ATP Production and Glycolysis

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Questions and Answers

Which of the following best describes substrate-level phosphorylation?

Phosphorylating ADP using phosphate directly from a substrate. (correct)
Adding phosphate to a substrate using ATP.
Generating free phosphate ions in the cytosol.
Using kinases to transfer phosphate groups between different molecules.

What is the role of phosphoglycerate kinase in glycolysis?

It removes a phosphate from phosphoenolpyruvate to form pyruvate.
It converts 1,3-bisphosphoglycerate into 3-phosphoglycerate, producing ATP. (correct)
It converts 3-phosphoglycerate into 2-phosphoglycerate.
It dehydrates 2-phosphoglycerate to form phosphoenolpyruvate.

How does arsenic poisoning affect glycolysis?

Arsenic inhibits pyruvate kinase directly.
Arsenic prevents the conversion of 3-phosphoglycerate to 2-phosphoglycerate.
Arsenic replaces inorganic phosphate in the glyceraldehyde-3-phosphate dehydrogenase (GA3P DH) reaction, preventing ATP production. (correct)
Arsenic blocks the initial phosphorylation of glucose by hexokinase.

What is the function of 2,3-DPG (diphosphoglycerate) in red blood cells (RBCs)?

It enhances the ability of hemoglobin to release oxygen. (C)

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Which enzyme is responsible for converting 2,3-bisphosphoglycerate back into 3-phosphoglycerate in RBCs?

2,3-bisphosphoglycerate phosphatase (B)

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What is the Rapoport-Leubering cycle?

The ability of RBCs to form 2,3-DPG. (C)

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Which of the following enzymes catalyzes the conversion of pyruvate to lactic acid in red blood cells?

Lactate dehydrogenase (C)

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How does 2,3-DPG affect the structure of hemoglobin A in adult humans?

It cross-links the beta chains, narrowing the oxygen pockets. (C)

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Which of these two inhibits pyruvate kinase?

Glucagon (A)

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Which of the following is the product of the reaction catalyzed by enolase?

Phosphoenolpyruvate (A)

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Considering a red blood cell with high levels of 2,3-DPG, what would be the expected impact on oxygen affinity?

Decreased oxygen affinity, promoting oxygen release. (A)

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In the context of arsenic poisoning, why does the modified reaction catalyzed by GA3P DH result in no ATP production?

Because the arsenic-containing intermediate spontaneously hydrolyzes, bypassing the substrate-level phosphorylation step. (D)

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If bisphosphoglycerate mutase is highly active in red blood cells, what immediate effect would this have on the glycolytic pathway?

Increased production of 2,3-DPG. (B)

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What is the significance of the conversion of NADH to $NAD^+$ during the reduction of pyruvate to lactic acid in RBCs?

It ensures a continuous supply of $NAD^+$ for glyceraldehyde-3-phosphate dehydrogenase, allowing glycolysis to proceed. (D)

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A researcher discovers a new drug that completely inhibits 2,3-bisphosphoglycerate phosphatase. How would this drug affect red blood cells?

Increase 2,3-DPG levels. (B)

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Flashcards

Substrate-level phosphorylation

Phosphorylating ADP using phosphate directly from a substrate molecule.

Phosphoglycerate kinase

Catalyzes the conversion of 1,3-Bisphosphoglycerate (1,3-BPG) to 3-Phosphoglycerate (3-PG), producing ATP.

Enolase

Converts 2-phosphoglycerate to phosphoenolpyruvate (PEP) by removing a water molecule.

Pyruvate kinase

Catalyzes the transfer of a phosphate group from phosphoenolpyruvate (PEP) to ADP, yielding pyruvate and ATP.

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Regulation of pyruvate kinase

Glucagon and ATP inhibit, while Fructose 1,6-bisphosphate stimulates its activity.

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Arsenic poisoning in glycolysis

Arsenic competes with inorganic phosphate (P_i) binding in glyceraldehyde-3-phosphate dehydrogenase (GA3P DH), preventing ATP production.

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Bisphosphoglycerate Mutase

Moves the phosphate from carbon 1 to carbon 2 of 1,3-BPG, forming 2,3-BPG.

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Function of 2,3-DPG in RBCs

It enhances oxygen release by hemoglobin.

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Mechanism of 2,3-DPG

It crosslinks beta chains in hemoglobin, reducing oxygen affinity.

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2,3-Bisphosphoglycerate Phosphatase

Converts 2,3-BPG back into 3-PG.

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Rapoport-Leubering Cycle

The process by which RBCs use bisphosphoglycerate mutase to form 2,3-DPG.

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Fate of pyruvate in RBCs

RBCs convert pyruvate to lactic acid, regenerating NAD+ from NADH.

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Study Notes

ATP Production and Phosphorylation

1,3-Bisphosphoglycerate (1,3 BP) loses a phosphate group from carbon 1.
This phosphate group attaches to ADP, forming ATP.
The product is 3-Phosphoglycerate.
This process occurs twice, resulting in 2 ATP molecules, which replace the ATP used by kinases in previous steps.
Substrate-level phosphorylation involves phosphorylating ADP using a phosphate group directly from a substrate molecule.
Phosphoglycerate kinase converts 1,3BP into 3-Phosphoglycerate (3P).

Further Glycolysis Steps

The phosphate group on 3-Phosphoglycerate is moved from the third carbon to the second carbon, resulting in 2-Phosphoglycerate (2P).
Enolase dehydrates 2-Phosphoglycerate to form Phosphoenolpyruvate.
Pyruvate kinase removes the phosphate group from Phosphoenolpyruvate and transfers it to ADP, producing ATP.
This step leaves pyruvate as the final product.
Pyruvate kinase is inhibited by glucagon and ATP.
Pyruvate kinase is stimulated by Fructose 1,6-bisphosphate.

Arsenic Poisoning

Arsenic interferes with enzymes in glycolysis.
Arsenic binds to the P_i (inorganic phosphate) binding pocket of Glyceraldehyde-3-phosphate dehydrogenase (GA3P DH).
Glyceraldehyde-3-phosphate (GA3P) binds to arsenic instead of inorganic phosphate (P_i).
This complex loses arsenic, directly forming 3-Phosphoglycerate without producing 1,3-Bisphosphoglycerate.
Consequently, no ATP is generated in this step.

2,3-Bisphosphoglycerate (2,3-DPG) in Red Blood Cells (RBCs)

Bisphosphoglycerate Mutase in RBCs moves the phosphate group from carbon 1 to carbon 2 of 1,3-Bisphosphoglycerate.
This produces 2,3-Bisphosphoglycerate (2,3-DPG).
2,3-DPG increases hemoglobin's ability to release oxygen.
Adult humans primarily use Hemoglobin A, composed of two alpha chains and two beta chains.
2,3-DPG cross-links the beta chains in hemoglobin.
This narrows the oxygen-binding pockets, promoting oxygen release.
2,3-Bisphosphoglycerate Phosphatase converts 2,3-BPG into 3-Phosphoglycerate (3P).

Rapoport-Luebering Cycle and RBC Metabolism

The Rapoport-Luebering Cycle describes the RBC's ability to form 2,3-DPG using bisphosphoglycerate mutase.
RBCs convert pyruvate into lactic acid using lactate dehydrogenase.
During this conversion, NADH is converted to NAD+.