What is the process of glycolysis, and how is glucose converted to pyruvate in the cytoplasm?

Sourav PanNovember 9, 2024

Answered

Glycolysis is a crucial metabolic pathway that converts glucose into pyruvate, occurring in the cytoplasm of cells. This process involves a series of enzyme-catalyzed reactions and can be divided into two main phases: the energy investment phase and the energy payoff phase.

Overview of Glycolysis

• Location: Glycolysis takes place in the cytoplasm of both prokaryotic and eukaryotic cells.
• Overall Reaction: The simplified equation for glycolysis is:
  Glucose+2NAD++2ADP+2Pi→2Pyruvate+2NADH+2ATP+2H2O

Phases of Glycolysis

1. Energy Investment Phase

In this initial phase, energy is consumed to prepare glucose for subsequent breakdown:

1. Phosphorylation of Glucose:
   • Enzyme: Hexokinase
   • Reaction: Glucose is phosphorylated to form glucose-6-phosphate (G6P) using one ATP molecule.
   • Significance: This step traps glucose in the cell and prepares it for further breakdown.
2. Isomerization:
   • Enzyme: Phosphoglucose isomerase
   • Reaction: G6P is converted into fructose-6-phosphate (F6P).
3. Second Phosphorylation:
   • Enzyme: Phosphofructokinase (PFK)
   • Reaction: F6P is phosphorylated to form fructose-1,6-bisphosphate (F1,6BP) using another ATP molecule.
   • Significance: This is a key regulatory step in glycolysis.
4. Cleavage:
   • Enzyme: Aldolase
   • Reaction: F1,6BP is split into two three-carbon molecules: glyceraldehyde-3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP).
5. Interconversion:
   • Enzyme: Triose phosphate isomerase
   • Reaction: DHAP is converted into G3P, resulting in two G3P molecules available for the next phase.

2. Energy Payoff Phase

In this phase, ATP and NADH are produced:

1. Oxidation and Phosphorylation:
   • Enzyme: Glyceraldehyde-3-phosphate dehydrogenase
   • Reaction: Each G3P molecule is oxidized, reducing NAD+ to NADH and forming 1,3-bisphosphoglycerate (1,3-BPG).
2. ATP Generation (Substrate-Level Phosphorylation):
   • Enzyme: Phosphoglycerate kinase
   • Reaction: 1,3-BPG donates a phosphate to ADP to form ATP and produces 3-phosphoglycerate (3-PG).
3. Conversion Steps:
   • The following reactions involve rearrangements and dehydration:
     • Conversion of 3-PG to 2-phosphoglycerate (2-PG).
     • Conversion of 2-PG to phosphoenolpyruvate (PEP) via enolase.
4. Final ATP Generation and Pyruvate Formation:
   • Enzyme: Pyruvate kinase
   • Reaction: PEP donates its phosphate to ADP to produce another ATP and forms pyruvate as the end product.