Chapter 5, Problem 1aCP

Define the term glycolysis in terms of its initial substrates and products. Explain why there is a net gain of 2 molecules of ATP in this process.

Summary Introduction

To review:

The definition of glycolysis in terms of its initial substrates and products along with the reason for the net gain of two molecules of ATP in the process.

Introduction:

Cellular respiration is a process in which energy is released by stepwise break down of glucose and other molecules through which energy is consumed, and some of this energy is used to produce ATP (adenosine triphosphate), that is, the energy currency for every cell. The complete combustion of a glucose molecule requires oxygen and yields about 38 ATP for each molecule of glucose. Some of the energy is produced in the absence of an oxygen requiring pathway that leads to the generation of lactic acid as an end product.

Explanation of Solution

The first cellular respiration process for the breakdown of glucose is glycolysis, which is a process of breakdown of glucose (a 6-carbon compound) into the two molecules of pyruvate or pyruvic acid (a 3-carbon compound). The diagram belowshows the different steps in the breakdown of glucose:

Glycolysis is a 10-step process and in every step, enzymes are required to catalyze the reaction. The 6-carbon molecule is the substrate which results in the production of two molecules of 3-carbon pyruvic acid (pyruvate).

The pathway requires two ATP molecules as a source of energy, one for the conversion of glucose into glucose-6-phosphate and the second for the conversion of fructose-6-phosphate into the fructose-1,6-bisphosphate.

The glycolysis pathway generates 2 molecules of NADH (nicotinamide adenine dinucleotide hydrogen) and 4 molecules of ATP, 2 ATP molecules are expended during the process, so there is a net gain of 2 ATP molecules.