Question

Explain the benefit of the TCA cycle in detail.

Answer 1

TCA(Tricarboxylic acid cycle) also known as citric acid cycle or the Krebs cycle is complex cycle in which series of chemical reactions occur to release stored energy by the oxidation of acetyl-CoA(acetyl coenzyme A) derived from carbohydrate,fats and proteins into ATP(adenosine triphosphate) and CO2 . In this initially acetyl CoA(2 carbon compound) binds to OAA(oxalo acetic acid,a 4 carbon compound) to form citric acid which ultimately releases all carbon atoms of acety- CoA by forming many intermediates and finally OAA regenerates.  This cycle also provides precursors of certain amino acids,and reducing agent NADH(nicotinamide adenine dinucleotide) as well as FADH2 that are used in oxidative phosphorylation of ETS(electron transport system which occurs in inner mitochondrial membrane).

This cycle occurs in all aerobic organisms in the matrix of their mitochondria.

Benefits of TCA are follows:-

1.TCA act as a final common pathway and this cycle plays a central role in the breakdown of carbohydrates,fats and proteins to release mainly ATP and NADH.

2. If there is deficiency of glucose than this cycle can derive energy from other sources also more preferably from fats and less preferably from proteins.

3.It's the second of the three stages of cellular respiration and eventually connects all catabolic pathway of carbohydrates,fats and proteins,further this act as connecting link to ETS(metabolic pathway to release and utilise energy for ATP synthesis from NADH + H+ and FADH2.

4.Some TCA cycle intermediates also act as a intermediate for biosynthesis of glucose,fatty acids, amino acids,some steroid hormones,cholesterol,vitamin-D,bile salts,etc.

5. Particularly by taking acetyl CoA with citrate outside of mitochondria this acetyl CoA is used for fatty acid synthesis and cholesterol.

6.This cholesterol is used to synthesise bile salts,vitamin D,etc.

7. OAA of TCA form aspartate and asparagine and alpha keto glutaric acid of TCA form arginine,glutamine,etc.

8. These aspartate and glutamine are used to form purines that are used as a base in DNA and RNA.

9. Each glucose molecules requires two turns of TCA and each TCA gives finally,6NADH,2FADH2 and 2ATP(GTP).Therefore it is important for cellular energy needs.

10.Several catabolic pathway converge on TCA and most of their reactions add intermediate to TCA,thus increase the mitochondrial ability.

Due many functions of TCA it is considered as a "central hub of metabolism".