Summary
Pyruvate is oxidised to acetyl-CoA in the mitochondrial matrix, releasing carbon dioxide and forming NADH.
In depth
Pyruvate dehydrogenase complex removes CO2 and reduces NAD+ to NADH, attaching the acetyl group to coenzyme A. Irreversible, so animals cannot convert fat to glucose. Inhibited by high acetyl-CoA and NADH.
The reaction links glycolysis to the Krebs cycle. It occurs in the mitochondrial matrix. Each glucose gives two acetyl-CoA, two CO2 and two NADH.
Remember: the reaction is irreversible in animals.
The link reaction connects glycolysis to the Krebs cycle. Pyruvate enters the mitochondrial matrix through a transporter, and the pyruvate dehydrogenase complex removes a carbon as CO2 (decarboxylation), oxidises the remainder (dehydrogenation), and attaches it to coenzyme A as acetyl-CoA, producing NADH.
Each glucose gives two pyruvates, so there are two turns: 2 CO2 and 2 NADH. It is an irreversible commitment of carbon to oxidation; animals cannot convert acetyl-CoA back into glucose. The complex is inhibited by its products and regulated by phosphorylation.
Example: thiamine (vitamin B1) deficiency impairs pyruvate dehydrogenase, causing beriberi.
Remember: it takes place in the matrix, not the cytoplasm.
Frequently asked questions
What is Link Reaction?
Pyruvate is oxidised to acetyl-CoA in the mitochondrial matrix, releasing carbon dioxide and forming NADH.
Which area of biology covers Link Reaction, and how advanced is it?
Link Reaction is one of the 53 topics in Metabolism & Bioenergetics. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Krebs Cycle, Beta-Oxidation, Cellular Respiration.
Can you give an example of Link Reaction?
Thiamine deficiency (beriberi) impairs this step.
What should I learn before Link Reaction?
Work through the Beginner topics in Metabolism & Bioenergetics first, such as Metabolism, Anabolism and Catabolism, ATP, then return to Link Reaction. Intermediate topics assume the Beginner vocabulary.
What topics are related to Link Reaction?
The closest topics to Link Reaction are Krebs Cycle, Beta-Oxidation, Cellular Respiration, Alcoholic Fermentation. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Link Reaction?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Link Reaction. To practise the whole of Metabolism & Bioenergetics, use the Metabolism & Bioenergetics quiz.
How is Link Reaction different from Krebs Cycle?
Link Reaction: Pyruvate is oxidised to acetyl-CoA in the mitochondrial matrix, releasing carbon dioxide and forming NADH. Krebs Cycle: A cyclic pathway that oxidises acetyl-CoA to carbon dioxide, producing NADH, FADH2 and a little ATP. Read both side by side and note what each one explains.
How should I study Link Reaction step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Krebs Cycle and explain the difference aloud. Finally, take the Metabolism & Bioenergetics quiz and come back to this page for any question you miss.