FINAL EXAM CHAPTER 18 Preparing for the cycle

Question 1

Where is the reaction occurring?

Answer 1

Inside the matrix of a mitochondria

Question 2

Under aerobic conditions what converts into Acetyl CoA and what is Acetyl CoA fuel for?

Answer 2

Pyruvate enters the mitochondria and converts into acetyl CoA

Acetyl CoA is the fuel for citric acid cycle

Question 3

What does the pyruvate dehydrogenase complex do?

Answer 3

It oxidatively carboxylates pyruvate to form acetyl CoA

Question 4

What are the three steps of the synthesis of acetyl CoA from pyruvate?

Answer 4

-decarboxylation
-oxidation
-transfer to CoA

Question 5

What is the enzyme name, prosthetic group of E1 and what reaction is being catalyzed?

Answer 5

-Pyruvate dehydrogenase component
-TTP(prosthetic group)

Reaction catalyzed:
-Oxidative decarboxylation of pyruvate

Question 6

What is the enzyme name , prosthetic group of E2 and what is the reaction being catalyzed?

Answer 6

-Dihydrolipoyl transacetylase
-Lipoamide

Reaction catalyzed:
Transfer of acetyl group to CoA

Question 7

What is the enzyme name, prosthetic group of E3 and what is the reaction being catalyzed?

Answer 7

-Dihydrolipoyl dehydrogenase
-FAD

Reaction catalyzed:
Regeneration of the oxidized form of lipoamide

Question 8

What happens at the decarboxylation step ?

Answer 8

=E1 catalyzes the decarboxylation. pyruvate combines with the ionized form of the coenzyme TPP

Question 9

What is a lipoamide?

Answer 9

A coenzyme that is formed by vitamin lipoic acid attaching to a lysine residue in E2

Question 10

What happens at the oxidation step?

Answer 10

The Hydroxyethyl group attached to TPP is oxidized to form an acetyl group while being simultaneously transferred to lipoamide.

Also the disulfide group of lipoamide is reduced to its disulfhydryl form in this reaction. The reaction is catalyzed by E1 and yields acetyl lipoamide

Question 11

What happens at the transfer/formation of acetyl CoA step?

Answer 11

-E2 catalyzes the transfer of the acetyl group from acetyl -lipoamide to coenzyme A to form acetyl CoA

Question 12

To participate in another reaction cycle what has to be done and what is this reaction catalyzed by?

Answer 12

Dihydrolipoamide must be oxidized
catalyzed by E3

Question 13

What is the flexible lipoamide arms role?

Answer 13

it allows for rapid movement of substrates and products from one active site of the complex to another

Question 14

What are the two principle fates of Acetyl CoA

Answer 14

-Metabolism by the citric acid cycle
-incorporation into fatty acids

Question 15

What molecules stimulate and inhibit the complex

Answer 15

inhibit:ATP,Acetyl CoA,NADH

stimulate:ADP ,pyruvate

Question 16

What does a kinase in the E1 do?

Answer 16

it goes through complex phosphorylates and inactivates E1.

Question 17

What does a phosphatase do in E1?

Answer 17

removes the phosphate and thereby activates the enzyme

Question 18

Where does the free energy get stored from the oxidation of pyruvate?

Answer 18

NADH and Acetyl CoA

Question 19

Why is the thioester bond high energy /unstable?

Answer 19

Its because sulfur is bigger than oxygen and this causes less delocalization of sulfur lone pairs toward carbonyl carbon