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SfM topics > Carbohydrates 5: Citric Acid Cycle > Flashcards

Carbohydrates 5: Citric Acid Cycle Flashcards

1
Q

where does citric acid cycle occur?

A

mitochondrial matrix

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2
Q

what are 3 common “fuel” molecules?

A
  • carbohydrates
  • amino acids
  • fatty acids
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3
Q

does the cycle produce ATP directly?

A

No

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4
Q

does the cycle include O2 as the reactant directly?

A

No

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5
Q

As electrons are formed, what two reduced electron carriers are produced?

A

NADH and FADH2

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6
Q

In which glycolysis step is the NAD converted to NADH ( reduction)

A

step 6

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7
Q

in which step in glycolysis is NADH re-oxidised? (to form NAD again)

A

Pyruvate to lactate step

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8
Q

what is citric acid cycle in simple words?

A

Stripping molecules from their electrons which are carried to terminal respiration step. Electrons are harvested to completely oxidise food molecules to CO2, H2O and make lots of energy

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9
Q

what 2 substances can be oxidised to form acetyl CoA?

A
  1. pyruvate (from glycolysis)

2. fatty acids

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10
Q

what enzyme is used to break down pyruvate into acetyl CoA?

A

pyruvate dehydrogenase

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11
Q

what 3 steps/ series of reactions occur when acetyl CoA is formed from pyruvate?

A
  1. decarboxylation of pyruvate
  2. oxidation
  3. transfer/attachment of CoA complex
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12
Q

what does the carboxylation step in formation of acetyl CoA from pyruvate release?

A

2 electrons (2H ions)

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13
Q

what electron carrier goes through reduction in the formation of acetyl CoA from pyruvate?

A

NAD turns to NADH (carries the 2 electrons released through pyruvate dehydrogenase)

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14
Q

what is pyruvate dehydrogenase made up of?

A

Many copies of each enzyme subunit

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15
Q

what is the advantage of having several enzyme subunits making up pyruvate dehydrogenase?

A

each subunit catalyses a different part of the reaction

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16
Q

what does E1 subunit in pyruvate dehydrogenase catalyse?

A

first decarboxylation of pyruvate

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17
Q

what does E2 subunit in pyruvate dehydrogenase catalyse?

A

transfers the acetyl group to coenzyme A

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18
Q

what does the E3 subunit in pyruvate dehydrogenase catalyse?

A

recycles lipoyllysine through reduction of FAD which is recycled by passing electrons to NAD+

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19
Q

why is CAC called the “black box”?

A

because intermediate molecules that make up the cycle remain CONSTANT at all times

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20
Q

what molecule is involved in energy transfer which is then readily converted to ATP?

A

GTP

21
Q

what is the order of intermediates from CAC starting from citrate? (8)

A
  1. citrate
  2. isocitrate
  3. alpha-ketoglutarate
  4. succinyl-CoA
  5. Succinate
  6. fumarate
  7. malate
  8. oxaloacetate
22
Q

what 2 molecules are released between isocitrate and alpha-ketoglutarate?

A
  • NADH

- CO2

23
Q

what 2 molecules are released between alpha-ketoglutarate and succinyl-CoA?

A
  • NADH

- CO2

24
Q

what is released at succinate intermediate

A

GTP

25
Q

what is released between succinate and fumarate intermediates?

A

FADH2

26
Q

what is release at oxaloacetate intermediate?

A

NADH

27
Q

between which two steps in the CAC is CoA group removed completely?

A

between succinyl CoA and succinate steps

28
Q

If the cell has enough energy, what will happen to the production of pyruvate dehydrogenase?

A

it will be stopped/ inhibited

29
Q

what 3 things can inhibit pyruvate dehydrogenease that makes acetyl CoA

A
  • ATP
  • NADH
  • acetyl CoA
30
Q

what 2 things can stimulate production of pyruvate dehydrogenase to make acetyl CoA?

A
  • ADP

- pyruvate

31
Q

at what 2 intermediates in CAC, are the other control points?

A
  1. isocitrate

2. alpha-ketoglutarate

32
Q

What sort of reactions are the control points in CAC?

A

non-reversible reactions (exergonic steps, deltaG -ve)

33
Q

what 2 things inhibit isocitrate dehydrogenase?

A
  1. ATP

2. NADH

34
Q

what stimulates isocitrate dehydrogenase?

A

ADP

35
Q

what 3 things inhibit alpa-ketoglutarate dehydrogenase?

A
  • ATP
  • NADH
  • succinyl CoA
36
Q

are isocitrate and citrate interconvertible?

A

yes

37
Q

if there is citrate build up when isocitrate dehydrogenase stops working, what happens?

A

citrate is shuttled into cytoplasm causing phosphofructokinase to stop glycolysis

38
Q

what happens if there is a build up of alpha-ketoglutarate if alpha-ketoglutarate dehydrogenase is inactive?

A

alpha-ketoglutarate switches its use to production of amino acids

39
Q

what sort of pathway is CAC?

A

amphibolic pathway (both catabolic and anabolic processes occur)

40
Q

what does build up of citrate produce? (2)

A

fatty acids, sterols

41
Q

what does build up of alpha-ketoglutarate produce?

A
  • glutamate (leading to AAs like glutamine, proline, arginine etc) and purines
42
Q

what does build up of succinyl CoA produce?

A

porphyrins, heme

43
Q

what enzyme is used to convert pyruvate to oxaloacetate?

A

pyruvate carboxylase

44
Q

what sort of a reaction is conversion of pyruvate to oxaloacetate?

A

anabolic process (formation)

45
Q

what are the 3 main products produced as a result of intermediates from CAC building up?

A
  1. nucleotide bases
  2. heme groups
  3. proteins
46
Q

if there is a build up of Acetyl CoA (excessive production) during exercise, what needs to be produced more of to keep CAC going?

A

oxaloacetate

47
Q

what pathway can produce oxaloacetate directly?

A

Pyruvate can be converted to oxaloacetate through pyruvate carboxylase

48
Q

what is the term given to conversion of pyruvate to oxaloacetate by pyruvate carboxylase?

A

anaplerotic

SfM topics (21 decks)

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