Chapter 7, Problem 1TY

Which of the following pathways occurs in the cytosol?

1. a. glycolysis
2. b. breakdown of pyruvate to an acetyl group
3. c. citric acid cycle
4. d. oxidative phosphorylation
5. e. all of the above

Summary Introduction

Introduction: Conversion of glucose molecules to pyruvate molecules and the production of energy in the form of ATP and NADH occur through glycolysis. It is used for the cellular respiration of the cell through redox reactions. It may follow either the anaerobic pathway or the aerobic pathway to do so.

Answer to Problem 1TY

Correct answer: Glycolysis occurs in the cytosol. Hence, the correct answer is option a.

Explanation of Solution

Reason for correct answer:

Glycolysis occurs through two main stages. In the first phase, two molecules of glyceraldehyde-3-phosphate are produced from glucose. In the second phase, the molecules of glyceraldehyde-3-phosphate are converted to pyruvate. Both of these stages occur in the cytoplasm of the cell.

Option a. is given as “glycolysis”

The process of glycolysis occurs in the cytosol of cells. Hence, the correct answer is option a.

Reasons for incorrect answer:

Option b. is given as, “breakdown of pyruvate to an acetyl group”.

The outcome of glycolysis is pyruvate. It enters the mitochondria of the cell and is broken down to give acetyl molecules. The breakdown of pyruvate to an acetyl group occurs in the mitochondria. Hence, option b. is incorrect.

Option c. is given as, “citric acid cycle”.

The breakdown of pyruvate to an acetyl group occurs in the mitochondria. Further, acetyl coenzyme A reacts with oxaloacetate and enters the citric acid cycle. Citrate is produced by the reaction of acetyl coenzyme A and oxaloacetate. The citric acid cycle occurs in the mitochondria. Hence, option c. is incorrect.

Option d. is given as, “oxidative phosphorylation”.

Oxidative phosphorylation is the process by which electrons are transferred from NADH or FADH₂ to oxygen molecules. This happens through a series of steps in which it passes though many electron carriers and results in the formation of ATP molecules. This occurs by the help of the enzyme ATP synthase present on the mitochondrial membrane. Hence, option d. is incorrect.

Option e. is given as, “all of the above”.

Breakdown of pyruvate to acetyl group and the citric acid cycle occur in the mitochondria and oxidative phosphorylation occurs in the mitochondrial membrane. Only glycolysis, represented by option a. occurs in the cytosol. Hence, option e. is incorrect.

Hence, the options b., c., d., and e. are incorrect.

Conclusion

Thus, glycolysis occurs in the cytosol in two phases. Breakdown of pyruvate to acetyl group and the citric acid cycle occur in the mitochondria and oxidative phosphorylation occurs in the mitochondrial membrane.