Pyruvate Dehydrogenase and TCA: Theory Questions from Lecture Notes

Question 1

There are 2 ways that pyruvate can be metabolized: Explain them both briefly.

Answer 1

1. Anaerobic conditions: pyruvate can be converted into either lactate or ethanol
2. Aerobic conditions: pyruvate undergoes pyruvate dehydrogenase in order to be able to enter the TCA cycle

Question 2

Pyruvate is converted to _______ which heads to the TCA cycle

Answer 2

Acetyl CoA

Question 3

DNA —> mRNA

Answer 3

transcription

Question 4

mRNA —> enzyme

Answer 4

translation

Question 5

enzyme —> amino acid

Answer 5

turnover

Question 6

mRNA —> nucleotides

Answer 6

turnover

Question 7

Enzymes can undergo 4 different things: What are they?

Answer 7

1. Association with regulatory protein
2. Sequestration (compartmentation)
3. Allosteric regulation
4. Covalent modification

Question 8

What 2 things does the fate of pyruvate depend on?

Answer 8

1. presence/absence of O2

2. the type of organism

Question 9

How does pyruvate get converted into lactate?

Answer 9

Through muscle

Question 10

How does pyruvate get converted into ethanol?

Answer 10

Through yeast (production of ethanol releases CO2)

Question 11

What enzyme converts pyruvate to lactate?

Answer 11

Lactate dehydrogenase

Question 12

What are the cofactors when pyruvate is converted into lactate?

Answer 12

NADH + H+ —> NAD+

Question 13

Describe the anaerobic metabolism of pyruvate in the muscle (lactate is being produced)

Answer 13

When available O2 is low, it is necessary to reoxidize NADH to NAD+ to keep glycolysis going.

The delta G is negative.

This occurs in skeletal muscle.

Lactate converted back to pyruvate in other tissues with high O2 (heart).

Question 14

Describe Fermentation, the anaerobic metabolism of pyruvate in yeast (ethanol is being produced)

Answer 14

This has been exploited by the brewing industry to produce ethanol for beer, wine, or even to fuel cars

Yeast start using up the O2 in the medium but once it runs out they switch to fermentation

CO2 is released during process

NAD+ is produced to allow glycolysis to proceed

Question 15

What enzyme converts pyruvate to acetaldehyde? (irreversible)

Answer 15

pyruvate decarboxylase

Question 16

What are the cofactors when pyruvate is converted to acetaldehyde?

Answer 16

CO2 is lost

Question 17

What enzyme converts acetaldehyde to ethanol? (reversible)

Answer 17

alcohol dehydrogenase

Question 18

What are the cofactors when acetaldehyde is converted to ethanol?

Answer 18

NADH + H+ —-> NAD+

Question 19

When alcohol is metabolized what is the toxic byproduct?

Answer 19

acetaldehyde (this is responsible for the hangover)

*Ethanol is metabolized in the liver that is why alcoholics have liver problems.

Question 20

What is the process called when pyruvate is aerobically metabolized ?

Answer 20

Pyruvate dehydrogenase

Question 21

What 3 major enzymes are a part of PDH?

Answer 21

E1: pyruvate decarboxylase (uses ATP)
E2: dihydrolipoate transacetylase (uses lipoic acid)
E3: dihydrolipoate dehydrogenase (NADH-FADH2 oxidoreductase)

Question 22

Briefly explain the process of PDH

Answer 22

When oxygen levels are normal, oxidative phosphorylation can occur to produce NAD+ and pyruvate is metabolized more completely to produce NADH.

The NADH that is produced is then reoxidizes via the ETC (irreversible reaction).

Question 23

Where does PDH occur in eukaryotes and bacteria?

Answer 23

Eukaryotes: mitochondria
Bacteria: cytosol

Question 24

List some of the cofactors involved in PDH

Answer 24

FAD in E3
NAD
Lipoic acid in E2
TPP in E1
CoA

Question 25

What vitamins are required for PDH?

Answer 25

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

Question 26

Describe the PDH complex

Answer 26

-large complex
-12 subunits
-5X as big as one ribosome and can be seen with a microscope
When P is present, it is inactive
When P is not present, it is active

See slide 20

Question 27

You can only enter TCA as ______

Answer 27

Acetyl CoA

Question 28

You can only leave TCA as _______

Answer 28

CO2