Question

1. in the first step of glycolysis, glucose becomes glucose 6 - phosphate. where does the phosphate on the sixth carbon of glucose come from? similarly, in the third step, when fructose 6 phosphate becomes fructose 1,6 bisphosphate, where does the additional phosphate group on the first carbon of fructose come from?

Explanation:

Step1: Analyze the first step of glycolysis

In the first step, glucose is phosphorylated to glucose - 6 - phosphate. The phosphate group comes from ATP. The reaction is catalyzed by hexokinase (or glucokinase in the liver). The general reaction is \( \text{Glucose}+\text{ATP}\xrightarrow{\text{hexokinase}}\text{Glucose - 6 - phosphate}+\text{ADP} \).

Step2: Analyze the third step of glycolysis

In the third step, fructose - 6 - phosphate is phosphorylated to fructose - 1,6 - bisphosphate. The phosphate group also comes from ATP. The reaction is catalyzed by phosphofructokinase - 1. The general reaction is \( \text{Fructose - 6 - phosphate}+\text{ATP}\xrightarrow{\text{phosphofructokinase - 1}}\text{Fructose - 1,6 - bisphosphate}+\text{ADP} \).

Answer:

In the first step, the phosphate on the sixth carbon of glucose comes from ATP. In the third step, the additional phosphate group on the first carbon of fructose comes from ATP.