The name of the enzyme that catalyses the conversion of glucose to glucose-6-phosphate at the beginning of glycolysis is

Analyze the question: The question asks which enzyme starts glycolysis by converting glucose into glucose-6-phosphate.

Explain the concept: Glycolysis is the breakdown of glucose (6C) into two pyruvate molecules (3C) in the cytoplasm. The first stage is the "investment phase," where ATP is used to prepare glucose for splitting. In the first step, a phosphate group from ATP is added to carbon 6 of glucose. Enzymes that transfer phosphate groups are called kinases.

Step-by-step solution:

1. Step 1 of glycolysis: Glucose + ATP → Glucose-6-phosphate + ADP This reaction is catalysed by hexokinase. It acts on hexose (6-carbon) sugars, which is where the name comes from.

2. Step 2: Glucose-6-phosphate is converted to fructose-6-phosphate by phosphoglucose isomerase.

3. Step 3: Fructose-6-phosphate is converted to fructose-1,6-bisphosphate by phosphofructokinase.

Checking the options:

• A. Phospho-fructokinase: this acts at step 3, on fructose-6-phosphate, so it is wrong.
• B. Glucose isomerase: this is not the enzyme for this step. Isomerases rearrange molecules and do not add phosphate from ATP.
• C. Hexokinase: this is correct. It phosphorylates glucose at the start of glycolysis.
• D. Glucose-6-kinase: this is not a standard name for this enzyme.

Tip: Remember the first three steps with "How People Phosphorylate": Hexokinase → Phosphoglucose isomerase → Phosphofructokinase. Also, any enzyme ending in "-kinase" in glycolysis adds a phosphate using ATP.