Difficulty: Easy
Correct Answer: They are all components or products of the citric acid (Krebs) cycle
Explanation:
Introduction / Context:The citric acid cycle is a central metabolic hub. CoA forms acetyl-CoA to enter the cycle, CO2 is released during decarboxylation steps, oxaloacetate is both the starting and ending four-carbon acceptor, and FADH2 is a reduced cofactor produced at succinate dehydrogenase (Complex II).
Given Data / Assumptions:
Concept / Approach:Relate each item to a specific TCA step to confirm their commonality with the Krebs cycle.
Step-by-Step Solution:
CoA → part of acetyl-CoA entry to the cycle.CO2 → product of oxidative decarboxylations.OAA → regenerated acceptor closing the cycle.FADH2 → produced at succinate dehydrogenase, feeding electrons to the ETC.Verification / Alternative check:Standard biochemical maps show these roles explicitly in the TCA cycle scheme.
Why Other Options Are Wrong:
b) Dark reactions use CO2 and NADPH; CoA and FADH2 are not Calvin cycle components.c) Lactic fermentation mainly involves pyruvate ↔ lactate and NADH ↔ NAD+.d) FADH2 participates in oxidative phosphorylation after being generated in the TCA cycle.e) The TCA cycle operates in both prokaryotes and eukaryotes.Common Pitfalls:Separating TCA from oxidative phosphorylation; they are linked via NADH/FADH2 supply.
Final Answer:They are all components or products of the citric acid cycle.
Discussion & Comments