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Medical Biology & Molecular Genetics
Medical BiologyLesson 2 of 2

Cell Respiration & Oxidative Phosphorylation

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Pyruvate FormationSubstrate PhosphorylationGlycolysisNADH ProductionFADH2 ProductionKrebs CycleElectron Transport ChainATP SynthaseOxidative PhosphorylationCell Respiration
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Part 1 of 3

1. Glycolysis & Energy Investment

Glycolysis is the first stage of cellular respiration and occurs in the cytoplasm. It does not directly require oxygen because it is an anaerobic pathway. A single glucose molecule containing six carbon atoms is converted into two pyruvate molecules containing three carbons each.

The process has two phases. The energy investment phase uses 2 ATP molecules to activate glucose. The energy payoff phase produces 4 ATP molecules and 2 NADH molecules. The final net result is therefore 2 ATP and 2 NADH per glucose molecule.

IMAT often tests whether you confuse total ATP production with net ATP gain. Always subtract the ATP used at the beginning.

Worked example

A cell processes 3 glucose molecules through glycolysis. Each glucose molecule gives a net gain of 2 ATP. Therefore total ATP produced directly by glycolysis is 3 × 2 = 6 ATP molecules. The pathway also produces 6 NADH molecules.

1.Glycolysis occurs in the cytoplasm of the cell.

2.The net ATP production of glycolysis from one glucose molecule is 4 ATP.

Exam strategy

If you can explain why the wrong answers are wrong, you know the topic. Remembering the right one only gets you halfway.

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