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Bioenergetics > TCA cycle > Flashcards

TCA cycle Flashcards

1
Q

Metabolism (3)

A
  • the sum of all the chemical transformations
  • takes place in a cell or organism
  • occurs through a series of enzyme- catalyzed reactions
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2
Q

Catabolism

A

Degradative phase of metabolism in which organic molecules are converted into smaller, simpler end products

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3
Q

Catabolism

-characteristics (2)

A
  • release energy

- energy which is conserved in the formation of ATP and reduced electrons carriers (NADH, NADPH, FADH2)

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4
Q

Anabolic pathways

A

Small, simple precursors are bulit up into larger and more complex molecules (lipids, proteins)

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5
Q

Anabolism

-characteristics (1)

A

Require an input of energy, generally in the form of the phosphoryl group transfer potential of ATP and the reducing power of NADH, NADPH, FADH2

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6
Q

Anabolism and Catabolism

  • precursor molecules
  • end product
A

A: amino acids, sugars, fatty acid
C: carbohydrate, fats, proteins

A: proteins, lipids, nuclei acids
C: CO2, H2O, NH3

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7
Q

TCA cycle

  • substrate for this cycle
  • substrate is generated in
  • 2-carbon acetly group is…
  • energy is conserved as..
A
  • acetly CoA
  • the pathways for oxidation of fatty acids, glucose, amino acids
  • oxidized to two molecules of CO2
  • NADH, FADH2, GTP
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8
Q

TCA cycle

-function

A

-conserve the energy from the oxidation of acetyl CoA to CO2 by transferring electrons from intermediates of the cycle to NAD+ and FAD

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9
Q

TCA cycle

  • number of electrons donated by the acetyl group and what it forms
  • where does the cycle occur?
A

8 electrons donated –> 3 molecules of NADH and 1 of FAD

-mitochondria

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10
Q

Step 1-3

-only name and enzyme involved

A
  1. Formation of citrate/ Enzyme – citrate synthase
  2. Conversion of citrate to isocitrate/ Enzyme – acotynase
  3. Oxidation and decarboxylation of isocitrate/ Enzyme – isocitrate dehydrogenase
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11
Q

Step 4-6

-only name and enzyme involved

A
  1. Oxidative decarboxylation of a- ketoglutarate/ Enzyme – a- ketoglutarate dehydrogenase complex.
  2. Cleavage of succinyl CoA/ Enzyme – succinate thiokinase
  3. Oxidation of succinate/ Enzyme – succinate dehydrogenase
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12
Q

Step 7-8

-only name and enzyme involved

A
  1. Hydration of fumarate/ Enzyme – fumarase

8. Regeneration of oxaloacetate/ Enzyme – malate dehydrogenase

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13
Q

Energy produced by the TCA cycle (2)

A
  • Two carbon atoms enter the cycle as acetyl CoA and leave as CO2.
  • Four pairs of electrons are transferred during one turn of the cycle (3 reduce NAD+ to NADH, 1 reduce FAD to FADH2)
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14
Q

Oxidation of one NADH yields:

Oxidation of FADH2 yields:

A
  1. 5 ATP

1. 5 ATP

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15
Q

Total ATPs

A

10

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16
Q

Regulation of the TCA cycle

A

Regulated to correspond to the rate of the electron transport chain, which is regulated by the ATP/ADP ratio and the rate of ATP utilization.

17
Q

Regulation of the TCA cycle

-two major messengers

A
  • the phosphorylation state of ATP

- the reduction state of NAD+ (ratio NADH/NAD+).

18
Q

Regulation of Citrate Synthase

A
  • It has no allosteric regulators.

- Regulated by: concentration of citrate (=a product inhibitor).

19
Q

Regulation of Isocitrate Dehydrogenase

A
  • Is one of the rate-limiting steps.
  • Regulated allosterically: activated by ADP, Ca2+
  • inhibited by NADH.
20
Q

Regulation of α-ketoglutarate dehydrogenase

A
  • Inhibited by: NADH and succinyl CoA.

