The Link Reaction and Krebs Cycle

Following glycolysis, pyruvate enters the mitochondria where it is further oxidised in the link reaction and the Krebs cycle. These stages generate reduced coenzymes (reduced NAD and reduced FAD) and a small amount of ATP, while releasing CO₂ as a waste product. This lesson covers both stages in detail for the Edexcel A-Level Biology (9BI0) specification.

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Structure of the Mitochondrion

Before examining the biochemistry, it is essential to understand the mitochondrial structure, as this directly relates to function.

Structure	Description	Function
Outer membrane	Smooth, contains porins	Permeable to small molecules; defines the organelle
Inner membrane	Highly folded into cristae	Site of the electron transport chain and ATP synthase
Intermembrane space	Narrow space between membranes	Accumulates H⁺ ions for chemiosmosis
Matrix	Gel-like interior	Contains enzymes for the link reaction and Krebs cycle, mitochondrial DNA, ribosomes
Cristae	Folds of the inner membrane	Increase surface area for oxidative phosphorylation