Question

Which is true regarding the TCA cycle (Krebs cycle)? A. pyruvate is an end product of the cycle B. energy capture in the cycle is solely from the formation of ATP in one of the steps C. entry of carbon dioxide starts the cycle D. some components of the cycle are used as building blocks for certain anabolic pathways E. two of the above are true

Answer 1

Answer:

D. some components of the cycle are used as building blocks for certain anabolic pathways

Explanation:

Kreb's cycle starts when pyruvate enters the cycle in the form of acetyl CoA. The cycle completely breakdown acetyl CoA into CO2 and H2O. The released energy is stored in the form of NADH and FADH2 which enter oxidative phosphorylation to drive ATP synthesis. Kreb's cycle is an amphibolic pathway as it is involved in both catabolic and anabolic processes.

Some of the intermediates of Kreb's cycle serve as precursors for other anabolic pathways. For example, alpha-Ketoglutarate and oxaloacetate from Kreb's cycle enter the anabolic processes of synthesis of amino acids aspartate and glutamate respectively. Succinyl CoA from Kreb's cycle serves as one of the intermediates for the synthesis of porphyrin rings present in "heme" groups. The heme group is a structural and functional part of hemoglobin and myoglobin proteins.