- Activated by Ca2+.

21
Q

Precursors of Acetyl CoA (3)

A
  • Compounds that enter as acetyl CoA are oxidized to CO2.
  • Compounds that enter the TCA cycle as acetyl CoA or as an intermediate that can be converted to malate or oxaloacetate
  • Compounds that enter as TCA cycle intermediates replenish intermediates that have been used but cannot be fully oxidized to CO2.
22
Q

Acetyl CoA

  • characteristics
  • it can be generated from…. (4)
A

-common point of convergence for the major pathways of fuel oxidation

  • the β-oxidation of fatty acids
  • degradation of the ketone bodies
  • Pyruvate is oxidized to acetyl CoA
  • amino acids, such as leucine and isoleucine are also oxidized to acetyl CoA
23
Q

Pyruvate

A

the end- product of aerobic glycolysis

24
Q

Pyruvate is oxidized to acetyl CoA by which complex?

A

the pyruvate dehydrogenase complex.

25
Q

Oxidative decarboxylation of pyruvate

A
  • must be transported into the mitochondria before it can enter the TCA cycle
  • a specific pyruvate transporter helps pyruvate across the inner mitochondrial membrane
  • Once in the matrix, pyruvate is converted to acetyl CoA
26
Q

Coenzymes of PDH

  • function
  • names - teresa leaves coccain filming nu
A
  • act as carriers or oxidants for the intermediates of the reactions
  • Thiamine pyrophosphate (TPP), Lipoic acid, CoA, FAD and NAD+.
27
Q

Deficiencies of thiamine or niacin

A
  • cause serious central nervous system problems

- because brain cells are unable to produce sufficient ATP (via the TCA cycle) if the PDH complex is inactive.

28
Q

Regulation of PDH

A
  • Phosphorylation by pyruvate dehydrogenase kinase, which inhibits the enzyme.
  • Dephosphorylation by pyruvate dehydrogenase phosphatase, which activates it.
29
Q

Regulation of PDH
-phosphorylation

-dephosphorylation

A
  • PDC kinase is inhibited by ADP and pyruvate.

- PDC phosphatase requires Ca2+ for full activity

30
Q

TCA cycle intermediates - thye are precursors for which pathways:

  • Citrate
  • a- ketoglutarate
  • Succinyl CoA
  • Malate
  • Oxaloacetate
A
  • fatty acid synthesis
  • amino acid synthesis
  • heme synthesis
  • gluconeogenesis
  • amino acid synthesis
31
Q

Anaplerotic Reactions

A
  • pathways or reactions that replenish the intermediates of the TCA cycle
  • Removal of any of the intermediates removes the 4 carbons that are used to regenerate oxaloacetate
32
Q

What happens if there is a depletion of oxaloacetate?

A

it is impossible to continue oxidizing acetyl CoA.

33
Q

Major anaplerotic enzyme, its function and how it is activated and inhibited

A
  • Pyruvate carboxylase
  • It catalyzes the addition of CO2 to pyruvate to form oxaloacetate
  • activated by acetyl CoA inhibited by high concentrations of many acyl CoA derivatives.
34
Q

How can ATP be generated?

A

It can be generated from oxidative phosphorylation when NADH and FADH2 donate these electrons to O2 via the electron transport chain

35
Q

Sources of Acetyl CoA (5)

A
  • fatty acid
  • ketone body
  • glucose
  • pyruvate
  • ethanol
36
Q

What is necessary to keep the TCA cycle running?

A

Cells have to supply enough 4C intermediates from degradation of carbohydrate or certain amino acids

37
Q

Majot anaplerotic pathways of the TCA cycle

-examples

A
  • carboxylation of pyruvate to oxalocetate
  • hydration of glutamate to α-ketoglutarate
  • β-oxidation of fatty acids to succinyl-CoA

Bioenergetics (4 decks)

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