Question

Discuss the concept of phosphorylation and dephosphorylation as an energy transfer in glycolysis. Why does the cell invest ATP and transfer a phosphate just to remove it in later steps within the glycolysis pathway?

Answer 1

When the substrate gains a phosphate group and the high energy molecule of ATP donates a phosphate group (producing a phosphorylated substrate and ADP), this process is known as phosphorylation. Kinase is a type of enzyme that catalyzes the transfer of phosphate groups from high-energy, phosphate-donating molecules to specific substrates.

While conversely, when the phosphorylated substrate donates a phosphate group and ADP gains a phosphate group (producing a dephosphorylated substrate and the high energy molecule of ATP), then it is called as dephosphorylation.

These two processes, phosphorylation and dephosphorylation, occur four times during glycolysis.

Glycolysis consists of two parts: The first part prepares the six-carbon ring of glucose for separation into two three-carbon sugars. Energy from ATP is invested into the molecule during this step to energize the separation. The second half of glycolysis extracts ATP and high-energy electrons from hydrogen atoms and attaches them to NAD+. Two ATP molecules are invested in the first half and four ATP molecules are formed during the second half. This produces a net gain of two ATP molecules per molecule of glucose for the cell.