Question

Connecting link between glycolysis and Krebs cycle is/before entering Krebs cycle pyruvate is changed to

• A. Oxaloacetate
• B. PEP
• C. Pyruvate
• D. Acetyl CoA

Answer 1

The correct option is D

Acetyl CoA

The correct option is D.
Explanation of the correct option:

1. Glycolysis is the process where glucose is converted into energy.
2. It produces two pyruvate molecules, ATP, NADH, and water.
3. The tricarboxylic acid (TCA) cycle, commonly known as the Krebs cycle or the citric acid cycle, is the primary source of energy for cells and an essential component of aerobic respiration.
4. The cycle converts acetyl coenzyme A's chemical energy into the reducing power of nicotinamide adenine dinucleotide (NADH).
5. Acetyl-CoA or Acetyl-Coenzyme A is the connection between glycolysis and the Krebs cycle.
6. The molecule, commonly known as CoASH or CoA, is an acetyl group carried by coenzyme A.

Explanation of the incorrect options:
Option A:

1. Oxaloacetate is a citric acid cycle intermediate that interacts with acetyl-CoA to generate citrate, which is catalyzed by citrate synthase.
2. It also participates in the urea cycle, the glyoxylate cycle, amino acid synthesis, and fatty acid synthesis.
3. Oxaloacetate is also a highly effective complex II inhibitor.
4. The cycle of citric acid (also called the Krebs cycle and the tricarboxylic acid cycle).
5. Initially, each acetyl CoA molecule is condensed with oxaloacetic acid to generate 6-C citric acid in the citric acid cycle.
6. Three molecules of NADH are produced for every acetyl CoA that enters the cycle.

Option B:

1. Phosphoenolpyruvate (2-phosphoenolpyruvate, PEP) is an ester formed by pyruvate and phosphate enols.
2. It exists in the form of an anion.
3. PEP is an essential biochemical intermediate.
4. It has the highest-energy phosphate bond discovered in organisms (61.9 kJ/mol) and is implicated in glycolysis and gluconeogenesis.
5. PEP carboxylase, like pyruvate carboxylase, replaces oxaloacetate in the citric acid cycle.
6. PEP is transformed to pyruvate at the end of glycolysis, which is then turned to acetyl-coenzyme-A (acetyl-CoA), which enters the citric acid cycle by interacting with oxaloacetate to generate citrate.

Option C:

1. Pyruvate is pyruvic acid's conjugate base.
2. It is an important intermediary in a variety of biological processes.
3. It is formed at the end of the glycolysis process and serves as a link between numerous metabolic processes such as gluconeogenesis, fermentation, cellular respiration, fatty acid synthesis, and so on.
4. Pyruvate is a biological substance and a result of glucose metabolism that combines with adenosine triphosphate and carbon dioxide at the start of the TCA cycle, turning it into acetyl-CoA and adenosine diphosphate (ADP).
5. It is frequently included in the cycle's introduction or preparatory step.

Final answer: The connecting link between glycolysis and Krebs cycle is/before entering Krebs cycle pyruvate is changed to Acetyl CoA.