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MCB 3010 > EXAM 3: CAC > Flashcards

EXAM 3: CAC Flashcards

1
Q

cellular respiration

A

complete oxidation

cells consume O2 and produce CO2

captures energy stored in lipids and amino acids

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2
Q

3 stages of cellular respiration

A

acetyl-coa production

acetyl-coa oxidation

electron transfer and oxidative phosphorylation

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3
Q

glycolysis location

A

cytosol

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4
Q

citric acid cycle location

A

mitochondrial matrix (except succinate dehydrogenase on inner membrane)

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5
Q

oxidative phosphorylation location

A

inner membrane

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6
Q

pyruvate to acetyl-CoA

A

required for pyruvate from glycolysis to enter CAC

not required for fatty acid catabolism

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7
Q

result of reaction

pyruvate —> acetyl-Coa

A

oxidative decarboxylation of pyruvate

first carbons of glucose to be fully oxidized

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8
Q

what catalyzes pyruvate to acetyl-coa

A

pyruvate dehydrogenase complex

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9
Q

pyruvate dehydrogenase complex

A

5 cofactors

prosthetic groups: TPP, lipoyllysine, FAD

coenzymes: NAD+, CoA-SH

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10
Q

coenzyme A

A

not a permanent part of enzymes structure

associate, fulfill reaction, dissociate

in this rxn, carries and accepts acetyl groups

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11
Q

pyruvate dehydrogenase complex (PDC)

A

multiple copies of 3 enzymes

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12
Q

advantages of multienzyme complex in PDC

A

short distance between catalytic sites, allows channeling of substrates from one catalytic site to another

channeling minimizes side reactions

regulation of activity of one subunit affects entire complex

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13
Q

sequence of events in oxidative decarboxylation of pyruvate

A

step 1: pyruvate is decarboxylated to an aldehyde; prosthetic group TPP attaches
=hydorxyethyl TPP

step 2: lipoyl cofactor is reduced (disulfide bonds break) and binds the aldehyde to form thioester
oxidizes aldehyde

step 3: first main product of acetyl-CoA

step 4: reduced lipoyllysine is reoxidized (recycled) with reduction of FAD to FADH2

step 5: regeneration of oxidized FAD cofactor forms reduced NADH (product 2)

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14
Q

net result of citric acid cycle

A

acetyl-CoA + 3NAD+ FAD + GDP + Pi + 2H2O

2 CO2 + 3NADH + FADH2+ GTP + CoA + 3H+

energy captured by electron transfer to NADH and FADH2

GTP can be converted to ATP

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15
Q

citric acid cycle name

A

citrate is made first

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16
Q

TCA cycle name

A

tricarboxylic acid cycle; first 2 molecules made have 3 carboxyl groups

citrate, isocitrate

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17
Q

krebs cycle name

A

hans krebs in 1937

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18
Q

CAC: Step 1

A

acetyl-CoA + oxaloacetate + H2O —> citrate + CoA-SH

C-C bond formation by condensation of acetyl-CoA and oxaloacetate

citrate synthase

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19
Q

CAC Step 1: citrate synthase reaction

A

condensation of acetyl-Coa and oxaloacetate

rate limiting step of CAC

activity largely depends on [oxaloacetate]

favorable, irreversible (regulated by substrate availability and product inhibition)

ordered sequential; oxaloacetate then acetyl-coa

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20
Q

CAC: Step 2

A

citrate —> cis-aconitate + H2O —> isocitrate

isomerization by dehydration / rehydration

aconitase

21
Q

CAC Step 2: aconitase reaction

A

isomerizes molecule by removing then adding h2O

  • elimination of H2O from citrate gives cis c=c bond
  • addition of H2O to cis-aconitrate is stereospecific
  • citrate = tert alc; poor substrate for oxidation
  • isocitrate = secondary alc,good substrate

unfavorable,reversible; low product

22
Q

why is isocitrate a better substrate for oxidation?

