Synthesis of Acetyl CoA

Question 1

What is the substrate for the TCA cycle?

Answer 1

Acetyl-CoA

Question 2

What enzyme links glycolysis with the TCA cycle by converting pyruvate to acetyl-CoA?

Answer 2

Pyruvate dehydrogenase

Question 3

True or false: Acetyl CoA can be converted back to pyruvate.

Answer 3

False

Question 4

What is most pyruvate converted to in resting muscle?

Answer 4

Acetyl-CoA

Question 5

What is most pyruvate converted to in very active muscle?

Answer 5

lactate

Question 6

True or false: Fatty acid degradation is an important source of acetyl Co-A.

Answer 6

True

Question 7

In which part of the cell does the TCA cycle take place?

Answer 7

Mitochondria

Question 8

What fate does the conversion of pyruvate to acetyl Co-A commit the carbon atoms of carbohydrates to?

Answer 8

Oxidation by the TCA cycle or to the synthesis of lipids.

Question 9

What moves pyruvate and H+ into the mitochondria after glycolysis?

Answer 9

Pyruvate-H+ symport

Question 10

True or false: The H+ from glycolysis is brought along with the pyruvate from glycolysis into the TCA cycle.

Answer 10

True

Question 11

True or false: The pyruvate dehydrogenase complex is large, made of five distinct enzymes, each with their own active site.

Answer 11

False; it is large and made of multiple copies of 3 distinct enzymes, each with their own active site.

Question 12

What three catalytic coenzymes are necessary for the pyruvate dehydrogenase reaction?

Answer 12

1) Thiamine pyrophosphate (TPP)
2) Lipoic acid
3) FAD

Question 13

What stoichiometric coenzymes are necessary for pyruvate dehydrogenase reaction?

Answer 13

1) CoA

2) NAD+

Question 14

Which coenzymes of pyruvate dehydrogenase function as substrates?

Answer 14

CoA and NAD+, the stoichiometric coenzymes

Question 15

Which coenzymes of pyruvate dehydrogenase function as catalysts and are not permanently altered by their participation in the reaction?

Answer 15

Thiamine pyrophosphate (TPP), Lipoic acid, and FAD

Question 16

What is the overall reaction catalyzed by pyruvate dehydrogenase complex?

Answer 16

pyruvate + CoA + NAD+&raquo_space;> acetyl-CoA + CO2 + NADH

Question 17

What regulates the activities of the pyruvate dehydrogenase complex?

Answer 17

Several kinases and phosphatases (it is under covalent modification control).

Question 18

What is the largest known multienzyme complex?

Answer 18

pyruvate dehydrogenase complex in the mitochondria

Question 19

Which enzyme in the pyruvate dehydrogenase complex requires TPP (thiamine pyrophosphate) to decarboxylate pyruvate?

Answer 19

Pyruvate dehydrogenase E1

Question 20

What are the three mechanistic steps of the conversion of pyruvate into acetyl CoA?

Answer 20

1) Decarboxylation
2) Oxidation
3) Transfer of the resulting acetyl group to CoA.

Question 21

Which is the function of the pyruvate decarboxylate E1 enzyme? What cofactor does it require?

Answer 21

Decarboxylation; TPP

Question 22

What are the three types of enzymes in the pyruvate dehydrogenase complex?

Answer 22

1) Pyruvate dehydrogenase E1
2) Dihydrolipoyl transacetylase E2
3) Dihydrolipoyl dehydrogenase E3

Question 23

What is the core of the pyruvate dehydrogenase complex formed from?

Answer 23

60 dihydrolipoyl transacetylase E2 trimers

Question 24

What is the core of E2 trimers surrounded by in the pyruvate dehydrogenase complex?

Answer 24

30 pyruvate dehydrogenase E1 alpha2beta2 heterotrimers

Question 25

What is the outer layer of the pyruvate dehydrogenase complex that holds the complex together?

Answer 25

12 E3 dimers and 12 or more E3 binding proteins that bind E3 to the E2 core.

Question 26

Where is the pyruvate dehydrogenase complex located?

Answer 26

In the mitochondria.

Question 27

What are the 5 cofactors required by pyruvate dehydrogenase?

Answer 27

1) Thiamine pyrophosphate (TPP
2) Lipoamide (lipoic acid)
3) CoA
4) FAD
5) NAD+

Question 28

What happens during the first reaction of pyruvate dehydrogenase?

Answer 28

E1 (with TPP) decarboxylates pyruvate (CO2 is lost).

Question 29

Which cofactor is required by the E2 enzyme in the second reaction of pyruvate dehydrogenase? How does it function?

Answer 29

Lipoamide (lipoic acid); functions as a swinging arm that moves intermediates (the disulfide group) from E1 to E3.

Question 30

What happens during the second reaction of pyruvate dehydrogenase?

Answer 30

The E2 converts the hydroxyethyl group made in E1 into an acetyl group.

Question 31

What happens during the third reaction of pyruvate dehydrogenase? What cofactor is required?

Answer 31

E2 catalyzes a transesterification reaction in which CoA is converted to acetyl CoA (with a high energy S-Carbonyl bond). CoA (cofactor) is required.

Question 32

What happens during the 4th reaction of pyruvate dehydrogenase?

Answer 32

Dihydrolipoyl dehydrogenase E3 regenerates E2’s lipoamide.

Question 33

What cofactor is required by E3 to regenerate E2’s lipoamide?

Answer 33

FAD

Question 34

What kind of reaction is the regeneration of E2’s lipoamide by E3?

Answer 34

A disulfide interchange reaction

Question 35

What happens during the 5th reaction of pyruvate dehydrogenase?

Answer 35

E3 is reoxidized by FAD funneling electrons to NAD+ to yield NADH.

Question 36

What cofactors are required to reoxidize E3?

Answer 36

FAD and NAD+

Question 37

Why is arsenic deadly for humans?

Answer 37

It interacts with the thionyl structures (it inhibits lipoamide) in pyruvate dehydrogenase, preventing the formation of acetyl CoA from pyruvate. This stops the TCA cycle from occurring, stopping the production of ATP.

Question 38

What deadly compound was once used as a treatment for syphilis because it is so much more toxic for bacteria than for humans?

Answer 38

Arsenic