehydrogenase, Aconitase, Succinate thiokinase. One molecule of glucose gives how many molecules of CO2 in TCA cycle? In TCA cycle, succinate is converted to ketoglutarate by the enzyme: Fumarase, Isocitrate dehydrogenase, Aconitase, Succinate. The initial step of the citric acid cycle is: Conversion of pyruvate to acetyl-CoA, Condensation of acetyl-CoA with oxaloacetate, Conversion of citrate to isocitrate, Formation of α-ketoglutarate catalyzed by isocitrate dehydrogenase.

Understand the Problem
The question is asking about metabolic processes related to fatty acids and the TCA cycle, highlighting the enzymes involved and the number of CO2 molecules produced from glucose. It is focused on biochemical pathways and enzyme functions.
Answer
66: A, 67: D, 68: A, 69: Error, 70: B
66: A - The correct sequence of enzymes is Acetyl CoA dehydrogenase, enoyl hydratase, D-OH acyl CoA dehydrogenase, thiolase. 67: D - Substrate level phosphorylation in the TCA cycle is catalyzed by succinate thiokinase. 68: A - One molecule of glucose yields 6 molecules of CO2 in the TCA cycle. 69: There is an error. Succinate is converted to fumarate by succinate dehydrogenase. 70: B - The initial step of the TCA cycle is the condensation of acetyl-CoA with oxaloacetate.
Answer for screen readers
66: A - The correct sequence of enzymes is Acetyl CoA dehydrogenase, enoyl hydratase, D-OH acyl CoA dehydrogenase, thiolase. 67: D - Substrate level phosphorylation in the TCA cycle is catalyzed by succinate thiokinase. 68: A - One molecule of glucose yields 6 molecules of CO2 in the TCA cycle. 69: There is an error. Succinate is converted to fumarate by succinate dehydrogenase. 70: B - The initial step of the TCA cycle is the condensation of acetyl-CoA with oxaloacetate.
More Information
The TCA cycle yields 6 CO2 per glucose because each pyruvate yields 3 CO2, and glucose splits into 2 pyruvate. The conversion error in question 69 stems from incorrect enzyme pairing—succinate dehydrogenase converts succinate to fumarate, not α-ketoglutarate. The initial TCA cycling begins with the condensation of acetyl-CoA with oxaloacetate, crucial for citrate formation.
Tips
Check the specific enzyme roles in metabolic pathways to avoid pairing errors. Misidentifying catalytic processes leads to logical errors, especially in enzyme functions.
Sources
- Oxidation of Fatty Acids - Chemistry LibreTexts - chem.libretexts.org
- Biochemistry, Fatty Acid Oxidation - StatPearls - NCBI Bookshelf - ncbi.nlm.nih.gov
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