How are glycolysis, TCA cycle and electron transport chain-linked? Explain.

Glycolysis, TCA cycle and electron transport chain are linked in the following manner:

1. The coenzymes are initially present in the form of NAD⁺ and FAD⁺ which latter get reduced to NADH+H⁺ and FADH+H⁺ by accepting the hydrogen from organic substrate during glycolysis, link reaction and Krebs cycle. 

2. During glycolysis, glucose is oxidised to two molecules of pyruvic acid with net gain 2 molecules of NADH+H⁺ . 

3. This pyruvic acid undergoes link reaction to form two molecules of acetyl COA and two molecules of NADH+H⁺ . 

4. Acetyl COA, thus formed enters into the Krebs cycle and it gets completely oxidised to CO₂ and H₂O; with a net gain of 6 NADH+H⁺ and 2 FADH+H⁺ are formed. 

5. During ETS, reduced coenzymes are reoxidized to NAD⁺ and FAD⁺ with a net gain of 34 ATPs. The ATPs thus formed are used during glycolysis.

6. The oxidized NAD⁺ and FAD⁺ will again accept the hydrogen from organic substrate. Thus, reduced coenzymes are converted back to their oxidized forms by dehydrogenation to keep the process going.