Question 1

What happens when hexokinase phosphorylates glucose in glycolysis?

Accepted Answer

Hexokinase transfers a phosphate group from ATP to glucose, producing glucose 6-phosphate. The negatively charged phosphate group traps the molecule inside the cell because it cannot cross the hydrophobic cell membrane. This phosphorylation converts glucose into a more reactive form ready for subsequent glycolytic steps.

Question 2

Why is phosphofructokinase considered a rate-limiting enzyme in glycolysis?

Accepted Answer

Phosphofructokinase catalyzes the conversion of fructose 6-phosphate into fructose 1,6-bisphosphate, a critical control point in the energy-requiring phase. This enzyme regulates the overall rate of glycolysis by controlling when the unstable bisphosphate sugar is formed, determining how quickly glucose is processed through the pathway.

Question 3

How does aldolase split the sugar molecule during the energy-requiring phase?

Accepted Answer

Aldolase cleaves fructose 1,6-bisphosphate, which has two phosphate groups attached, into two 3-carbon isomers: glyceraldehyde 3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP). This splitting step is essential for converting one 6-carbon glucose molecule into two smaller 3-carbon sugars that proceed to the energy-releasing steps of glycolysis.

Question 4

What role does triosephosphate isomerase play in the energy-requiring phase?

Accepted Answer

Triosephosphate isomerase converts dihydroxyacetone phosphate (DHAP) into glyceraldehyde 3-phosphate (G3P). This conversion ensures that both 3-carbon products from aldolase cleavage are in the same form, yielding two molecules of G3P that can proceed identically through the remaining glycolytic pathway and subsequent cellular respiration.

Question 5

Why does the energy-requiring phase consume two ATP molecules?

Accepted Answer

Two ATP molecules are consumed during the energy-requiring phase: one by hexokinase to phosphorylate glucose into glucose 6-phosphate, and another by phosphofructokinase to phosphorylate fructose 6-phosphate into fructose 1,6-bisphosphate. These phosphate additions activate the glucose molecule and make it unstable enough to split into two 3-carbon sugars.

Question 6

How does phosphoglucose isomerase contribute to glycolysis progression?

Accepted Answer

Phosphoglucose isomerase catalyzes the conversion of glucose 6-phosphate into fructose 6-phosphate, one of its isomers. This isomerization is required for subsequent energy-requiring steps because fructose 6-phosphate is the substrate for phosphofructokinase, the rate-limiting enzyme that drives the pathway forward through cellular respiration.

Question 7

What is the net result of the energy-requiring phase of glycolysis?

Accepted Answer

The energy-requiring phase uses two ATP molecules to convert one glucose molecule into two 3-carbon sugars (G3P molecules). Although this phase consumes energy, it activates glucose and prepares it for the energy-releasing phase, where ATP is regenerated and the outcomes of glycolysis are produced.

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