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BIOC192 > 30 > Flashcards

30 Flashcards

1
Q

Acetyl-CoA
Structure

A
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2
Q

Other names of cytric acid cycle (CAC)

A

Also called the Tricarboxylic acid (TCA) Cycle or the Krebs Cycle

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3
Q

Where does the cytric acid occur

A

Occurs in the mitochondria

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4
Q

Where are the enzymes that carry out the CAC located

A

All but one enzymes is in the mitochondrial matrix

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5
Q
A
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6
Q

CoA is already in the

A

Mitochondral matrix

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7
Q

Cytric acid starts and finishes with

A

The same molecule - CoA

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8
Q

Carbon ____ and ____ the cytric acid cycle… what do the two C enter as?

A

Carbon enters and leaves the cytric acid as acetyl-CoA

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9
Q

Where does acetyl-CoA come from?

A

Both glycolysis (aerobic, PDH reaction) and β-oxidation produce acetyl-CoA in the mitochondria

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10
Q

Carbons in the citric acid cycle

A

Carbon enters and leaves
- 2 C in as acetyl-CoA
- 2 C out as 2 X CO2
(oxidation complete)

Captures energy: - 1 ATP - 3 NADH and 1 FADH2

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11
Q

Citric acid cycle - first part involves …

A
  1. Release of C
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12
Q

Citric acid cycle - second part involves …

A

Regeneration of the starting molecule

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13
Q

Energy is captured in ______ parts of the cytric acid cycle

A

Both

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14
Q

Condensation of acetyl- CoA with oxaloacetate

A

2 C entering the CAC as acetyl-CoA is attached to 4 C oxaloacetate to produce 6 C citrate

Energy for the reaction comes from the hydrolysis of CoA from acetyl-CoA - energetically favourable - ΔG0´= -32.8 kJ/mol

Because the CAC is a “cycle” these two carbons need to be removed

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15
Q

Isomerisation of citrate

A

Rearrangement of citrate to isocitrate makes the molecule susceptible to decarboxylation

Both steps catalyzed by aconitase

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16
Q

Isomerisation of citrate - both reactions are catalyzed by

A

aconitase

17
Q

Targeting the CAC to kill …
What happens when we consume fluoroacetate ?

A
  • Fluoroacetate is metabolised to fluorocitrate
  • reaction that adds acetyl-CoA
  • instead of an H there is an F
  • citrate snythase can tell the difference so it gets added to oxaloacetate
18
Q

Isomerisation of citrate - FLUOROACETATE

A

Rearrangement of citrate to isocitrate makes the molecule susceptible to decarboxylation

Both steps catalysed by aconitase

Fluorocitrate is converted into a substrate that binds tightly to aconitase and inactivates the enzyme

19
Q

Consequences of inhibiting the CAC

A
  • increased acetyl-CoA (build up of acetyl CoA, increase dalta G values till it reaches unfavourable kenetically and then other processes such as B oxidation also wont be happening - YAP)
  • decreased reduced coenzymes
  • less ATP
20
Q

Removal of the 1st carbon

A
  • An oxidative decarboxylation
  • Reaction occurs in two steps: oxidation then
    decarboxylation
  • Energy captured in NADH

Isocitrate dehydrogenase used

21
Q

Enzyme involved in the Removal of the 1st carbon

A

Isocitrate dehydrogenase

22
Q

Removal of the 2nd carbon

A
  • A second oxidative decarboxylation
  • Very similar to the pyruvate dehydrogenase reaction - complex
  • Energy captured in NADH

Adding on a

Enzyme = α −ketoglutarate dehydrogenase

ΔG0 ´= -33.4 kJ/mol

23
Q

Citric Acid Cycle: Summary one part

A
  • two carbons removed
  • energy conserved as NADH
  • a 4C molecule has been regenerated (succinyl-CoA)

The rest of the cycle is concerned with regenerating oxaloacetate and capturing more energy

24
Q

Succinyl-CoA to succinate

A

The removal of the CoA releases enough energy to drive the synthesis of GTP

GTP is the energy equivalent of ATP:
- GTP + ADP <===> GDP + ATP

The 3rd substrate level phosphorylation (in pathways)

25
Q

Substrate-level phosphorylation
- where does the phosphate come from

A
  • doesnt matter - can come from the substrate like in glycolysis or come from solution in Succinyl-CoA to succinate
26
Q

Succinate to oxaloacetate

A
27
Q

Succinate to oxaloacetate - what is it simlat to?

A

The reactions used to convert succinate to oxaloacetate are very similar to β-oxidation

28
Q

A shared reaction
- succinate —-> fumarate

A

SDH is located in the inner mitochondrial membrane

SDH uses FAD as a coenzyme: flavin (FAD) coenzymes are tightly bound to the proteins with which they interact (flavoproteins)

SDH is part of CAC where FAD is reduced, so needs to also be in the electron transport chain (ETC) to oxidize FADH2 back to FAD (- electron transport chain is in the inner mitochondrial membrane Hanse why SDH is located there)

29
Q

succinate + E-FAD ➞ fumarate + E-FADH2

A
30
Q

Overall reaction for the CAC

A
31
Q

Overall reaction for the CAC

A

BIOC192 (38 decks)

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