Biology · Respiration in Plants · NEET
Hexokinase. It transfers a phosphate group from ATP onto glucose, making glucose-6-phosphate. NCERT (Ch 12) says both glucose and fructose are phosphorylated to glucose-6-phosphate by the enzyme hexokinase. This is the first reaction of the EMP (glycolysis) pathway and it happens in the cytoplasm.
It USES (spends) 1 ATP. Glycolysis has an early investment phase where energy is put in before energy is later collected. NCERT states ATP is utilised at two steps, and the FIRST is the conversion of glucose into glucose-6-phosphate. So the hexokinase step is an ATP-consuming step, not an ATP-making step.
Two reasons. First, phosphorylation traps glucose inside the cell because the charged glucose-6-phosphate cannot leak back out through the membrane. Second, adding phosphate makes the molecule more reactive (activated), so the next steps of glycolysis can proceed. This is why the cell spends 1 ATP even though glycolysis is meant to release energy.
It is irreversible. NEET 2019 directly called it 'the first irreversible reaction of glycolysis.' Because it is committed and one-way, it acts as a control point of the pathway. This is a common NEET fact — remember it as the first committed (irreversible) step.
Both use ATP, but they act on different molecules. Hexokinase acts FIRST: glucose to glucose-6-phosphate. Phosphofructokinase acts LATER: fructose-6-phosphate to fructose-1,6-bisphosphate. NEET often mixes these two up, so link 'hexo = glucose (first)' and 'phospho-fructo = fructose (second).'
It isomerises (rearranges) into fructose-6-phosphate. NCERT says the phosphorylated form of glucose then isomerises to produce fructose-6-phosphate, and from there glucose and fructose follow the same steps. So glucose-6-phosphate is a short-lived link between glucose entry and the main glycolytic chain.
Conversion of glucose to glucose-6-phosphate, the first irreversible reaction of glycolysis, is catalyzed by
Assertion A: ATP is used at two steps in glycolysis. Reason R: First ATP is used in converting glucose into glucose-6-phosphate and second ATP is used in conversion of fructose-6-phosphate into fructose-1,6-diphosphate. In the light of the above statements, choose the correct answer.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
In the cytoplasm. All ten reactions of glycolysis, including this first step, happen in the cytoplasm of the cell and are present in all living organisms.
Two ATP are invested — one at the hexokinase step (glucose to glucose-6-phosphate) and one at the phosphofructokinase step (fructose-6-phosphate to fructose-1,6-bisphosphate).
Yes. NCERT says glucose and fructose are both phosphorylated to give glucose-6-phosphate by hexokinase, after sucrose is split into glucose and fructose by invertase.
Because it is irreversible and once glucose is phosphorylated it is locked into the glycolytic pathway. This makes it an important control point of glycolysis for NEET.
