Chapter 16

Question 1

What macromolecules are Acetyl CoA made of?

Answer 1

Carbohydrates or Fatty Acids

Question 2

Where does the conversion of Pyruvate to Acetyl CoA happen?

Answer 2

Mitochondria

Question 3

What is the enzyme that catalyzes the breakdown of Pyruvate to Acetyl CoA?

Answer 3

Pyruvate Dehydrogenase Complex

Question 4

How does the Pyruvate Dehydrogenase Complex breakdown pyruvate?

Answer 4

Oxidative Decarboxylation

Question 5

Look at the structure of Acetyl CoA

Answer 5

ADD

Question 6

What kind of linkage to CoA make to the acyl group?

Answer 6

Thioester, covalent

Question 7

Which vitamin does CoA come from?

Answer 7

B5

Question 8

What three enzymes make up the Pyruvate Dehydrogenase Complex?

Answer 8

Pyruvate Dehydrogenase, Dihydrolipoyl Transacetylase and Dihydrolipoyl Dehydrogenase

Question 9

What coenzymes do the Pyruvate Dehydrogenase Complex need?

Answer 9

TPP, FAD, NAD and lipoate

Question 10

How does the Pyruvate Dehydrogenase Complex work?

Answer 10

(1) Pyruvate is decarboxylated and the hydroxyethyl group is attached to TPP.
(2) The hydroxyethyl group is oxidized to make acetate covalently bonded to the lipoid group.
(3) The acetyl group is transesterified to CoA to make Acetyl-CoA.
(4) Hydrogen atoms on the lipoyl are transferred to FAD restoring the oxidized lipoyl group.
(5) FADH2 transfers the hydride to NAD+ forming NADH.

Question 11

Substrate Channeling

Answer 11

Found in PDC, intermediates never leave the complex. This helps maintain a high [substrate] and prevents other enzymes from using the acetyl group.

Question 12

Citric Acid Cycle Reactions

Answer 12

Start with 1 Acetyl CoA

End with:

• 2 CO2
• 3 NADH
• 1 FADH
• 1 GTP or ATP

Question 13

Citrate Synthase

Answer 13

Claisen condensation of the thioester and a ketone followed by hydrolysis with CoA to produce citrate. Irreversible.

Question 14

Aconitase

Answer 14

Goes through a cis-Aconitate intermediate to isocitrate. Isocitrate is used rapidly in the next reaction to favor a low mass action. Reversible.

Question 15

Isocitrate Dehydrogenase

Answer 15

Oxidative decarboxylation of isocirtate to form alpha ketoglurarate. Electrons are accepted by NAD to form NADH. CO2 is generated here. Irreversible.

Question 16

Alpha-Ketoglutarate Dehydrogenase Complex

Answer 16

Oxidative decarboxylation to form succinyl-CoA, forming NADH and CO2. Irreversible.

Question 17

Succinyl-CoA Synthetase

Answer 17

Hydrolysis of the thioester bond which drives the synthesis of ATP or GTP.

Question 18

Nucleoside Diphosphate Kinase

Answer 18

Converts GTP to ATP.

Question 19

Succinate Dehydrogenase

Answer 19

Oxidation of succinate to fumarate producing FADH2. Bound to the intermitochondrial membrane.

Question 20

Fumarase

Answer 20

Hydration of fumarate to L-malate. In reverse reaction only recognizes L-malate.

Question 21

Malate Dehydrogenase

Answer 21

Oxidation of L-malate to oxaloacetate producing NADH. Citrate Synthase uses up oxaloacetate to keep the mass action term low.

Question 22

ATP From NADH or FADH2

Answer 22

NADH produces 2.5 ATP.

FADH2 produces 1.5 ATP.

Question 23

Citric Acid Cycle Feeding Pathways

Answer 23

Can be feed by 4 and 5 carbon molecules as well. Some intermediates can be pulled put for other biosynthetic pathways.

Question 24

Pyruvate Dehydrogenase Complex Regulation

Answer 24

Negatively by:

• Acetyl-CoA
• NADH
• ATP
• Fatty Acids

Positively by:

• low acetate
• AMP
• CoA
• NAD+

Question 25

E1 Regulation

Answer 25

Inhibited by reversible protein phosphorylation.

Question 26

Exergonic Step Regulation

Answer 26

Citrate Synthase, Isocitrate Dehydrogenase and Alpha-Ketoglutarate Dehydrogenase Complex are allosterically regulated by the downstream products. NADH inhibits all of the dehydrogenases

Question 27

Why can't fatty acids be converted to carbohydrates?

Answer 27

PEP to pyruvate and pyruvate to acetyl CoA are to exergonic making them essentially irreversible

Question 28

Feeding Citric Acid Cycle with Fatty Acids in Other Organisms

Answer 28

Other organisms can convert fatty acids into succinate which is converted to oxaloacetate to feed gluconeogenesis.

Question 29

Glyoxylate Cycle

Answer 29

Can convert Acetyl-CoA to succinate.

Question 30

Differences for Glyoxylate Cycle

Answer 30

1. Isocitrate is cleaved by isocitrate lyase to succinate and glyoxylate. 2. Malate synthase condenses glyoxylate with a second molecule of acetyl-CoA to make malate.

Question 31

Fates of Oxaloacetate

Answer 31

Can be converted to PEP in gluconeogenesis

Question 32

Glyoxylate Cycle in Plants

Answer 32

Occurs primarily in lipid rich seeds. Done in the glyoxysomes.

Question 33

Which 3 Steps of the Citric Acid Cycle are irreversible?

Answer 33

Steps 1, 3 and 4

Question 34

Explain how substrate channeling works.

Answer 34

Holds onto the intermediates of multiple reactions so that they aren't used by unintended enzymes.

Question 35

Which enzyme in the Citric Acid Cycle produces GTP/ATP?

Answer 35

Succinyl-CoA Synthetase

Question 36

What class of enzymes always produces a product in the Citric Acid Cycle?

Answer 36

Dehydrogenases

Question 37

Does the Glyoxylate Cycle happen in humans?

Answer 37

No