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Biochemistry > 11.2 Electron Transport Chain > Flashcards

11.2 Electron Transport Chain Flashcards

1
Q

where do glycolysis, citrate cycle, and electron transport chain take place?

A

glycolysis: cytosol
citrate cycle: mitochondrial matrix
electron transport chain: inner mitochondrial membrane

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2
Q

what 2 compounds feed the electron transport chain?

A

NADH and FADH2

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3
Q

what are the 2 main routes of electron transport through the ETC?

A
  1. oxidation of NADH on matrix of IMM
  2. oxidation of FADH2 from either the cytosolic side or the matrix side of IMM
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4
Q

how many protons are pumped by the oxidation of NADH on the matrix side of the IMM?

A

10!!!

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5
Q

what is the electron flow of oxidation of NADH on the matrix side of the IMM? (7)

A
  1. NADH
  2. complex I/NADH-ubiquinone oxidoreductase
  3. Q
  4. complex III/ ubiquinone-cytochrome c oxidoreductase
  5. cytochrome c
  6. complex IV/cytochrome c oxidase
  7. O2
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6
Q

how many H+ are pumped from the oxidation of FADH2 of the cytosolic side or matrix side of IMM?

A

6!

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7
Q

what is the electron flow of the oxidation of FADH2 on the cytosolic or matrix side of the IMM? (7)

A
  1. FADH2
  2. complex II/succinate dehydrogenase
  3. Q
  4. complex III/ubiquinone-cytochrome c oxidoreductase
  5. cytochrome c
  6. complex IV/cytochrome c oxidase
  7. O2
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8
Q

why does oxidation of FADH2 pump less protons than oxidation of NADH?

A

complex II (succinate dehydrogenase) does not pump electrons!

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9
Q

what is an alternate path for the oxidation of FADH2? what does this path also produce?

A

oxidizing fatty acids bt ETF-Q oxidoreductase; also produces acetyl CoA

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10
Q

what are the 4 components of the electron transport chain?

A
  1. complexes I, II, IV
  2. 3 membrane associated FAD/FADH2 containing enzymes
  3. coenzyme Q (ubiquinone)
  4. cytochrome c
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11
Q

describe complexes I, III, IV of the ETC

A

large, multi-subunit complexes that translocate proteins across IMM

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12
Q

what do the 3 membrane associated FAD/FADH2-containing enzymes do?

A

provide 3 routes for FADH2 entry into the ETC

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13
Q

what are the 3 membrane-associated FAD/FADH2 containing enzymes? describe

A
  1. complex II (succinate dehydrogenase): from glycolysis
  2. ETF-Q oxidoreductase: for lipid metabolism
  3. glycerol-3-phosphate dehyrogenase: cytosolic NADH
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14
Q

describe coenzyme Q (ubiquinone) (2)

A
  1. small, hydrophobic electron carrier that diffuses through the membrane
  2. can transfer 2 electrons from complex I or II to complex III
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15
Q

describe cytochrome c (2)

A
  1. small, water soluble protein in intermembrane space
  2. transfers 1 electron from complex III to complex IV
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16
Q

which components of the ETC are immobile?

A
  1. complexes I, III, IV
  2. the 3 membrane associated FAD/FADH2-containing enzymes
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17
Q

what does complex I NADH-ubiquinone oxidoreductase do?

A

oxidized NADH, reduces ubiquinone

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18
Q

what does complex III ubiquinone-cytochrome c oxidoreductase do?

A

oxidizes ubiquinone, reduces cytochrome c

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19
Q

what does complex IV, cytochrome oxidase do?

A

oxidizes cytochrome c so electrons can end up on O2 to make H20

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20
Q

where are protein bound redox centers found?

A

bound to proteins in the ETC

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21
Q

list and describe 3 protein-bound redox centers in the ETC

A
  1. iron-sulfur or copper centers: can carry one electron only
  2. hemes: can carry only one electron
  3. coenzymes FADH2 or FMN: can carry 1 or 2 electrons
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22
Q

what are the 2 mobile electron carriers in the ETC? describe

A
  1. coenzyme Q (ubiquinone): a small molecule that can carry 1 or 2 electrons
  2. cytochrome c: a small protein that can only carry one electron
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23
Q

what can coenzyme Q (ubiquinone) do?

