7.2 Glycolysis - Biology for AP Courses

Overview

• Glycolysis is a crucial step in cellular respiration, breaking down glucose to extract energy.
• It occurs in the cytoplasm of both prokaryotic and eukaryotic cells and is considered one of the oldest metabolic pathways.
• Glycolysis does not require oxygen (anaerobic) and produces pyruvate, ATP, and NADH.

Learning Objectives

• Understand the molecular products from glucose breakdown via glycolysis.

Connection for AP Courses

• Glycolysis is a fundamental process used by nearly all organisms for energy extraction from glucose.
• It likely evolved early in life's history as a universal metabolic pathway.
• The process is independent of oxygen and occurs in the cytosol.

Glycolysis Process

First Half (Energy-Requiring Steps)

1. Step 1: Hexokinase phosphorylates glucose to glucose-6-phosphate using ATP, making it more reactive and trapping it within the cell.
2. Step 2: An isomerase converts glucose-6-phosphate to fructose-6-phosphate.
3. Step 3: Phosphofructokinase adds another phosphate, forming fructose-1,6-bisphosphate. This enzyme regulates the rate of glycolysis.
4. Step 4: Aldolase cleaves fructose-1,6-bisphosphate into two three-carbon isomers.
5. Step 5: Isomerase converts dihydroxyacetone phosphate into glyceraldehyde-3-phosphate.

Second Half (Energy-Releasing Steps)

6. Step 6: Glyceraldehyde-3-phosphate is oxidized, producing NADH, and phosphorylated to 1,3-bisphosphoglycerate (no ATP required).
7. Step 7: Phosphoglycerate kinase transfers a phosphate to ADP, forming ATP and 3-phosphoglycerate.
8. Step 8: Phosphoglycerate mutase rearranges 3-phosphoglycerate to 2-phosphoglycerate.
9. Step 9: Enolase dehydrates 2-phosphoglycerate to phosphoenolpyruvate (PEP).
10. Step 10: Pyruvate kinase transfers a phosphate from PEP to ADP, producing ATP and pyruvate.

Outcomes of Glycolysis

• Glycolysis starts with glucose, producing two pyruvate molecules, four ATP molecules, and two NADH.
• Net gain: 2 ATP, 2 NADH.
• Essential for cells that do not use aerobic respiration, like mature red blood cells.

Additional Notes

• Pyruvate kinase limits glycolysis rate; if insufficient, only minimal ATP is produced.
• Glycolysis's universality suggests it is one of the earliest metabolic pathways.

Think About It

• Nearly all organisms perform glycolysis, supporting it as a fundamental and ancient metabolic pathway.
• Red blood cells rely solely on glycolysis for ATP; blocking it could be fatal for these cells.

Teacher Support

• Discuss glycolysis’s conservation across life forms.
• Use visual aids to teach glycolysis stages.
• Highlight glycolysis's importance in energy extraction without oxygen.