1. Lecture packet 6 Reading: Chapter 3 (pages 56-62)
Cellular Metabolism
Lecture packet 6
Reading: Chapter 3 (pages 56-62)

2. Outline
▪ Glycolysis
▪ Citric Acid Cycle
▪ Electron transport chain

3. Metabolism
▪ Metabolism consists of all the chemical reactions that take place in a cell.
▪ Aerobic cellular respiration requires oxygen and produces carbon dioxide.
▪ Anaerobic fermentation does not require oxygen.

4. Why is aerobic respiration so important?

5. Aerobic respiration ▪ There are four steps of aerobic respiration:
Glycolysis
Transition reaction
Citric Acid cycle (Krebs cycle)
Electron transport chain

6. Glycolysis ▪ Phase 1: Glycolysis ▪ It occurs in the cytoplasm.
▪ Splits one glucose into two pyruvate molecules.
▪ Generates a net gain of 2 ATP and 2 NADH molecules.
▪ Does not require energy.

7. Glycolysis

8. Glycolysis ▪ The starting material is glucose.
▪ It ends with 2 ATP, 2 NADH, and 2 pyruvate molecules.

9. Glycolysis
▪ Know what goes in and what goes out!

10. Transition reaction ▪ Phase 2: Transition reaction
▪ It occurs within the mitochondria.
▪ Coenzyme A combines with pyruvate to form acetyl CoA and CO2.
▪ Forms 2 Acetyl CoA molecules and 2 NADH and 2 CO2.

11. Transition reaction ▪ Starts with:
- 2 Pyruvate molecules (3 carbon molecules)
- 2 Coenzyme A
▪ Ends with:
- 2 CO2
- 2 NADH
- 2 Acetyl CoA (2 carbon molecules)

12. Transition reaction

13. Citric Acid cycle (Krebs cycle)
▪ Phase 3: Citric acid cycle
▪ Occurs in the mitochondria
▪ Acetyl CoA enters the citric acid cycle
▪ Releases 2 ATP, 4 CO2, 2 FADH2, and 6 NADH
▪ Requires oxygen, but doesn’t use oxygen.

14. Citric Acid cycle (Krebs cycle)
▪ Starts with:
- 2 Acetyl CoA molecules
▪ Ends with:
- 2 ATP
- 4 CO2
- 2 FADH2
- 6 NADH

15. Electron transport chain
▪ Phase 4: Electron transport chain
▪ Electrons of FADH2 and NADH are transferred from one protein to another until they reach oxygen, the ultimate electron acceptor.
▪ Releases energy that results in 32 ATP.
▪ Requires oxygen.
Typically, 3 ATP per NADH and 2 ATP per FADH2

16. Electron transport chain: electron carriers and acceptor
▪ NADH and FADH2 are important carriers of electrons.
▪ They donate electrons to the electron transport chain.
▪ At the end of the chain, oxygen accepts the electrons.

17. Electron transport chain
▪ When electrons go from one protein to another, it loses energy, which is lost as heat and also allows the membrane complexes I, III, and IV to pump protons from the matrix to the intermembrane space.
▪ This creates a gradient that allows protons to go back through complex V, ATP Synthase, and this is what ultimately produces energy.

18. Electron transport chain

19. Electron transport chain

20. How ATP is made using the ETC
In the mitochondria, the NADH and FADH2 donate electrons to the electron transport chain.
Oxygen is the final electron acceptor from the ETC.
The ETC uses the energy from the electrons to transport protons (H+) against the concentration gradient (matrix to the intermembrane space of the mitochondria).

21. How ATP is made using the ETC
4. The ATP synthase transports the hydrogen ions back to the lumen of the mitochondria.
5. The hydrogen ions go through the ATP synthase, and this movement provides energy to catalyze the reaction of ADP + Pi  ATP.

22. Summary of cellular respiration
▪ One molecule of glucose is broken down and 36 ATP molecules are generated.
▪ Oxygen is used by the electron transport chain

23. Summary of cellular respiration (aerobic)
▪ Glycolysis starts the process in the cytoplasm by breaking apart the glucose molecule. It produces 2 ATP, 2 NADH, and 2 pyruvate molecules.
▪ Next, it goes to the mitochondria to undergo the transition reaction, which produces 2 CO2, 2 NADH, and 2 Acetyl CoA molecules.
▪ And then the 2 Acetyl CoA molecules go into the citric acid cycle to produce 2 ATP, 4 CO2, 2 FADH2, and 6 NADH.

24. Summary of cellular respiration (aerobic)
▪ Finally, the electron donors pass the electrons through a series of proteins. Some of the proteins pump hydrogen ions from the matric into the intermembrane space. And then the hydrogen ions flow back down the concentration gradient through ATP synthase, and this in turn produces ATP.
▪ One glucose can produce a total of 36 ATP.

25. Summary of cellular respiration

26. Not just glucose!
▪ Other molecules can undergo energy production. They just enter at different stages of cellular respiration.

27. Anaerobic respiration
▪ Sometimes organisms, including humans, need to produce energy without using oxygen.
▪ When you need energy quick (such as during exercise), or if there is not enough oxygen, then the cell will still undergo glycolysis. But it won’t undergo the other steps of aerobic cellular respiration (Citric Acid cycle and ETC).

28. Anaerobic respiration: fermentation
▪ Breakdown of glucose without oxygen.
▪ Takes place entirely in the cytoplasm.
▪ It is very inefficient, resulting in only two ATP.

29. Anaerobic respiration: fermentation
▪ When cells need energy quick, they will use this pathway for a short time.
▪ 2 pyruvic acid + 2 NADH  2 lactate + 2 NAD+
▪ End result is lactate and NAD+, in addition to the 2 ATP produced from glycolysis.

30. Anaerobic respiration: fermentation

31. What is the starting molecule of glycolysis?
Acetyl CoA
Protein
Glucose
Pyruvate

32. Which stage produces carbon dioxide?
Glycolysis
Electron transport chain
Transition reaction
Citric acid cycle
Both 3 and 4

33. Which stage uses oxygen?
Glycolysis
Krebs cycle
Electron transport chain

34. Which stage produces the most NADH
Glycolysis
Krebs cycle
Electron transport chain

35. Which stage produces the most ATP
Glycolysis
Krebs cycle
Electron transport chain