Lecture 2 - TCA Cycle

Question 1

What is the main purpose of TCA cycle?

Answer 1

Produce energy!

Question 2

Where does TCA cycle occur?

Answer 2

• Mitochondria in eukaryotes

- Cytosol in prokaryotes

Question 3

Why does TCA cycle only work in one direction?

Answer 3

3 reactions have high negative delta G’s, making their pathways essentially irreversible

Question 4

Which 3 reactions of TCA cycle have high negative delta G’s?

Answer 4

1) Citrate synthase
2) Isocitrate dehydrogenase
3) Alpha-ketoglutarate dehydrogenase

Question 5

What 2 molecules are needed to make citrate?

Answer 5

Acetyl-CoA and oxaloacetate

Question 6

Which enzyme catalyzes the conversion of oxaloacetate to citrate and what type of reaction is this?

Answer 6

• Citrate synthase

- Condensation reaction

Question 7

What is the cofactor in the conversion of oxaloacetate to citrate?

Answer 7

H2O -> CoA-SH

Question 8

What inhibits citrate synthase?

Answer 8

Succinyl-CoA, ATP, and NADH

Question 9

What is the intermediate in the conversion of citrate to isocitrate?

Answer 9

Cis-aconitate

Question 10

Does aconitase work in one or both directions?

Answer 10

Both

Question 11

What are the cofactors in the conversion of citrate to isocitrate?

Answer 11

• H2O out

- H2O in

Question 12

What is the rate limiting step of TCA cycle?

Answer 12

Step 3, isocitrate dehydrogenase

Question 13

What is lost in the conversion of isocitrate to alpha-ketoglutarate?

Answer 13

CO2

Question 14

What type of reaction occurs for isocitrate to be converted to alpha-ketoglutarate?

Answer 14

Oxidative decarboxylation since NADH is formed (or NADPH if in cytosol)

Question 15

Isocitrate dehydrogenase is an ______ enzyme

Answer 15

Allosteric

Question 16

What activates isocitrate dehydrogenase?

Answer 16

ADP (low energy)

Question 17

What inhibits isocitrate dehydrogenase?

Answer 17

ATP and NADH (high energy)

Question 18

Which enzymes catalyzes the conversion of isocitrate to alpha-ketoglutarate?

Answer 18

Isocitrate dehydrogenase

Question 19

What are the cofactors in the conversion of isocitrate to alpha-ketoglutarate?

Answer 19

NAD+ -> NADH + H+ (will be NADP+ and NADPH if in cytosol)

Question 20

Alpha-ketoglutarate dehydrogenase has the same mechanism as _____

Answer 20

Pyruvate dehydrogenase

Question 21

What are the cofactors in the conversion of alpha-ketoglutarate to succinyl-CoA?

Answer 21

• TPP, FAD, and lipoic acid
• CoA-SH in
• NAD+ -> NADH

Question 22

Which enzymes catalyzes the conversion of alpha-ketoglutarate to succinyl-CoA?

Answer 22

Alpha-ketoglutarate dehydrogenase complex

Question 23

What inhibits alpha-ketoglutarate dehydrogenase?

Answer 23

NADH and succinyl-CoA

Question 24

Is the conversion of isocitrate to alpha-ketoglutarate reversible and why?

Answer 24

No because CO2 is released

Question 25

Is the conversion of alpha-ketoglutarate to succinyl-CoA reversible and why?

Answer 25

No because CO2 is released

Question 26

Which enzyme catalyzes the conversion of succinyl-CoA to succinate?

Answer 26

Succinyl-CoA synthetase

Question 27

What are the cofactors in the conversion of succinyl-CoA to succinate?

Answer 27

- GDP + Pi -> GTP | - CoA-SH out

Question 28

What type of reaction occurs for succinyl-CoA to be converted to succinate?

Answer 28

Substrate level phosphorylation

Question 29

Succinate is ____

Answer 29

Symmetrical

Question 30

Which enzyme catalyzes the conversion of succinate to fumarate?

Answer 30

Succinate dehydrogenase

Question 31

What are the cofactors in the conversion of succinate to fumarate?

Answer 31

FAD -> FADH2

Question 32

What is the delta G value of the conversion of succinate to fumarate?

Answer 32

0

Question 33

What is special about succinate dehydrogenase?

Answer 33

It is involved in the ETC

Question 34

Which enzyme catalyzes the conversion of fumarate to L-malate?

Answer 34

Fumarase

Question 35

What is the cofactor in the conversion of fumarate to L-malate?

Answer 35

H2O in

Question 36

Which enzyme catalyzes the conversion of L-malate to oxaloacetate?

Answer 36

Malate dehydrogenase

Question 37

What are the cofactors in the conversion of L-malate to oxaloacetate?

Answer 37

NAD+ -> NADH + H+

Question 38

What activates citrate synthase?

Answer 38

ADP

Question 39

What activates alpha-ketoglutarate dehydrogenase?

Answer 39

Ca2+