TCA Cycle and ETC

Question 1

Describe the TCA cycle

Answer 1

• cyclic pathway of 8 reactions
• cycle starts w/ condensation of acetyl coA and oxaloacetate and ends w/ regeneration of oxaloacetate
• no net production of any intermediates of the cycle
• 2 carbons enter as acetyl coA and leave as 2 CO2 molecules

Question 2

What is the importance of the TCA cycle?

Answer 2

• generation of NADH from NAD+
• removal of 2e- from intermediates
• intermediates are oxidized
• e- passed on to NAD+
• NADH now loaded w/ electrons it can use to make ATP (in the ETC)

Question 3

Describe the first reaction in the TCA cycle

Answer 3

catalyzed by citrate synthase to generate citrate from acetyl coA and oxaloacetate

Question 4

What is the rate-limiting step in the TCA cycle? What is it regulated by?

Answer 4

• the isocitrate dehydrogenase reaction
• inhibited by ATP and NADH
• stimulated by ADP and calcium

Question 5

alpha-ketoglutarate dehydrogenase

Answer 5

multi-enzyme complex that is analogous to pyruvate dehydrogenase

Question 6

Succinate thiokinase

Answer 6

involves substrate-level phosphorylation, producing GTP

Question 7

Succinate dehydrogenase

Answer 7

embedded in the inner mitochondrial membrane and is part of the ETC (oxidative phosphorylation)

Question 8

Fumarase

Answer 8

hydrates fumarate, converting it to malate

Question 9

Malate dehydrogenase

Answer 9

• catalyzes final reaction of TCA cycle

- uses NAD+ to convert malate to oxaloacetate and produces NADH+H as well

Question 10

What are the products of the TCA cycle?

Answer 10

• one molecule of GTP

- 4 electron pairs transferred during cycle, three pairs to NAD+ and one pair to FAD

Question 11

What are the three key points of regulation in the TCA cycle? Describe its activators and inhibitors:

Answer 11

• citrate synthase
• isocitrate dehydrogenase
• alpha-ketoglutarate dehydrogenase
• activators: ADP and Ca2+
• inhibitors: ATP, GTP, NADH, succinyl-coA