Hexokinase: Glycolysis Step 1

Question 1

What is the first thing that happens to glucose when it enters the cell?

Answer 1

It is phosphorylated by ATP to form glucose 6-phosphate.

Question 2

What keeps glucose from leaving the cell once it has entered?

Answer 2

It is converted to G6P, which cannot pass through the cell membrane (because it is not a substrate for the glucose transporters).

Question 3

What enzyme catalyzes the transfer of the phosphoryl group from ATP to the hydroxyl group on carbon 6 of glucose to convert glucose into G6P?

Answer 3

Hexokinase

Question 4

What are enzymes that catalyze the transfer of a phosphoryl group to an acceptor?

Answer 4

Kinases

Question 5

What cofactor does hexokinase require to be a haloenzyme?

Answer 5

Mg2+

Question 6

What cofactor do all kinases require to be active?

Answer 6

Mg2+

Question 7

What happens when hexokinase binds glucose?

Answer 7

Binding of glucose yields a conformation change in which the two lobes of hexokinase move together, surrounding all of the glucose molecule except for the carbon atom that will accept the phosphoryl group (creates an induced fit). This environment around glucose becomes more non-polar, removing water and favoring the donation of the terminal ATP phosphate to glucose.

Question 8

What would happen if hexokinase were rigid and H2O were able to occupy the binding site?

Answer 8

It could attack ATP, forming ADP and Pi (i.e., the kinase would be an ATPase).

Question 9

What inhibits hexokinase? What kind of inhibitor is it?

Answer 9

ATP; an allosteric inhibitor

Question 10

What happens if water is present with ATP?

Answer 10

It reacts to form ADP and Pi

Question 11

What does Mg2+ (a divalent metal ion) form a complex with in hexokinase?

Answer 11

ATP