Glycolysis, the Link Reaction, and the Krebs Cycle

Overview

This guide explores the three initial phases of cellular respiration, focusing on Glycolysis, the Link Reaction, and the Krebs Cycle.

Location & Nature
- Occurs in the cytoplasm
- Anaerobic process (does not require oxygen)
Phases of Glycolysis
1. Investment Phase
  - Glucose is phosphorylated using ATP, forming fructose-1,6-bisphosphate.
2. Cleavage Phase
  - Fructose-1,6-bisphosphate splits into two molecules of G3P (glyceraldehyde-3-phosphate).
3. Energy Harvest Phase
  - G3P is oxidized, transferring electrons to NAD+, forming NADH.
  - ATP is generated via substrate-level phosphorylation (4 gross ATP; net gain is 2 ATP after accounting for 2 ATP used in investment).
Outputs per Glucose
- 2 ATP
- 2 NADH
- 2 Pyruvate molecules

Process
- Connects glycolysis to the Krebs cycle and occurs in the mitochondrial matrix.
Steps
1. Pyruvate is transported into the mitochondria.
2. Enzymes remove a carbon dioxide from pyruvate (one-third of exhaled CO2).
3. The remaining 2-carbon molecule is oxidized, reducing NAD+ to NADH.
4. The acetyl group attaches to coenzyme A, forming acetyl-CoA, the starting molecule for the Krebs cycle.
Outputs per Pyruvate
- 1 NADH
Waste Product
- 1 CO2

Location
- Mitochondrial matrix.
Overview
- A cyclic series of reactions that oxidize acetyl-CoA, producing electron carriers and releasing CO2.
Key Points
1. Acetyl-CoA combines with oxaloacetate to form citrate.
2. Citrate and its byproducts undergo oxidation, transferring electrons to NAD+ (forming NADH) and FAD (forming FADH2).
3. One ATP is generated through substrate-level phosphorylation.
4. CO2 is released as a byproduct (two-thirds of exhaled CO2).
5. Oxaloacetate is regenerated to continue the cycle.
Outputs per Acetyl-CoA
- 1 ATP
- 3 NADH
- 1 FADH2
Waste Product
- 2 CO2

Videos and Quizzes
- Flashcards and quizzes available for further understanding and mastery.