Glycolysis Overview and Processes

Glycolysis Overview

• Glycolysis is the breakdown of glucose (a 6-carbon molecule) into two molecules of pyruvate (a 3-carbon molecule).
• It's a metabolic pathway converting glucose to energy and intermediates for other metabolic pathways.
• It's an anaerobic process, meaning it doesn't require oxygen, but the presence or absence of oxygen affects the fate of pyruvate.
• It's the first step in cellular respiration, preceding the Krebs Cycle and the Electron Transport Chain (ETC).
• Glycolysis occurs in the cytoplasm of the cell.
• With oxygen, pyruvate enters the Krebs Cycle; without oxygen, it's converted to lactate.

Inputs and Outputs

• Inputs: One glucose molecule, 2 ATP molecules, and 2 NAD+ molecules.
• Outputs: Two pyruvate molecules, 2 ADP molecules, and 2 NADH molecules.

Glycolysis Steps

• Phosphorylation (Hexokinase): A dehydrogenase enzyme is used to oxidize and phosphorylate Glyceraldehyde-3-Phosphate, forming 1,3-Bisphosphoglyceric acid. The phosphate comes from NAD+.
• Oxidative Phosphorylation: A phosphate group from 1,3-Bisphosphoglyceric acid is transferred to ADP, forming ATP and 3-Phosphoglyceric acid. This reaction is catalyzed by phosphoglycerate kinase. The source of the inorganic phosphate in this step is not NADPH, but is a result of a high-energy phosphate bond being transferred.
• Transfer of Phosphate Group (Phosphoglycerate Mutase): The phosphate group is moved to the second carbon atom, producing 2-Phosphoglyceric acid, catalyzed by phosphoglycerate mutase.
• Dehydration (Enolase): 2-Phosphoglyceric acid loses a water molecule to produce Phosphoenolpyruvate. The enzyme responsible is enolase.
• Transfer of Phosphate Group (Pyruvate Kinase): A final ATP molecule is produced when a phosphate group from Phosphoenolpyruvate is transferred to ADP, creating pyruvate. The enzyme catalyzing this step is pyruvate kinase.