Role of the TCA (citric acid) cycle The tricarboxylic acid (TCA) cycle in living cells primarily functions as which type of pathway?

Introduction / Context:
The TCA cycle is central to metabolism. It oxidizes acetyl-CoA to CO2 while reducing NAD+ and FAD for ATP generation, yet it also provides key precursors for biosynthesis. The term that captures this dual role is important in biochemistry and microbiology curricula.

Given Data / Assumptions:

• Catabolism produces energy; anabolism consumes energy to build biomolecules.
• Intermediates of the TCA cycle feed into amino acid, nucleotide, and heme biosynthesis.
• Cells use anaplerotic reactions to refill TCA intermediates when diverted for anabolism.

Concept / Approach:

Because the TCA cycle simultaneously supports energy production (catabolic) and supplies precursors for biosynthesis (anabolic), it is classified as amphibolic. Microbes dynamically balance withdrawal of intermediates with anaplerotic reactions (for example, PEP carboxylase) to maintain flux.

Step-by-Step Solution:

Verification / Alternative check:

Textbooks consistently label the TCA cycle amphibolic due to its central position linking energy and biosynthetic metabolism.

Why Other Options Are Wrong:

• Catabolic only or anabolic only: Each captures part of the function but misses the duality.
• None of these/photolytic: Not applicable to the TCA cycle.

Common Pitfalls:

• Ignoring biosynthetic withdrawals when thinking of the TCA cycle purely as an energy pathway.

Final Answer:

amphibolic reactions