Kreb’s Cycle Worksheet
1. Krebs cycle occurs in the ______________________________________________________
2. The overall purpose of Krebs cycle is to __________________________________________
3. What product of private oxidation enters the cycle? _________________________________
4. What happens to the coenzyme A (CoA) that is released? ____________________________
5. Why is Krebs cycle also called the citric acid cycle? ________________________________
6. What makes the Krebs cycle cyclic? _____________________________________________
7. How many times does the cycle take place per molecule of glucose? ___________________
8. What happens to the two carbons that enter the cycle as acetyl-CoA? ___________________
9. At the end of the cycle, what is left of the original glucose molecule? ___________________
10. How many oxidations occur in one cycle? ______________
11. How many decarboxylations occur in one cycle? _______________
12. What is the number of NADH molecules yielded from each pyruvate? ____________ From each
glucose molecule? ____________
13. What is the number of FADH2 molecules yielded from each pyruvate? ____________ From each
glucose molecule? ____________
14. Why is FAD used instead of NAD+? ____________________________________________
15. What happens to these electron carriers after Krebs cycle? ___________________________
16. How many ATP are produced from each pyruvate? ____________ From each glucose molecule?
____________
17. What type of phosphorylation takes place to produce this ATP? _______________________
Kreb’s Cycle Worksheet
1. Krebs cycle occurs in the mitochondrial matrix
2. The overall purpose of Krebs cycle is to continue the oxidation of glucose and produce electron
carriers (NADH and FADH2). NADH and FADH2 carry the electrons and continue on to the
ETC. In the cycle, some energy is produced in the form of 2 molecules of ATP.
3. What product of private oxidation enters the cycle? The 2C Acetyl-CoA
4. What happens to the coenzyme A (CoA) that is released? It is recycled back into the cycle to
participate in pyruvate oxidation to pick up another acetyl group.
5. Why is Krebs cycle also called the citric acid cycle? First part of the cycle is the formation of
citric acid (citrate).
6. What makes the Krebs cycle cyclic? When 2C acetyl-CoA enters the cycle and reacts with 4C
oxaloacetate, it forms 6C citrate. Eventually, 6C citrate is transformed, through a series of
chemical reactions to regenerate 4C oxaloacetate. The 4C oxaloacetate will continue the cycle
with the addition of the 2C acetyl-CoA.
7. How many times does the cycle take place per molecule of glucose? Two (since one cycle involves
one pyruvate. 6C glucose was broken down into two 3C molecules of pyruvate).
8. What happens to the two carbons that enter the cycle as acetyl-CoA? The 2C acetyl-CoA reacts
with oxaloacetate to make 6C citrate.
9. At the end of the cycle, what is left of the original glucose molecule? Nothing. The original carbon
and oxygen atoms are in the form of CO2 and released as waste.
10. How many oxidations occur in one cycle? Four
11. How many decarboxylations occur in one cycle? Two
12. What is the number of NADH molecules yielded from each pyruvate? 3
From each glucose molecule? 6
13. What is the number of FADH2 molecules yielded from each pyruvate? 1
From each glucose molecule? 2
14. Why is FAD used instead of NAD+? At one step of Krebs cycle, succinate is oxidized to become
fumarate with the help of FAD. The energy involved succinate-fumarate reaction does not
allow NAD+ to be reduced sufficiently. FAD is lower-energy and is able to help oxidize
succinate in the process (and be reduced itself, picking up electrons).
15. What happens to these electron carriers after Krebs cycle? NADH and FADH2 continue on to the
electron transport chain to generate more ATP.
16. How many ATP are produced from each pyruvate? 1 From each glucose molecule? 2
17. What type of phosphorylation takes place to produce this ATP? Substrate-level phosphorylation