Which of the following steps consumes ATP in glycolysis?

In glycolysis, ATP is consumed in the initial stages of the pathway, specifically during the phosphorylation of glucose and fructose-6-phosphate.

The first step involves the conversion of glucose to glucose-6-phosphate, which is catalyzed by the enzyme hexokinase (or glucokinase in the liver). This reaction requires the hydrolysis of ATP to provide a phosphate group, converting ATP into ADP. This is a key regulatory and energy-investing step, establishing glucose as a metabolite that can be further processed in glycolysis.

The third step features the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate, catalyzed by phosphofructokinase-1 (PFK-1), another critical regulatory step in glycolysis. Similar to the first step, this reaction also consumes ATP, which is used to add a second phosphate group to fructose-6-phosphate, thus helping to maintain the flow of the pathway.

Both steps 1 and 3 involve ATP consumption, making the choice that includes both steps the most accurate response to the question. The other steps mentioned in the options do not involve the consumption of ATP in the glycolytic pathway, making them irrelevant