Question

Which of the following is the connecting link between glycolysis and the Krebs cycle?
A. Acetyl CoA
B. Oxalo succinic acid
C. Pyruvic acid
D. Citric acid

Answer 1

Hint: Glycolysis is the 1st step of cellular respiration and it is a common process for both aerobic and anaerobic respiration. It occurs in the absence of oxygen. The product of glycolysis is pyruvate which oxidizes into Acetyl CoA and acetyl CoA enters into mitochondria and takes part in Krebs cycle.

Complete answer:
In this question we have asked about the connecting link between glycolysis and krebs cycle. Glycolysis is the metabolic pathway in which, glucose C₆H₁₂O₆ converts into pyruvate, CH₃COCOO⁻, and a hydrogen ion, H⁺. The energy released in this process is used in ATP and NADH formation.
The final process of this process is pyruvic acid. This pyruvic acid converts into Acetyl CoA. This Acetyl CoA enters into mitochondria and starts the krebs cycle. The Krebs cycle is a series of chemical reactions used by all aerobic organisms to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.

> Option A is Acetyl CoA. Yes, we can say it is the connecting link between glycolysis and the Krebs cycle because it is acetylated pyruvic acid which is the end product of glycolysis and Acetyl CoA starts the Krebs cycle.
> Option B is oxalo succinic acid. Oxalo succinic acid is a substrate of the Krebs cycle and it is not related to glycolysis. So, we can’t call it the connecting link of glycolysis and the Krebs cycle. So, this option is wrong.
> Option C is pyruvic acid. As we already mentioned, pyruvic acid is an end product of glycolysis. It gets acetylated and converts into acetyl CoA which starts the krebs cycle. Yes it is connecting the both processes but we also have Acetyl CoA as an option which is a more appropriate answer than pyruvic acid.
> Option D is citric acid. Citric acid or citrate formation is the 1st step of the Krebs cycle, it is also not related to glycolysis. So, this option is also wrong.

The correct option is A. Acetyl CoA

Note: It is the transition reaction that connects glycolysis to the citric acid (Krebs) cycle. The transition reaction converts the two molecules of the 3-carbon pyruvate from glycolysis into two molecules of the 2-carbon molecule acetyl Coenzyme and 2 molecules of carbon dioxide.