Glyceraldehyde-3-Phosphate Dehydrogenase

Definition

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a key enzyme involved in the glycolytic pathway, catalyzing the oxidation and phosphorylation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate. It plays a crucial role in both the processes of biological reductions and carbohydrate biosynthesis through gluconeogenesis.

5 Must Know Facts For Your Next Test

1. GAPDH catalyzes the reversible conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate, with the concomitant reduction of NAD+ to NADH.
2. The reaction catalyzed by GAPDH is an important step in glycolysis, providing a source of energy in the form of NADH and 1,3-bisphosphoglycerate.
3. During gluconeogenesis, GAPDH catalyzes the reverse reaction, converting 1,3-bisphosphoglycerate to glyceraldehyde-3-phosphate, a key intermediate in the synthesis of glucose.
4. GAPDH is considered a housekeeping gene, as it is constitutively expressed in all cells and is often used as a reference gene in gene expression studies.
5. In addition to its role in glycolysis and gluconeogenesis, GAPDH has been implicated in various other cellular processes, such as DNA repair, apoptosis, and transcriptional regulation.

Review Questions

• Explain the role of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in the glycolytic pathway.
  • GAPDH catalyzes a key step in glycolysis, the oxidation and phosphorylation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate. This reaction generates NADH, which can be used to produce ATP through the electron transport chain, and 1,3-bisphosphoglycerate, which can be further converted to pyruvate, the end product of glycolysis. GAPDH is essential for maintaining the flow of carbon through the glycolytic pathway and generating energy in the form of ATP.
• Describe the role of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in the process of gluconeogenesis.
  • During gluconeogenesis, GAPDH catalyzes the reverse reaction of its glycolytic function, converting 1,3-bisphosphoglycerate to glyceraldehyde-3-phosphate. This is a crucial step in the synthesis of glucose from non-carbohydrate precursors, such as amino acids, lactate, and glycerol. By providing glyceraldehyde-3-phosphate, GAPDH enables the completion of the gluconeogenic pathway, allowing the body to maintain blood glucose levels during periods of low carbohydrate intake or fasting.
• Analyze the significance of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in the context of both biological reductions and carbohydrate biosynthesis.
  • GAPDH plays a central role in the interplay between biological reductions and carbohydrate biosynthesis. In glycolysis, GAPDH catalyzes an oxidation-reduction reaction, converting glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate while reducing NAD+ to NADH. This NADH can then be used in the electron transport chain to generate ATP, the primary energy currency of the cell. Conversely, during gluconeogenesis, GAPDH catalyzes the reverse reaction, converting 1,3-bisphosphoglycerate to glyceraldehyde-3-phosphate, a key intermediate in the synthesis of glucose from non-carbohydrate precursors. This highlights the versatility of GAPDH in facilitating both catabolic and anabolic processes, underscoring its central importance in cellular metabolism.

Related terms

Glycolysis:

The metabolic pathway that converts glucose into pyruvate, producing a small amount of ATP in the process.

Gluconeogenesis:

The metabolic pathway that synthesizes glucose from non-carbohydrate precursors, such as amino acids, lactate, and glycerol.

Oxidation-Reduction Reactions: Chemical reactions in which the oxidation state of atoms is changed, involving the transfer of electrons.