PDH

Question 0

3 stages of cellular respiration

Answer 0

1. Acetyl CoA synthesis
2. Citric Acid Cycle
3. electron transfer/oxidative phosphorylation

Question 1

Acetyl CoA

Answer 1

“receiving and shipping department” for all classes of biomolecules. A major source of metabolic energy.

Question 2

Input and output of the Pyruvate Dehydrogenase Complex

Answer 2

1 pyruvate = 1 Acetyl CoA, 1 CO2, and 1 NADH

THIS IS AN IRREVERSIBLE REACTION

Question 3

What are the 5 cofactors required by PDH?

Answer 3

1. TPP
2. Lipoic Acid
3. Coenzyme A
4. FAD (electron carrier)
5. NAD+ (electron carrier)

Question 4

Which functional group is considered to be the most important on the Coenzyme A molecule? Why?

Answer 4

The thiol group farthest from the ribonucleotide base. It is the functional group that binds to other carbons, making it the most important.

Adding an acetyl group to this thiol is what creates Acetyl CoA

Question 5

Which enzyme in the PDH does TPP permanently bind to?

Answer 5

E1 (pyruvate dehydrogenase)

Question 6

Which part of the TPP molecule is reactive? What does TPP do?

Answer 6

The thiazolium ring. It is a transient carbon carrier, binding briefly to a carbon group before transporting it to another molecule. It accepts the 2 carbon acetyl backbone after decarboxylation

Question 7

Which enzyme in the PDH is lipoic acid bound to?

Answer 7

E2 (dihydrolipoyl transacetylase)

Question 8

What are the names of the three enzymes found in the PDH complex?

Answer 8

E1 (pyruvate dehydrogenase), E2 (dihydrolipoyl transacetylase), and E3 (dihydrolipoyl dehydrogenase)

Question 9

Which part of lipoic acid is reactive? How many forms is it found in?
(lipoic acid is an 8 carbon chain)

Answer 9

The two thiol groups. They are observed in three forms:

1. Oxidized (ring structure)
2. Reduced (true thiol groups)
3. Acetylated (connected to the 2 carbon acetyl backbone)

Question 10

What are the functions of the three enzymes found in the PDH?

Answer 10

1. E1- oxidative decarboxylation of pyruvate
2. E2- transfer of acetyl group to CoA
3. E3- Regeneration of oxidized form of lipoic acid

Question 11

Which enzyme in the PDH is FAD bound to?

Answer 11

E3 (dihydrolipoyl dehydrogenase)

Question 12

What is the function of FAD in the PDH?

Answer 12

To take reduced lipoic acid and return it to its oxidized form. Removes the two hydrogens and then gives them to NAD+ to be removed as 1 molecule of NADH

Question 13

5 Reactions of the PDH

Answer 13

1. decarboxylation of pyruvate. Carbon dioxide leaves
2. lipoic acid arm moves to the active site of E1
3. transfer of acetyl group from TPP (E1) to lipoic acid (E2)
4. transfer of acetyl group from lipoic arm to CoA. Acetyl CoA leaves
5. regeneration of oxidized lipoic acid from reduced lipoic acid. NADH leaves

Question 14

examples of tightly-bound cofactor and loosely-bound cofactor

Answer 14

Tight- FADH2

Loose- NADH

Question 15

What is the advantage of having an enzyme complex over having three separate enzymes?

Answer 15

The proximity of the three enzymes speeds up the rate of reaction and increases the likelyhood of the reactions taking place at all.

Increases the overall reaction rate and minimizes side reactions

Question 16

Inhibitors of the PDH

Answer 16

High levels of NADH, ATP, and Acetyl CoA.

High levels = high energy = don’t need to waste energy making more

Question 17

Activators of the PDH

Answer 17

High levels of pyruvate and ADP

Question 18

PDH: active when phosphorylated or unphosphorylated?

Answer 18

Unphosphorylated. Phosphoryl group added by kinase, taken away by phosphatase.