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Biochem 2 > TCA cycle > Flashcards

TCA cycle Flashcards

1
Q

What are the three main things to follow when going through the TCA cycle rxns?

A

-# of carbons and where they are
-movement of electrons
-follow the energy (delta G)

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2
Q

How many reactions are there in TCA cycle?

A

8 reactions

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3
Q

What is the output from 1 acetyl-CoA?

A

-2 CO2
-1 ATP
-3NADH/H+
-1 FADH2

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4
Q

Roughly how much ATP is 1 NADH equivalent to?

A

~2.5 ATP = 1 NADH

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5
Q

roughly how much ATP is 1 FADH equivalent to?

A

~1.5 ATP = 1 FADH

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6
Q

What is a metabolon?

A

-group of enzymes performing reactions with a common function
-these enzymes can be localized in organelle or part of organelle
-seen in glycolysis, gluconeogen, FA synth, and ETC

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7
Q

What is substrate channeling?

A

-when the product of one rxn directly becomes the substrate for the next rxn
-used for small molecules (1-2C)
-uses biological tethers
-ex. Co-A in acetyl-CoA

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8
Q

What is important about Acetyl-CoA?

A

-important intermediate
-product of pyruvate oxidation
-product of fatty acid metabolism
-chemical bonds are energetically rich
-carries 2C acetyl group

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9
Q

Step 1: citrate synthase

A

-condensation synthesis
-acetyl-coA (2C) + oxaloacetate (4C) -> citrate (6C)
-irreversible
-favourable rxn

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10
Q

Step 2: Aconitase

A

-isomerization (sort of) = two steps of dehydration then hydration
-citrate (6C) -> isocitrate (6C)
-reversible
-near 0 G

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11
Q

What is the intermediate for the two step reaction of aconitase enzyme?

A

cis-Aconitate

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12
Q

Step 3: Isocitrate Dehydrogenase

A

-oxidation decarboxylation
-isocitrate (6C)-> a-ketoglutarate (5C) + CO2
-produces NADH/H+
-irreversible
-favourable rxn

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13
Q

Step 4: a-ketoglutarate dehydrogenase

A

-oxidation decarboxylation
-a-ketoglutarate (5) -> succinyl-CoA (4) + CO2
-NADH/H+ produced
-irreversible -> Rate Limiting
-very favourable reaction

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14
Q

What are the parts of the a-ketoglutarate dehydrogenase complex?

A

-multienzyme
-E1 = TPP decarboxylase
-E2 = dihydrolipoyl transferase
-E3 = dihidyrolipoyl dehydrogenase

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15
Q

Of the carbons lost in the first 4 steps of TCA, are they from the acetyl CoA or the oxaloacetate?

A

-they are from the oxaloacetate
-still have both C from the acetyl CoA

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16
Q

Step 5: Succinyl CoA Synthase

A

-substrate-level phosphorylation
-succinyl-CoA (4C) -> succinate (4)
-1 ATP produced via water
-reversible rxn
-near 0 G

17
Q

Step 6: Succinate Dehydrogenase

A

-oxidation
-succinate -> fumarate
-produces an FADH2
-reversible
-near 0 G

18
Q

What is fumarate?

A

a trans-dioic acid

19
Q

What is important about succinate dehydrogenase enzyme?

A

-bound to mito inner membrane
-part of Complex 2 in ETC
-near equilibrium = reversible
-FAD covalently bound
-uses FADH2 to reduce alkane to alkene because potential too low for NAD+

20
Q

Step 7: Fumarase

A

-hydration
-fumarate (4C) + water -> malate (4C)
- reversible
-energy not used or produced
-near 0 G

21
Q

Step 8: Malate Dehydrogenase

A

-oxidation
-Malate (4C) -> oxaloacetate (4C)
-reversible
-makes NADH/H+
-near 0 G = driven forward by product removal

22
Q

Which steps of TCA are irreversible?

A

step 1, 3, 4

23
Q

Which steps of TCA are reversible?

A

steps 2, 5, 6, 7, 8

24
Q

Which steps produce NADH?

A

steps 3, 4, 8

25
Q

Which step produces ATP?

A

step 5

26
Q

What step produces FADH2?

A

step 6

27
Q

What is an anaplerotic rxn?

A

rxns that replenish levels of TCA intermediates

28
Q

What does NADH inhibit?

A

all three dehydrogenases

29
Q

name 3 allosteric regulators in TCA regulation

A

-ATP
-Ca2+
-Succinyl CoA

30
Q

What is regulation based on in TCA?

A

-substrate availability

31
Q

What are the fates of the carbon atoms removed from TCA?

A

CO2

32
Q

What are the fate of the electrons removed from TCA?

A

mostly NADH (some ATP and FADH2)

33
Q

What are reducing equivalents?

A

-chemical species which transfer the equivalent of one electron in redox reactions
-NADH is a key carrier

34
Q
A

Biochem 2 (7 decks)

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