Chapter 18: Preparation for the Cycle

Question 1

Under _____ conditions, pyruvate enters the mitochondria and is converted to ________.

Answer 1

Aerobic conditions

Acetyl CoA

Question 2

Acetyl CoA is the fuel for the…

Answer 2

Citric acid cycle

Question 3

Oxidative decarboxylation of pyruvate and the reactions of the citric acid cycle occur within…

Answer 3

The mitochondrial matrix

Question 4

Pyruvate translocase transports the pyruvate produced during glycolysis in the _______ into __________ in ____________.

Answer 4

Cytoplasm to mitochondria

In symport with H+

Question 5

Pyruvate dehydrogenase complex catalyzes the oxidative phosphorylation of _______ to _______.

Answer 5

Pyruvate to acetyl CoA

Question 6

Pyruvate dehydrogenase complex is ________ and a link between…

Answer 6

Irreversible reaction

Link between glycolysis and the citric acid cycle

Question 7

PDH requires 3 enzymes to synthesize acetyl CoA. What are they?

Answer 7

1. Pyruvate dehydrogenase component (E1)
2. Dihydrolipoyl transacetylase (E2)
3. Dihydrolipoyl dehydrogenase (E3)

Question 8

The prosthetic group for E1 is…

Answer 8

TPP

Question 9

The prosthetic group for E2 is…

Answer 9

Lipoamide

Question 10

The prosthetic group for E3 is…

Answer 10

FAD

Question 11

3 steps of PDH are…

Answer 11

1. Decarboxylation
2. Oxidation
3. Transfer to CoA

Question 12

What is the catalyst for the decarboxylation reaction?

Answer 12

E1 or pyruvate dehydrogenase component

*Combines with TPP

Question 13

Step 2 of PDH:

Answer 13

Oxidation of TPP by E1

Question 14

Step 3 of PDH:

Answer 14

Formation of acetyl CoA (E2) + dihydrolipoamide (reduced form)

Question 15

Step 4 of PDH:

Answer 15

Dihydrolipoamide is oxidized back to lipoamide (E3)

Question 16

What two conditions must be present for the coordinated catalysis of this reaction?

Answer 16

1. Flexible lipoamide arm
2. Structural integration of the 3 enzymes (must be tightly associated)

Question 17

What happens if lipoamide or TPP are not present?

Answer 17

Pyruvate will not convert to Acetyl CoA

Question 18

Acetyl CoA has two key principle fates:

Answer 18

1. Metabolism by the citric acid cycle
2. Incorporation into fatty acids

Question 19

Because it is an irreversible reaction, acetyl CoA cannot convert back to ______ and therefore _____ cannot be used to make _____.

Answer 19

Glucose

Lipids cannot form glucose from acetyl CoA

Question 20

PDH is regulated by _________ and _________.

Answer 20

Covalent modification and allosteric interactions

Question 21

A kinase associated with the complex __________ and __________ E1 subunit of PDH.

Answer 21

Phosphorylates and inactivates E1

Question 22

A phosphatase associated with the complex removes the _______ and thereby _______ the enzyme.

Answer 22

Removes phosphate

Activates the enzyme

Question 23

PDH also regulated by allosteric reactions, specifically…

Answer 23

Energy charge

Question 24

PDH is inhibited by…

Answer 24

• ATP
• Acetyl CoA
• NADH

Question 25

PDH activated by...

Answer 25

* ADP * Pyruvate

Question 26

If there is a phosphotase deficiency, PDH is always ________ and therefore \_\_\_\_\_\_.

Answer 26

Phosphorylated; inactive

Question 27

When inactive, PDH is converted to ______ leading to __________ and malfunctioning the \_\_\_\_\_\_\_\_\_\_\_\_.

Answer 27

Converted to lactate Leading to **lactic acidosis ** Malfunctioning CNS

Question 28

Beriberi: A neurological and cardiovascular disorder caused by dietary deficiency of _______ or \_\_\_\_\_\_.

Answer 28

Thiamine or vitamin B1

Question 29

With Beriberi, PDH activity is _____ and results in...

Answer 29

Activity is low Results in pyruvate accumulation. No conversion to acetyl CoA? This limits ATP production!

Question 30

What causes similar symptoms to those in Beriberi?

Answer 30

Exposure to mercury or arsenite

Question 31

Arsenite and mercury bind to _________ and ______ PDH complex.

Answer 31

Bind to dihydrolipoamide Inhibit PDH

Question 32

What relieves the inhibition of PDH by forming a complex with arsenite?

Answer 32

Sulfhydryl reagents

Question 33

What is the arsenic-based chemical weapon used in WWI?

Answer 33

Lewisite

Question 34

The prosthetic group _____________ is required for the transfer of the acetyl group to coenzyme A.

Answer 34

Lipoamide

Question 35

The Pyruvate Dehydrogenase (PDH) Complex is allosterically activated by high levels of:

Answer 35

Pyruvate

Question 36

The E2 enzyme (dihydrolipolyl transacetylase) of the pyruvate dehydrogenase complex contains _______________ as prosthetic group and catalyzes the\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.

Answer 36

Lipoamide; transfer of the acetyl group to CoA.

Question 37

How does the antidote for lewisite work?

Answer 37

BAL: Sulfhydryl reagent 2,3-dimercaptopropanol reacts arsenite and is then excreted