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FM1030 Biochemistry > TCA cycle > Flashcards

TCA cycle Flashcards

1
Q

What are the 3 stages of the TCA cycle?

A

Acetyl CoA production
Acetyl CoA oxidation
Electron transfer and oxidative phosphorylation

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2
Q

Where in teh cell does the TCA cycle occur?

A

The matrix of the mitochondria

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3
Q

How is citrate formed?

A

Acetyl CoA joins with oxaloacetate to form citrate

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4
Q

How many redox reactions occur per turn of the cycle?

A

4

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5
Q

How many NADH molecules are produced per cycle?

A

3

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6
Q

How many FADH molecules are produced per cycle?

A

1

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7
Q

What are the functions of the TCA cycle?

A

Metabolism of all fuels
Participates in gluconeogenesis
Provides energy and metabolites for cell metabolism
Conversion of carbohydrates to fat
Source of non-essential amino acids (E&D)

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8
Q

What enters the TCA cycle?

A

Acetyl CoA

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9
Q

What is acetyl CoA the end product of?

A

Glycolysis
Beta-oxidation
Amino acid catabolism

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10
Q

What enzyme catalyses oxidative decarboxylation of pyruvate?

A

Pyruvate dehydrogenase

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11
Q

What does the oxidative decarboxylation of pyruvate form?

A

CoEnzyme A

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12
Q

What 5 coenzymes are needed for the oxidative decarboxylation of pyruvate?

A

TPP
Lipoyllysine
FAD
NAD
Acetyl CoA

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13
Q

What does Coenzyme A do?

A

Carries acyl groups and thioesters

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14
Q

What does high [ATP] mean?

A

Energy needs of the cell are being met

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15
Q

What does high [pyruvate] mean?

A

Cell requires energy

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16
Q

What steps of oxidative decarboxylation of pyruvate are regulated by enzyme 1?

A

Decarboxylated of pyruvate to an aldehyde
Oxidation of the aldehyde to a carboxylic acid

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17
Q

What steps of oxidative decarboxylation of pyruvate are regulated by enzyme 2?

A

Formation of acetyl CoA

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18
Q

What steps of oxidative decarboxylation of pyruvate are regulated by enzyme 3?

A

Reoxidation of lipoamide cofactor
Regeneration of the oxidised FAD cofactor - NADH produced

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19
Q

How is the condensation of oxaloacetate with acetyl CoA regulated?

A

Tightly, controlled step which is required for the cycle

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20
Q

What are the intermediates of the TCA cycle?

A

Citrate
Isocitrate
Alpha-ketoglutarate
Succinyl CoA
Succinate
Fumarate
L-Malate
Oxaloacetate

21
Q

What step(s) result in decarboxylation and NADH production?

A

Isocitrate to alpha-ketoglutarate
Alpha-ketoglutarate to succinyl CoA

22
Q

What happens during the conversion of succinyl CoA to succinate?

A

Substrate level phosphorylation forming GTP

23
Q

What step produces FADH2?

A

Succinate to fumarate

24
Q

What step results in ONLY the production of NADH?

A

L-malate to oxaloacetate

25
Q

What does high citrate concentrations mean?

A

Cell energy requirements are met

26
Q

What does the activity of the TCA cycle depend on?

A

Availability of NAD+ for the dehydrogenase reaction
Oxaloacetate and citrate concentrations
Pyruvate dehydrogenase activity
Citrate synthase activity
Isocitrate dehydrogenase activity
Alpha-ketoglutarate dehydrogenase activity

27
Q

What is the general regulatory mechanisms of the TCA cycle?

A

Activated by substrate availability
Inhibited by product accumulation
NADH and ATP inhibit
NAD+ and ADP activate

28
Q

What is the general regulatory mechanisms of the TCA cycle?

A

Activated by substrate availability
Inhibited by product accumulation
NADH and ATP inhibit
NAD+ and ADP activate

28
Q

What is the general regulatory mechanisms of the TCA cycle?

A

Activated by substrate availability
Inhibited by product accumulation
NADH and ATP inhibit
NAD+ and ADP activate

29
Q

What is needed for dehydrogenase reactions?

A

NAD+

30
Q

What does citrate synthase do?

A

Converts oxaloacetate and acetyl CoA to citrate

31
Q

What happens to citrate synthase during fasting?

A

[ATP] and [NADH] increase
Equilibrium between L-malate: oxaloacetate pushes towards L-malate
Malate is used for gluconeogenesis in cytosol
Acetyl CoA used for ketone synthesis due to lack of oxaloacetate

32
Q

What kind of enzymes regulate the TCA cycle and what are their names?

A

Exergonic
Citrate synthase
Isocitrate dehydrogenase
Alpha-ketoglutarate dehydrogenase

33
Q

What are the enzymes regulating the TCA cycle regulated by?

A

Energy indicators
Product accumulation
Substrate availability

34
Q

What downregulates pyruvate dehydrogenase?

A

Pyruvate dehydrogenase kinase

35
Q

What activates pyruvate dehydrogenase kinase?

A

Acetyl CoA
NADH

36
Q

What inactivates pyruvate dehydrogenase kinase?

A

Pyruvate
ADP
Ca++
K+

37
Q

What upregulates pyruvate dehydrogenase?

A

Pyruvate dehydrogenase phosphatase

38
Q

What activates pyruvate dehydrogenase phosphatase?

A

Ca++
Mg++

39
Q

Where is isocitrate dehydrogenase found in the cell?

A

Cytosol
Mitochondria

40
Q

What inhibits isocitrate dehydrogenase?

A

ATP & NADH

41
Q

What stimulates isocitrate dehydrogenase?

A

ADP, NAD+, Ca++

42
Q

How does isocitrate dehydrogenase behave in the absence of ADP?

A

Basically inactive

43
Q

What happens due to isocitrate dehydrogenase?

A

Decarboxylation
NADH production

44
Q

What stimulates alpha-ketoglutarate dehydrogenase?

A

Ca++

45
Q

What inhibits alpha-ketoglutarate dehydrogenase?

A

ATP
Succinyl CoA
NADH

46
Q

What occurs due to the activity of alpha-ketoglutarate dehydrogenase?

A

Decarboxylation
NADH produced

47
Q

How are 4 carbon intermediates formed?

A

Carboxylation of 3 carbon precursors

FM1030 Biochemistry (4 decks)

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