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Biochemistry II > Chapter 16 > Flashcards

Chapter 16 Flashcards

1
Q

What macromolecules are Acetyl CoA made of?

A

Carbohydrates or Fatty Acids

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2
Q

Where does the conversion of Pyruvate to Acetyl CoA happen?

A

Mitochondria

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3
Q

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

A

Pyruvate Dehydrogenase Complex

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4
Q

How does the Pyruvate Dehydrogenase Complex breakdown pyruvate?

A

Oxidative Decarboxylation

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5
Q

Look at the structure of Acetyl CoA

A

ADD

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6
Q

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

A

Thioester, covalent

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7
Q

Which vitamin does CoA come from?

A

B5

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8
Q

What three enzymes make up the Pyruvate Dehydrogenase Complex?

A

Pyruvate Dehydrogenase, Dihydrolipoyl Transacetylase and Dihydrolipoyl Dehydrogenase

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9
Q

What coenzymes do the Pyruvate Dehydrogenase Complex need?

A

TPP, FAD, NAD and lipoate

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10
Q

How does the Pyruvate Dehydrogenase Complex work?

A

(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.

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11
Q

Substrate Channeling

A

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

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12
Q

Citric Acid Cycle Reactions

A

Start with 1 Acetyl CoA

End with:

  • 2 CO2
  • 3 NADH
  • 1 FADH
  • 1 GTP or ATP
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13
Q

Citrate Synthase

A

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

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14
Q

Aconitase

A

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

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15
Q

Isocitrate Dehydrogenase

A

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

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16
Q

Alpha-Ketoglutarate Dehydrogenase Complex

A

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

17
Q

Succinyl-CoA Synthetase

A

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

18
Q

Nucleoside Diphosphate Kinase

A

Converts GTP to ATP.

19
Q

Succinate Dehydrogenase

A

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

20
Q

Fumarase

A

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

21
Q

Malate Dehydrogenase

A

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

22
Q

ATP From NADH or FADH2

A

NADH produces 2.5 ATP.

FADH2 produces 1.5 ATP.

23
Q

Citric Acid Cycle Feeding Pathways

A

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

24
Q

Pyruvate Dehydrogenase Complex Regulation

A

Negatively by:

  • Acetyl-CoA
  • NADH
  • ATP
  • Fatty Acids

Positively by:

  • low acetate
  • AMP
  • CoA
  • NAD+
25
Q

E1 Regulation

A

Inhibited by reversible protein phosphorylation.

26
Q

Exergonic Step Regulation

A

Citrate Synthase, Isocitrate Dehydrogenase and Alpha-Ketoglutarate Dehydrogenase Complex are allosterically regulated by the downstream products.

NADH inhibits all of the dehydrogenases

27
Q

Why can’t fatty acids be converted to carbohydrates?

A

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

28
Q

Feeding Citric Acid Cycle with Fatty Acids in Other Organisms

A

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

29
Q

Glyoxylate Cycle

A

Can convert Acetyl-CoA to succinate.

30
Q

Differences for Glyoxylate Cycle

A
  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.
31
Q

Fates of Oxaloacetate

A

Can be converted to PEP in gluconeogenesis

32
Q

Glyoxylate Cycle in Plants

A

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

33
Q

Which 3 Steps of the Citric Acid Cycle are irreversible?

A

Steps 1, 3 and 4

34
Q

Explain how substrate channeling works.

A

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

35
Q

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

A

Succinyl-CoA Synthetase

36
Q

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

A

Dehydrogenases

37
Q

Does the Glyoxylate Cycle happen in humans?

A

No

Biochemistry II (8 decks)

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