Rucete ✏ Campbell Biology In a Nutshell
Unit 2 THE CELL — Concept 9.2 Glycolysis Harvests Chemical Energy by Oxidizing Glucose to Pyruvate
Glycolysis is the ancient, universal pathway through which cells break down glucose for energy. It occurs in the cytosol and yields ATP, NADH, and pyruvate without requiring oxygen.
1. Overview of Glycolysis
Location: Cytosol (cytoplasm)
Outcome: One glucose molecule is split into two pyruvate molecules.
Energy Harvest: Glycolysis generates a net of 2 ATP and 2 NADH per glucose.
2. Two Phases of Glycolysis
Energy Investment Phase
2 ATP are consumed to phosphorylate and rearrange glucose, preparing it for splitting.
Steps:
Glucose → glucose-6-phosphate (via hexokinase)
Rearranged to fructose-6-phosphate
Phosphofructokinase adds another phosphate → fructose-1,6-bisphosphate
Molecule is split into two 3-carbon sugars (G3P is the one that continues forward)
Energy Payoff Phase
4 ATP and 2 NADH are produced (net gain of 2 ATP)
G3P is oxidized and converted through several steps into pyruvate.
Key reactions:
NAD⁺ is reduced to NADH
Substrate-level phosphorylation yields ATP
3. Net Products of Glycolysis
2 Pyruvate
2 ATP (net)
2 NADH
4. What Happens to Pyruvate?
With oxygen (aerobic conditions): Pyruvate enters the mitochondria and continues through the citric acid cycle and oxidative phosphorylation.
Without oxygen (anaerobic): Pyruvate undergoes fermentation to regenerate NAD⁺ so glycolysis can continue.
In a Nutshell
Glycolysis is a 10-step metabolic pathway that converts glucose to pyruvate.
It works without oxygen, making it essential for all cells—especially anaerobic organisms and fast-acting tissues.
The process yields energy quickly and feeds into broader metabolic pathways for maximum ATP production.