Question

All intermediates in glycolysis have a phosphate group attached to them except glucose and pyruvate. Why does phosphorylation of glucose take place during glycolysis?

• A. No intermediate will escape the cell even if there is a concentration difference inside and outside the cell
• B. Phosphorylated intermediate compounds act as energy donors
• C. Binding of a phosphate group helps the enzyme to carry out the reaction
• D. All of the above

Answer 1

The correct option is D All of the above

The pathway of the breakdown of glucose into pyruvic acid is termed as glycolysis. This pathway is a step-wise process in which all molecules except glucose and pyruvate bear phosphate group. The steps are:


There are several reasons behind the addition of phosphate group to the reaction intermediates:

i) Plasma membrane bears different transport proteins for carrying different molecules. However, plasma membrane lacks any transporter for phosphorylated compounds. Hence, no intermediate will escape the cell even if there is a concentration difference inside and outside the cell.

ii) In the energy-yielding steps of the glycolysis, the release of energy from the phospho compounds during the breakdown of phosphate bond is stored as ATP. This occurs by donation of the phosphate group to adenosine diphosphate to form adenosine triphosphate.

iii) Enzymes are required to carry out metabolic reactions such as glycolysis reactions. The binding of a phosphate group helps the enzyme to carry out the reactions.