Glycolysis Step 5: Glyceraldehyde-3-phosphate Dehydrogenation

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Questions and Answers

What is the product of the dehydrogenation and phosphorylation reaction in step 5 of glycolysis?

Glyceraldehyde-3-phosphate

1,3-bisphosphoglycerate (correct)

3-phosphoglycerate

Phosphoenol pyruvate

What is the function of NAD+ in step 5 of glycolysis?

To donate a phosphate group

To accept an electron and get reduced (correct)

To synthesize ATP

To inhibit the enzyme glyceraldehyde-3-phosphate dehydrogenase

What type of phosphorylation occurs in step 6 of glycolysis?

Electron transport chain

Fermentation

Oxidative phosphorylation

Substrate level phosphorylation (correct)

What is the function of phosphoglucomutase in step 7 of glycolysis?

To isomerize 3-phosphoglycerate to 2-phosphoglycerate Signup and view all the answers

What is the effect of fluoride on enolase in step 8 of glycolysis?

It inhibits the enzyme irreversibly Signup and view all the answers

What is the product of the reaction catalyzed by pyruvate kinase?

Keto pyruvate Signup and view all the answers

Why is fluoride added to blood when taking it for sugar estimation?

To inhibit the metabolism of glucose by blood cells Signup and view all the answers

Why is step 10 of glycolysis necessary in anaerobic conditions?

To regenerate NAD+ from NADH Signup and view all the answers

What is the reactant that is converted to pyruvate in step 9 of glycolysis?

Phosphoenol pyruvate Signup and view all the answers

What is the significance of lactate production in glycolysis?

It is necessary for the regeneration of NAD+ in anaerobic conditions Signup and view all the answers

What is the type of reaction that occurs in step 6 and step 8 of glycolysis?

Substrate level phosphorylation Signup and view all the answers

What is the purpose of the reaction catalyzed by lactate dehydrogenase?

To reduce pyruvate to lactate Signup and view all the answers

Why does the cell need to couple steps 5 and 10 of glycolysis?

To regenerate NAD+ in anaerobic conditions Signup and view all the answers

What is the end product of anaerobic glycolysis?

Lactate Signup and view all the answers

Why do red blood cells derive energy only through glycolysis?

Because they lack mitochondria Signup and view all the answers

What is the fate of lactate produced in anaerobic glycolysis?

It enters the Cori's cycle Signup and view all the answers

Study Notes

Step 5 of Glycolysis

Glyceraldehyde-3-phosphate is dehydrogenated and phosphorylated to 1,3-bisphosphoglycerate (1,3-BPG) with the help of NAD+.
This reaction is reversible and has a high-energy bond.
The enzyme involved is glyceraldehyde-3-phosphate dehydrogenase.
NAD+ is reduced to NADH during this reaction.

Step 6 of Glycolysis

The energy of 1,3-BPG is trapped to synthesize one ATP molecule with the help of bisphosphoglycerate kinase.
This is an example of substrate-level phosphorylation.
The reaction is reversible.

Step 7 of Glycolysis

3-phosphoglycerate is isomerized to 2-phosphoglycerate by shifting the phosphate group from the 3rd to the 2nd carbon atom.
The enzyme involved is phosphoglucomutase.
This reaction is readily reversible.

Step 8 of Glycolysis

2-phosphoglycerate is converted to phosphoenolpyruvate by the enzyme enolase.
One water molecule is removed, and a high-energy phosphate bond is produced.
The reaction is reversible, and enolase requires Mg++.
Fluoride inhibits enolase irreversibly.

Step 9 of Glycolysis

Phosphoenolpyruvate (PEP) is dephosphorylated to pyruvate by pyruvate kinase.
One mole of ATP is generated during this reaction.
This is an example of substrate-level phosphorylation.
The pyruvate kinase is a key glycolytic enzyme, and this step is irreversible.

Step 10 of Glycolysis

In anaerobic conditions, pyruvate is reduced to lactate by lactate dehydrogenase (LDH).
LDH has five iso-enzymes, and the cardiac iso-enzyme will be increased in myocardial infarcts.

Significance of Lactate Production

Steps 5 and 10 are coupled, and the regeneration of NAD+ is essential for smooth operation of the glycolytic pathway.
In aerobic conditions, pyruvate enters the citric acid cycle for complete oxidation, while in anaerobic conditions, lactate enters the Cori's cycle.
In RBCs, which lack mitochondria, glycolysis is the only source of energy production, and the end product is lactic acid.

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Description

Learn about the 5th step of glycolysis, where glyceraldehyde-3-phosphate is dehydrogenated and phosphorylated to 1,3-bisphosphoglycerate with the help of NAD+. Understand the role of glyceraldehyde-3-phosphate dehydrogenase and the high energy bond formation.