Glycolysis and the Link Reaction
Glucose is split into two pyruvate molecules in the cytoplasm, with a small net ATP gain and no oxygen involved. Pyruvate then enters the mitochondrion and becomes acetyl coenzyme A.
What a learner can do afterwards
- Explains why glycolysis spends ATP before it yields any.
- States the net ATP and reduced NAD yield per glucose molecule.
- Says what is removed from pyruvate in the link reaction and where that happens.
1 · Read
Glycolysis opens respiration in the cytoplasm, breaking sugar to release energy for work such as movement, with no oxygen needed. One glucose is primed with two ATP, split into two three-carbon pieces, then oxidised into two pyruvates. The payoff banks four ATP and two reduced NAD, so after the two ATP entry fee the net gain is two ATP plus two reduced NAD.
Pyruvate cannot enter the next stage as it is, so the link reaction rebuilds it. Each pyruvate crosses into the mitochondrial matrix, loses carbon dioxide, and passes hydrogen to NAD. The leftover two-carbon acetyl group joins coenzyme A as acetyl CoA. Per glucose this runs twice, giving two carbon dioxides and two reduced NAD.
Keep a running tally per glucose. Glycolysis nets two ATP and two reduced NAD in the cytoplasm. The link step adds two carbon dioxides and two more reduced NAD in the matrix. Small gains now, bigger payoffs later. When oxygen runs short, fermentation recycles NAD in the cytoplasm so glycolysis keeps going.
A cell with no mitochondria still runs glycolysis, since the pathway lives in the cytoplasm. Fermenters recycle NAD in the cytoplasm to keep it spinning, while aerobes ship pyruvate toward the later stages.
Split glucose to two pyruvates for a net two ATP, then trim each pyruvate to acetyl CoA in the matrix.
2 · Watch
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Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.