Why do cells use two ATP at the beginning of glycolysis?
Glycolysis is a chain of reactions that results in the conversion of glucose into high energy compounds ATP and NADH.
There are ten steps that constitute the reactions which go on during the generation of energy from glucose. The first five steps are considered preparatory steps and involve the use of two ATP molecules. This converts glucose into three carbon sugar phosphates.
In the following 5 steps the products created after the initial steps are used, resulting in the formation of 2 NADH molecules and 4 ATP molecules. Therefore there is a net output of 2 ATP and 2 NADH molecules per molecule of glucose during glycolysis.