Metabolic Processes - Aerobic Cellular Respiration

Question 1

What is the difference between substrate-level phosphorylation and oxidative phosphorylation? (which produces more ATP)

Answer 1

• Substrate-level phosphorylation: an enzyme catalyzes a reaction between a substrate and an ADP (phosphate group from substrate is transferred to the ADP to produce ATP)
• Oxidative phosphorylation: NADH and FADH2 are oxidized to provide energy to phosphorylate ADP to make ATP (oxidation performed by ETC and phosphorylation performed by chemiosmosis)

Question 2

What happens during the energy investment stage of glycolysis?

Answer 2

1. Activation of glucose
2. Rearranging and phosphorylation
3. Cleavage of F-1,6-BP
   ** 2 ATP are used **

Question 3

What happens during the energy generation stage of glycolysis?

Answer 3

4. Oxidation and phosphorylation of G3P
5. ATP synthesis from BPG
6. Dehydration of 2PG
7. ATP synthesis from PEP
   ** 4 ATP produced per glucose molecule (2 ATP x2 because glucose is split in two) **

Question 4

What are the other sources of Acetyl-CoA and what happens if excess Acetyl-CoA is produced during pyruvate oxidation?

Answer 4

• Other sources: proteins, lipids, and carbohydrates can be converted to Acetyl-CoA (allows for their stored energy to be used in citric acid cycle and oxidative phosphorylation)
• Excess can be used to produce lipids to store energy as fat

Question 5

What is the role of oxaloacetate in the citric acid cycle?

Answer 5

• Oxaloacetate is a receptor molecule in the citric acid cycle
• It starts the series of reactions in the cycle an must be regenerated by the end to start the cycle again

Question 6

How is the free energy of electrons used by the electron transport chain? How does this differ when reduced by NADH vs FADH2?

Answer 6

• Free energy of the electrons is used pump H+ into the intermembrane space to create a concentration gradient
• This electrochemical gradient is used to phosphorylate ADP to ATP using ATP synthase
• NADH = 3 ATP produced
• FADH2 = 2 ATP produced

Question 7

Why do electrons move “down” the ETC? Why is oxygen required to keep electrons flowing?

Answer 7

• Each complex is slightly more electronegative than the last which pulls electrons from the complex before it
• If oxygen (one of the most electronegative elements) is not available, the ETC stops because electrons cannot be received so new electrons cannot enter

Question 8

What is the proton motive force and how is it produced?

Answer 8

• Proton motive force: a force that moves protons through an ATP synthase as a result of the free energy stored in the electrochemical gradient of protons across a biological membrane
• The electrochemical gradient is produced by the pumping of H+ into the intermembrane space

Question 9

How is the proton motive force is used to power chemiosmosis? What protein complex is needed for chemiosmosis to occur?

Answer 9

• Proton motive force pumps protons through ATP synthase which phosphorylates ADP to ATP
• ATP synthase is needed for chemiosmosis to occur