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MBOD Week 10 > PDH and TCA cycle > Flashcards

PDH and TCA cycle Flashcards

1
Q

Does any type of substrate phosphorylation occur in the TCA cycle?

A

yes, one GTP is made

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2
Q

What is the overall goal of the TCA cycle?

A

Strip electrons from pyruvate and oxidize it completely to 3 CO2 molecules

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3
Q

How are electons recovered from the TCA cycle?

A

NADH an FADH2

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4
Q

How does the handling of pyruvate change as the cell moves from anaerobic to aerobic condition?

A

Anaerobic
- Pyruvate –> lactate

Aerobic
- Pyruvate –> 3 CO2

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5
Q

Where does the TCA cycle take place?

A
  • In the matrix of the mitochondria
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6
Q

T or F: all proteins involved in the TCA cycle are membrane bound.

A

False, the only membrane bound protein is succinate dehydrogenase

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7
Q

How does pyruvate get into the intermembrane space of the mitochondria and then into the matrix?

A
  • it passes through a porin in outer membrane

- uses carrier to get through the inner membrane

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8
Q

What 5 ways can the cell get Acetyl CoA?

A
  1. Glycolysis
  2. Amino Acid Oxidation
  3. Beta Oxidation
  4. Ethanol oxidation
  5. Ketone bodies
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9
Q

T or F: a mutation in the mitochondrial genome could prevent PDH complex transcription.

A

False, the PDH complex is coded for by the cell nucleus

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10
Q

What enzyme would be rendered dysfunctional if TPP its cofactor was removed?

A
  1. Subunit E1 of the PDH complex (aka pyruvate decarboxylase)
  2. Subunit E1 of alpha ketoglutarate dehydrogenase
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11
Q

Which subunit of PDH complex requires NAD+ and FAD?

A

Subunit E3

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12
Q

What is the cofactor for E2 in the PDH complex and what does it do?

A
  • Lipoic acid (contains oxidized disulfide bonds forming a 5 membered ring.
  • Reacts with carbanion intermediate created by E1 to make a thioester
  • Moves to E2 where the acetate is taken from the lipoic acid and a new thioester is formed with CoA (aka Acetyl-CoA)
  • Lipoic acid is released in reduced form (but must be reoxidized for cycle to continue)
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13
Q

T or F: the E3 subunit creates products that are used in the TCA cycle?

A

False, the job of the E3 subunit is to reoxidize the lipoic acid so that the E2 subunit can keep making acetyl CoA

  • Also, NADH is make from E3 which can be used in OxPhos
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14
Q

What is the first irreversible step in the TCA cycle, and what is the driving force for this reaction?

A
  • Condensation of OAA and Acetyl CoA to produce citrate
  • Catalyzed by Citrate Synthase
  • Hydrolysis of CoA drives the reaction
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15
Q

What does arsenite inhibit?

A

E2 of PDH

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16
Q

Describe the structural changes in citrate synthetase as well as the purpose of these changes.

A
  1. OAA binds, this opens up Acetyl-CoA binding site
  2. Acetyle-CoA binds
  3. Citroyl-CoA forms inducing another structural change that allows for hydrolysis

-The purpose of these steps is to protect against wasteful hydrolysis of acetyle-CoA

17
Q

Explain how acetyl CoA from the mitochondria can get to the cytosol.

A
  1. it must be converted citrate first by citrate synthase, because Acetyl-CoA has no mito. transporters
  2. Citrate can be exported from the mito.
  3. ATP citrate lyase cleaves citrate to making OAA and acetyl-CoA by adding CoA
18
Q

What two cycles are combined to make the TCA cycle and what is the linking enzyme between these two cycles?

A
  • 1st pt of TCA = alpha-ketoglutarate to make different amino acids
  • 2nd pt of TCA in backwards direction leads to succinyl CoA synthesis, used to make heme
  • alpha-ketoglutarate dehydrogenase is the linking enzyme
19
Q

T or F: alpha ketoglutarate dehydrogenase is related to the PDH complex.

A

True, The E1 and E2 subunits are extremely similar and the E3 subunit is exactly the same in both

20
Q

What enzymes in the TCA cycle are responsible for making NADH or FADH2?

A
  1. Isocitrate Dehydrogenase
  2. alpha-ketoglutarate dehydrogenase
  3. Succinate Dehydrogenase (FADH2)
  4. Malate Dehydrogenase
21
Q

What two enzymes are responsible for oxidative decarboxylation of citrate, aka release of CO2?

A
  1. Isocitrate Dehydrogenase

5. Alpha-ketoglutarate Dehydrogenase

22
Q

T or F: even if you have all TCA enzymes and lots of Acetyl CoA the cycle will not run unless a small amount of one of the intermediates is present.

A

True

23
Q

What prevents fats from being made into sugars?

A
  • The two oxidative decarboxylations in the TCA cycle
  • Two acetyl CoA carbons are added but two OAA carbons leave with each cycle leaving no carbons the can be used in biosynthesis
24
Q

What enzyme in the TCA cycle does substrate level phosphorylation?

A

Succinyl CoA synthetase makes GTP

25
Q

What pushes the malate dehydrogenase reaction forward despite its high activation energy?

A

OAA is constantly being removed by citrate synthase pulling the reaction forward

26
Q

What will happen in the TCA cycle after eating a large carb rich meal?

A
  • TCA will run until energy needs are met after this point TCA will be used for biosynthetic pathways to make amino acids from alpha ketoglutate, citrate will be exported to make fats, heme will be made from succinyl CoA.
27
Q

What is the most important reaction for filling up the TCA cycle if its depleted of OAA?

A
  • Pyruvate –> OAA by Pyruvate Carboxylase (PC)
  • PC recognizes depletion of TCA by high levels or acetyl CoA (which backs up when OAA is not available for 1st step of the TCA cycle)
28
Q

What happens when there is excess OAA in the TCA cycle?

A
  • PEPCK converts OAA –> PEP (USES 1 GTP)
  • PEP is then converted to pyruvate pyruvate kinase (PRODUCES 1 ATP)
  • Pyruvate can be turned into Acetyl-CoA

**Note: there is no net cost of energy for this reaction

29
Q

What are the major regulators of the PDH complex?

A

(-) ATP, Acetyl-CoA, NADH, Fatty Acids, phosphorylation

(+) AMP, CoA, NAD+, Ca2+, dephosphorylation

30
Q

What are the activators of the PDH kinase?

A

High ATP/ADP and NADH/NAD+ ratios and high acetyl CoA

31
Q

How is citrate key to determining a cells metabolic direction?

A
  1. Citrate is inhibitory to glycolysis

2. Citrate stimulates fatty acid biosynthesis

32
Q

What are the major regulators of Isocitrate dehydrogenase?

A

(-) NADH, Succinyl-CoA, citrate, ATP

(+) ADP

33
Q

What steps do yeast bypass in order to accomplish net synthesis from the TCA cycle?

A
  • decarboxylation steps
34
Q

What two enzymes are used in yeasts and bacteria to pass the two decarboxylation steps in the TCA cycle?

A
  1. Isocitrate lyase

2. malate synthase

MBOD Week 10 (5 decks)

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