A

2 hydrogens to remove; one on the alc, and one on the alcohol the carbon is attached to

23
Q

CAC: Step 3

A

isocitrate + NAD+ —> a-ketoglutarate + NADH + CO2

oxidation decarboxylation of isocitrate

isocitrate dehydrogenase

24
Q

CAC Step 3: isocitrate dehydrogenase reaction

A

catalyzes oxidative decarboxylation

  • generates NADH
  • lose carbon as CO2 (complete oxidation)

oxidation converts alcohol to ketone; transfers hydride to NAD+

carboxyl group on C3 leaves

favorable, irreversible; product inhibition and ATP allosteric regulation

25
Q

CAC: Step 4

A

a-ketoglutarate + CoA-SH + NAD+ —> succinyl-CoA + CO2 + NADH

final oxidative decarboxylation

alpha-ketoglutarate dehydrogenase complex

26
Q

CAC Step 4: alpha-ketoglutarate dehydrogenase rxn

A

net full oxidation of all carbons of acetyl-CoA

after two turns: complete oxidation of all carbons from glucose

ketone oxidized to thioester; NAD+ reduced

succinyl-CoA has a higher energy thioester bond

favorable, irreversible; product inhibition

27
Q

a-ketoglutarate dehydrogenase

A

complex similar to pyruvate dehydrogenase

same coenzymes, identical mechanisms; active sites different for diff sized substrates

28
Q

CAC: Step 5

A

succinyl-CoA + GDP + Pi —> GTP + CoA-SH + succinate

generation of GTP through thioester bond cleavage

succinyl-CoA synthetase

29
Q

CAC Step 5: succinyl-CoA synthetase reaction

A

substrate level phosphorylation

energy of breaking thioester bond allows incorporation of Pi to make GTP

  • Pi displaces CoA to make succinyl phosphate
  • Pi transferred to make phospho-enzyme intermediate; succinate leaves
  • Pi added to GDP to produce GTP

can be converted to ATP

favorable, reversible; low product

30
Q

Step 5 isozymes in brain, muscle, heart

A

use ADP, make ATP

31
Q

Step 5 isozymes in liver, kidney

A

GTP, GDP

32
Q

CAC: Step 6

A

succinate + FAD —> FADH2 + fumarate

oxidation of alkane to alkene

succinate dehydrogenase

33
Q

CAC Step 6: succinate dehydrogenase rxn

A

in inner membrane

oxidation of alkane to alkene; reduction of FAD to FADH2

reversible; low product concentration

34
Q

why isn’t NAD+ used in step 6 in the succinate dehydrogenase reaction?

A

reduction potential is too low

35
Q

CAC: Step 7

A

fumarate + OH- —> carbanion TS + H+ —> L-malate

hydration across a double bond

fumarase

36
Q

CAC Step 7: fumarase reaction

A

stereospecific

addition of water is trans, forms L-malate

  • OH- adds fumarate first, then H+ to carbanion
  • cannot distinguish between inner carbons, so either can gain OH-

favorable, reversible; low product

37
Q

CAC: Step 8

A

L-malate + NAD+ —> NADH + H+ + oxaloacetate

oxidation of alcohol to ketone

malate dehydrogenase

38
Q

CAC Step 8: malate dehydrogenase reaction

A

final step

alcohol on malate oxidized to ketone; NAD+ reduced

regenerates oxaloacetate for citrate synthesis

unfavorable, reversible; oxaloacetate kept very low by citrate synthesis to pull reaction forward

39
Q

how many NADH are made for CAC?

A

3 per cycle; 6 per glucose

40
Q

how many FADH2 made per CAC?

A

1 per cycle; 2 per glucose

41
Q

how many GTP/ATP made per CAC***?

A

1 per cycle; 2 per glucose

42
Q

how many Co2 formed in CAC?

A

2 per cycle; 4 per glucose

43
Q

4 reactions in CAC with regulation

A

pyruvate dehydrogenase

citrate synthase

isocitrate dehydrogenase

alpha-ketoglutarate dehydrogenase

44
Q

regulatory mechanism in CAC

A

activation: substrate availability
NAD+, AMP, ADP

inhibition: product accumulation
ATP, NADH

enzymes may be associated to allow channeling

45
Q

amphibolic intermediates

A

intermediates can go into other pathways

but if they are taken out, cycle isn’t completed, and oxaloacetate will run out

46
Q

catabolic

A

further break down

47
Q

anabolic

A

makes other molecules

48
Q

anapleurotic reactions

A

intermediates in CAC can be used in biosynthetic pathways (removed from CAC)

must replenish the intermediates in order for the cycle and central metabolic pathway to continue

3 carbon intermediates (pyruvate, phosphoenolpyruvate) are carboxylated to form 4 carbon intermediates (oxaloacetate, malate)

malate is one step away from oxaloacetate

MCB 3010 (12 decks)

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