L4 - Pyruvate Dehydrogenase and TCA Cycle

Question 1

Thiamine deficiency leads to what complications?

Answer 1

1) Wernicke-Korsakoff syndrome

2) wet beri-beri

Question 2

What are the five enzymes of the pyruvate DHG complex?

Answer 2

1) pyruvate dehydrogenase
2) dihydrolipoyl dehydrogenase
3) dihydrolipoyl transacetylase
4) PDH kinase
5) PDH phosphatase

Question 3

What are the molecules which activate PDH?

Answer 3

1) insulin
2) catecholamines
3) pyruvate
4) calcium

Question 4

Where is the PDH complex found? Where does the TCA cycle occur?

Answer 4

PDH and TCA cycle occur in the mitochondrial matrix

Question 5

What are the sources of Acetyl CoA?

Answer 5

From glucose through glycolysis.

From fatty acids through beta oxidation. From conversion of BCAAs.

Question 6

Who are prone to thiamine deficiencies?

Answer 6

1) alcoholics

2) those with malnutrition

Question 7

What is the enzyme which converts alpha-ketoglutarate into succinyl coA? What are the cofactors?

Answer 7

alpha-ketoglutarate. uses CoASH and NAD+

Question 8

Phosphorylation of the PDH complex does what to the complex?

Answer 8

Inhibits it. Dephosphorylation will activate it.

Question 9

What are the four molecules into which pyruvate can be turned into? Which reactions are irreversible? Reversible?

Answer 9

1) alanine (reversible)
2) acetyl coA (irreversible)
3) oxaloacetate (irreversible)
4) lactate (reversible)

Question 10

How many NADH does the PDH complex make per pyruvate?

Answer 10

One NADH

Question 11

What are the four regulated enzymes of the TCA cycle?

Answer 11

1) citrate synthase
2) isocitrate DHG
3) alpha-ketoglutarate DHG
4) succinate DHG

Question 12

What are the molecules which inhibit PDH?

Answer 12

1) acetyl coA
2) ATP
3) NADH

Question 13

What are the four major mitochondrial myopathies?

Answer 13

1) LHON
2) Kearns-Sayre syndrome
3) MELAS syndrome
4) MERRF syndrome

Question 14

What are four functions of citrate?

Answer 14

1) source of cytosolic reducing equivalents
2) carbon source
3) regulator of metabolism
4) TCA cycle

Question 15

What is produced through the reaction of succinyl CoA into succinate? What is the enzyme that catalyzes this reaction and what is another name for it?

Answer 15

1) GTP and CoASH
2) succinyl CoA synthetase
3) succinate thiokinase

Question 16

Isocitrate is made from citrate through the actions of which enzyme?

Answer 16

Aconitase

Question 17

What is the equivalents in ATPs for NADH? for FADH2?

Answer 17

NADH = 3 ATP
FADH2 = 2 ATP

Question 18

How many ATP (net) per glucose molecule are made in the TCA cycle?

Answer 18

12 (3 NADH, 1 GTP, 1 FADH2)

Question 19

Which four intermediates of the TCA cycle can be made by conversion of amino acids?

Answer 19

1) oxaloacetate
2) fumarate
3) alpha-ketoglutarate
4) succinyl coA

Question 20

L-malate turns into oxaloacetate through the actions of which enzyme?

Answer 20

malate DHG

Question 21

Isocitrate DHG catalyzes a two-step reaction which turns what into what?

Answer 21

Isocitrate into alpha-ketoglutarate

Question 22

What are three clinical manifestations of PDH deficiency?

Answer 22

1) lactic acidosis
2) myopathy
3) neurological defects

Question 23

A high NADH/NAD+ implies which state? What happens with the TCA cycle?

Answer 23

1) implies high-energy state

2) inhibits TCA

Question 24

How is the inner mitochondrial membrane as compared to the outer mitochondrial membrane?

Answer 24

Much more impermeable to molecules

Question 25

What the main activators for enzymes in the TCA cycle? Main inhibitors?

Answer 25

Activators: ADP, calcium
Inhibitors: ATP, NADH, citrate

Question 26

Succinate is turned into fumarate via ______, which is turned into ______ by the actions of _______.

Answer 26

1) succinate DHG
2) L-malate
3) fumarase

Question 27

Which enzyme catalyzes the first proper step of the TCA cycle?

Answer 27

Citrate synthase

Question 28

What are the five coenzymes of the PDH complex?

Answer 28

1) lipoic acid
2) NAD+ (derived from vitamin B3/niacin)
3) FAD (derived from vitamin B2/riboflavin)
4) CoASH
5) thiamine pyrophosphate (TPP)

Question 29

Which molecule inhibits aconitase? Which one inhibits lipoic acid? Succinate dehydrogenase?

Answer 29

1) fluoroacetate inhibits aconitase
2) arsenic binds lipoic acid
3) malonate inhibits succinate DHG

Question 30

Which enzyme converts pyruvate into alanine? Into lactate? Into acetyl coA? Into oxaloacetate?

Answer 30

Alanine: alanine aminotransferase
Lactate: lactate dehydrogenase
Acetyl CoA: pyruvate dehydrogenase
Oxaloacetate: pyruvate carboxylase