Concept preview

What you will be able to do

1. 01Describe the link reaction that converts pyruvate into acetyl-CoA, releasing carbon dioxide and making NADH.
2. 02Explain where the Krebs (citric acid) cycle takes place and what it produces.
3. 03Identify the products of the Krebs cycle: carbon dioxide, NADH, FADH2, and a little ATP/GTP.
4. 04Explain why the link reaction and the Krebs cycle each run twice per glucose molecule.

At the end of glycolysis the cell holds two molecules of pyruvate, still rich in energy, floating in the cytoplasm. When oxygen is available, those pyruvate molecules do not linger; they are carried across two membranes into the innermost compartment of the mitochondrion, a fluid-filled space called the matrix. The mitochondrion is often called the powerhouse of the cell, and the matrix is where the next two great stages of respiration unfold. Here the cell will finish dismantling the carbon skeleton of glucose entirely, stripping away its energetic electrons and releasing the leftover carbon as carbon dioxide — the very gas you breathe out with every exhalation.