Lecture 2 - Fate of Pyruvate

Question 1

What determines the fate of pyruvate?

Answer 1

• Presence/absence of oxygen

- Type of organism

Question 2

What can pyruvate be converted into?

Answer 2

• Ethanol
• Lactate
• Acetyl-CoA

Question 3

Where is pyruvate converted into lactate?

Answer 3

Muscle

Question 4

What converts pyruvate into ethanol?

Answer 4

Yeast

Question 5

Why is pyruvate anaerobically metabolized?

Answer 5

To reoxidize NADH to NAD+ to keep glycolysis going

Question 6

Where and under what conditions is lactate converted to pyruvate?

Answer 6

• In the heart

- During high oxygen periods

Question 7

What is released during fermentation?

Answer 7

CO2

Question 8

Which enzyme converts pyruvate to lactate?

Answer 8

Lactate dehydrogenase

Question 9

Which enzyme converts lactate to pyruvate?

Answer 9

Lactate dehydrogenase

Question 10

What is the cofactor in the conversion of pyruvate to lactate?

Answer 10

NADH + H+ -> NAD+

Question 11

Which enzyme converts pyruvate to acetaldehyde?

Answer 11

Pyruvate decarboxylase

Question 12

Which enzyme converts acetaldehyde to ethanol?

Answer 12

Alcohol dehydrogenase

Question 13

Which enzyme converts ethanol to acetaldehyde?

Answer 13

Alcohol dehydrogenase

Question 14

What is the cofactor in the conversion of pyruvate to acetaldehyde?

Answer 14

CO2 lost

Question 15

What is the cofactor in the conversion of acetaldehyde to ethanol?

Answer 15

NADH + H+ -> NAD+

Question 16

_____ accumulation causes a hangover

Answer 16

Acetaldehyde

Question 17

Which enzyme converts acetaldehyde to acetate?

Answer 17

Acetaldehyde dehydrogenase

Question 18

What is the cofactor in the conversion of acetaldehyde to acetate?

Answer 18

NAD+ -> NADH + H+

Question 19

Where does the conversion of acetaldehyde to acetate occur?

Answer 19

In the liver

Question 20

Which enzymes catalyzes the conversion of acetate to acetyl CoA?

Answer 20

Acetyl-CoA synthetase

Question 21

What is the cofactor in the conversion of acetate to acetyl-CoA?

Answer 21

ATP -> AMP + PPi

Question 22

How many ATP molecules can be produced from one ethanol molecule? Describe where each is produced/used

Answer 22

• 2 NADH produced from the conversions of ethanol and acetaldehyde, which is equivalent to 5 ATP
• 2 ATP used for the production of acetyl-CoA
• Total of 3 ATP produced

Question 23

How can you physically tell that someone has acetaldehyde accumulation?

Answer 23

Red cheeks

Question 24

Which enzyme catalyzes the conversion of pyruvate to acetyl-CoA?

Answer 24

Pyruvate dehydrogenase complex

Question 25

What are the cofactors in the conversion of pyruvate to acetyl-CoA?

Answer 25

- CoA-SH in - NAD+ -> NADH - TPP, lipoate, FAD

Question 26

What are the 3 enzymes that make up pyruvate dehydrogenase?

Answer 26

1) Pyruvate decarboxylase 2) Dihydrolipoate transacetylase 3) Dihydrolipoate dehydrogenase

Question 27

What does pyruvate decarboxylase use?

Answer 27

TPP

Question 28

What does dihydrolipoate transacetylase use?

Answer 28

Lipoic acid

Question 29

What is the function of dihydrolipoate dehydrogenase?

Answer 29

NADH-FADH2 oxidoreductase

Question 30

Which vitamins are required for pyruvate dehydrogenase and why?

Answer 30

- Riboflavin (B2) for FAD - Niacin (B3) for NAD - Panthothenate (B5) for CoA - Thiamine (B1) for TPP

Question 31

Where does the conversion of pyruvate to acetyl-CoA occur?

Answer 31

- Mitochondria in eukaryotes | - Cytosol in bacteria

Question 32

How can pyruvate dehydrogenase be inactivated?

Answer 32

NADH (a high energy signal) activates protein kinase, which converts pyruvate dehydrogenase to an inactive form

Question 33

How many subunits does pyruvate dehydrogenase have?

Answer 33

12

Question 34

How can pyruvate dehydrogenase be activated?

Answer 34

By protein phosphatase

Question 35

What are the cofactors required for pyruvate dehydrogenase and in which complex do they work?

Answer 35

1) Thiamine pyrophosphate (TPP) in E1 2) Lipoic acid in E2 3) Flavian adenine dinucleotide (FAD) in E3 4) NAD and CoA

Question 36

What is NAD short for?

Answer 36

Nicotinaminde adenine dinucleotide

Question 37

What is the active portion of TPP called?

Answer 37

Thiazolium ring

Question 38

Where is a thiazolium ring found besides TPP?

Answer 38

- Alpha-ketoglutarate dehydrogenase | - Isovalerate dehydrogenase

Question 39

What does lipoate act as?

Answer 39

An acyl carrier and an electron carrier

Question 40

What is the first step of pyruvate dehydrogenase and what can be the attacker in this step?

Answer 40

- The attack of the TPP carbanion, followed by the release of CO2 - Either pyruvate dehydrogenase or pyruvate decarboxylase

Question 41

Where is pyruvate dehydrogenase used?

Answer 41

In mitochondria

Question 42

Where is pyruvate decarboxylase used?

Answer 42

Yeast fermentation

Question 43

What is the product of the first step of pyruvate dehydrogenase?

Answer 43

- Acetaldehyde if the attacker is pyruvate decarboxylase | - Acetyl-CoA if the attacker is pyruvate dehydrogenase

Question 44

How is lipoic acid converted back to its original form in pyruvate dehydrogenase?

Answer 44

FAD and NAD+ (eventually) act as electron acceptors

Question 45

What would happen to pyruvate dehydrogenase if lipoic acid wasn't present?

Answer 45

Acetaldehyde would be produced

Question 46

Does the pyruvate dehydrogenase or pyruvate decarboxylase reaction use TPP?

Answer 46

Both

Question 47

What happens in the second step of the pyruvate dehydrogenase mechanism?

Answer 47

Transfer of 2 electrons and acetyl group to lipoate

Question 48

What happens in the third step of the pyruvate dehydrogenase mechanism?

Answer 48

Transesterification

Question 49

What happens in the fourth step of the pyruvate dehydrogenase mechanism?

Answer 49

2 electrons are transferred to FAD from dihydrolipoate (E3)

Question 50

What happens in the fifth step of the pyruvate dehydrogenase mechanism?

Answer 50

Oxidation of FADH2 from E3 by NAD+