Krebs cycle

• Where does the link reaction occur in the cell?

  In the mitochondrial matrix
• What happens to pyruvate during the link reaction?

  It is decarboxylated and oxidized
• What role does coenzyme A play in the link reaction?

  It picks up the acetyl group
• What happens to NAD when it is reduced?

  It accepts hydrogens
• What is the process called when reduced NAD releases hydrogens?

  Oxidation
• What is the other coenzyme mentioned that is involved in the Krebs cycle?

  FAD
• How does FAD become reduced?

  By accepting hydrogen
• What is the first step in the Krebs cycle after acetyl CoA is introduced?

  Conversion of oxaloacetate into citrate
• What is the molecular structure of citrate?

  A six-carbon molecule
• What happens during the decarboxylation of citrate?

  Carbon dioxide is removed
• What is produced alongside the five-carbon molecule during the decarboxylation of citrate?

  Carbon dioxide and reduced NAD
• How many coenzymes are used during the conversion of the five-carbon molecule back to oxaloacetate?

  Three coenzymes
• What is substrate-level phosphorylation?

  The transfer of a phosphate from an intermediate molecule to produce ATP
• What is regenerated at the end of the Krebs cycle?

  Oxaloacetate
• How can you determine the number of decarboxylations needed for a molecule to enter the Krebs cycle?

  By looking at the number of carbons in the molecule
• What are the end products of glycolysis?

  Two reduced NADs and two net ATP molecules
• How many reduced NADs are produced from the Krebs cycle per glucose molecule?

  Six reduced NADs
• How many ATP molecules are produced from the Krebs cycle?

  Two ATP molecules
• What are the key steps in the Krebs cycle?

  1. Acetyl CoA combines with oxaloacetate to form citrate.
  2. Citrate undergoes decarboxylation to form a five-carbon molecule.
  3. Further decarboxylation and dehydrogenation occur.
  4. Substrate-level phosphorylation produces ATP.
  5. Regeneration of oxaloacetate occurs.
• What are the products of aerobic respiration from glycolysis, link reaction, and Krebs cycle?

  • Glycolysis: 2 reduced NADs, 2 net ATP
  • Link reaction: 2 reduced NADs
  • Krebs cycle: 6 reduced NADs, 2 reduced FADs, 2 ATP
• What should you focus on when answering questions about the Krebs cycle in exams?

  • Understand the number of decarboxylations and dehydrogenations.
  • Know the end products.
  • Be able to analyze intermediate stages based on carbon counts.
• Name the four-carbon compound which combines with acetyl in the Krebs cycle.


  Oxaloacetate
• What is the six-carbon compound formed in the first step of the Krebs cycle?


  Citrate
• What two chemical processes are involved in the conversion of the six-carbon compound into a five-carbon compound?

  Dehydrogenation and decarboxylation or oxidation and decarboxylation
• What is the process called after Link's reaction


  The Krebs cycle
• Which coenzymes act as hydrogen acceptors in the Krebs cycle?


  NAD and FAD