Question

Correct sequence of steps of citric Acid Cycle: A. Succinyl CoA, B. Acetyl CoA, C. Citrate, D. $\alpha$-ketoglutarate, E. Malate Choose the correct answer from the options given below:

• A. A, B, C, D, E \
• B. B, C, D, A, E \
• C. E, A, D, B, C \
• D. A, C, B, E, D

Hint:

Remember the classic phrase: "Acetyl Citrate Killed Succinyl's Mother" to easily remember the order: Acetyl CoA $\rightarrow$ Citrate $\rightarrow$ $\alpha$-Ketoglutarate $\rightarrow$ Succinyl CoA $\rightarrow$ Malate.

Answer 1

The Correct Option is B

Step 1: Concept The Citric Acid Cycle (Krebs cycle) is a closed loop of eight metabolic reactions that takes place inside the mitochondrial matrix to oxidize acetyl units into carbon dioxide.

Step 2: Meaning The intermediates flow sequentially as carbons are modified, oxidized, and rearranged to regenerate the starting oxaloacetate molecule.

Step 3: Analysis Let us follow the cyclical path using the provided steps: 1. The cycle starts when Acetyl CoA (B) enters the mitochondrion and condenses with oxaloacetate. 2. This condensation reaction forms the 6-carbon molecule Citrate (C). 3. After conversion to isocitrate, oxidative decarboxylation produces the 5-carbon intermediate $\alpha$-ketoglutarate (D). 4. A second oxidative decarboxylation reaction produces the 4-carbon compound Succinyl CoA (A). 5. After several downstream conversions through succinate and fumarate, the cycle generates Malate (E).

Step 4: Conclusion The chronological sequence of these intermediates is B $\rightarrow$ C $\rightarrow$ D $\rightarrow$ A $\rightarrow$ E. This aligns with option B. Final Answer: (B)