Glycolysis II

Question 1

What is Reaction #5 catalyzed by?

Answer 1

Reaction #5 is catalyzed by the ‘perfect’ enzyme known as triose phosphate isomerase.

Question 2

What is the reason triose phosphate isomerase works so fast?

Answer 2

The reason the enzyme operates so fast is to prevent accumulation of a toxic intermediate.

Question 3

What is the product of Reaction #5?

Answer 3

The product of the reaction is G3P.

Question 4

What is the Delta G of Reaction #5 like?

Answer 4

The Delta G zero prime is close to zero, so this reaction is readily reversible. Everything after this step has two molecules of each.

Question 5

What is unique about Reaction #6?

Answer 5

Reaction 6 is the only oxidation in glycolysis.

Question 6

What is Reaction #6 catalyzed by?

Answer 6

It is catalyzed by glyceraldehyde-3-phosphate dehyrogenase.

Question 7

What is the energy of the oxidation used for in Reaction #6?

Answer 7

The energy of the oxidation is used to put phosphate onto the acid produced by the oxidation.

Question 8

What are the products of Reaction #6?

Answer 8

The products are NADH and 1,3 BPG. The latter has high energy (higher than ATP).

Question 9

What are the products of Reaction #7?

Answer 9

Reaction 7 produces 3PG and ATP, since the phosphate on 1,3BPG is transferred onto ADP. This enzyme is phosphoglycerate kinase.

Question 10

What is the ATP produced in reaction #7 a result of?

Answer 10

The ATP produced in this reaction is a result of substrate level phosphorylation. Another such phosphorylation occurs later in the cycle.

Question 11

What is Reaction #8 catalyzed by?

Answer 11

Reaction #8 is catalyzed by phosphoglycerate mutase and it simply involves rearrangement of the 3PG into 2PG.

Question 12

What is the Delta G of Reaction #8 like?

Answer 12

The Delta G zero prime is close to zero and the direction of the reaction is driven by cellular concentrations.

Question 13

Rearrangement of 3PG to 2PG involves creation _____

Answer 13

Rearrangement of 3PG to 2PG involves creation of an intermediate, 2,3 BPG, which is stable and can be released from the enzyme.

Question 14

Cells that are rapidly metabolize release ___ 2,3BPG, thus flagging hemoglobin of the location where rapid metabolism is occurring.

Answer 14

Cells that are rapidly metabolize release more 2,3BPG, thus flagging hemoglobin of the location where rapid metabolism is occurring.

Question 15

2,3 BPG can be made in blood cells from ___

Answer 15

2,3 BPG can be made in blood cells from 1,3 BPG by another mutase.

Question 16

What is the phosphoglycerate mutase reaction is more important?

Answer 16

The phosphoglycerate mutase reaction is more important because it is present in all cells and the amount of 2,3 BPG it produces is an indication of cellular metabolism levels.

Question 17

What is Reaction #9 catalyzed by?

Answer 17

Reaction #9 is catalyzed by enolase.

Question 18

What does Reaction #9 involve?

Answer 18

Reaction #9 involves removal of water from 2PG to form PEP, which is a compound containing high energy.

Question 19

Reaction #10 is the “____” of glycolysis.

Answer 19

Reaction #10 is the “Big Bang” of glycolysis.

Question 20

What is Reaction #10 catalyzed by?

Answer 20

It is catalyzed by the enzyme pyruvate kinase

Question 21

What does substrate level phosphorylation yield in Reaction 10? What is its Delta G like?

Answer 21

Substrate level phosphorylation yields ATP. Note that the Delta G zero prime is very strongly negative, helping to pull all the reactions preceding it to a large extent.

Question 22

Pyruvate kinase is regulated allosterically and by covalent modification. How does this work?

Answer 22

Covalent modification includes phosphorylation (inactivates) / dephosphorylation (activates).

The enzyme is activated allosterically by F1,6BP (activates), alanine (inhibits), and ATP (inhibits).

Question 23

Allosteric activation of pyruvate kinase by F1,6BP occurs as part of feedforward activation. What occurs in this process?

Answer 23

In this process, a molecule in a pathway activates an enzyme ahead of it in the same pathway. F1,6BP, of course is a product of the PFK reaction and accumulates when the aldolase reaction is slowed.

Accumulation of F1,6BP “pushes” the aldolase reaction forward. Activation of pyruvate kinase results in removal of PEP and all metabolites after the aldolase reaction, thus “pulling” the aldolase reaction. In this way, the aldolase reaction is favored, even though the reaction has a large positive delta G zero prime value.