A

can form a semiquinone intermediate to hold 1 electron at a time

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24
Q

what is the largest of the 4 complexes in the ETC?

A

complex I; NADH-ubiquinone oxidoreductase

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25
Q

how many protons does complex I; NADH-ubiquinone oxidoreductase, pump into the intermembrane space?

A

4

26
Q

what does complex I, NADH-ubiquinone oxidoreductase do? (3)

A
  1. pumps 4 protons into intermembrane space
  2. oxidizes NADH
  3. reduces Q
27
Q

what does complex I; NADH-ubiquinone oxidoreductase, contain? (2) describe each

A
  1. flavin mononucleotide: transports 1 or 2 electrons
  2. contains over 7 Fe-S centers that carry 1 electron at a time
28
Q

describe electron flow through complex I; NADH-ubiquinone oxidoreductase

A
  1. NADH transfers 2 electrons to FMN
  2. 2 electrons are transferred from carrier to carrier until
  3. 2 electrons and 2 protons bind Q, forming QH2, which leaves to go to complex III (ubiquinone cytochrome c oxidoreductase)
29
Q

what is the overall result of the net reaction of complex I; NADH-ubiquinone oxidoreductase? (2)

A
  1. transfers 2 electrons from NADH to coenzyme Q
  2. 4 H+ are translocated from matrix to the intermembrane space (N side to P side)
30
Q

what is the net reaction of complex I; NADH-ubiquinone oxidoreductase?

A

NADH + Q + 5H+(from N side) –> NAD+ + QH2 + 4 H+ (to p side)

31
Q

as a mobile electron carrier, what does coenzyme Q do?

A

carries electrons from complex I or II to complex III

32
Q

what does coenzyme Q serve as?

A

the entry point for electron pairs into the electron transport chain from citate cyle, fatty acid oxidation, or G3P dehydrogenase

33
Q

why is coenzyme Q known as an adapter?

A

it can adapt between carrying 1 or 2 electrons by forming a semiquinone intermediate

34
Q

what does complex II (succinate dehydrogenase) NOT do?

A

does NOT pump protons

35
Q

what does complex II (succinate dehydrogenase) do? (3)

A
  1. catalyzes step 6 in citrate cycle
  2. reduces FAD to FADH2
  3. reduces Q to QH2
36
Q

what does complex II (succinate dehydrogenase) contain? describe

A

three Fe-S centers and a b-type heme; both of which can only carry one electron at a time

37
Q

describe the flow of electrons through complex II (succinate dehydrogenase)

A
  1. electrons enter complex II and FADH2 is oxidized to FAD (which carries 2 electrons)
  2. 2 electrons are passed to the Fe-S centers, and then through the b-type heme
  3. the 2 electrons are then used to reduce Q to QH2, which leaves and goes to complex III
38
Q

what are the 3 main takeaways from complex II (succinate dehydrogenase)?

A
  1. oxidizes FADH2 to FAD
  2. reduced Q to QH2
  3. NO translocation of H+
39
Q

what is the net reaction of complex II (succinate dehydrogenase)?

A

FADH2 + Q –> FAD + QH2

40
Q

what is complex III (ubiquinone cytochrome c oxidoreductase)? how many protons does it pump into the intermembrane space?

A

a dimeric comples that pumps 4 protons into the intermembrane space

41
Q

what does complex III (ubiquinone-cytochrome c oxidoreductase) contain? how many electrons can they hold? (3)

A
  1. 2 Fe-S centers
  2. 2 b-type hemes
  3. 1 c-type heme
    all can only transport 1 electron at a time
42
Q

what does complex III (ubiquinone-cytochrome c oxidoreductase) do? (2)

A
  1. oxidizes QH2; 1 or 2 electrons at a time
  2. reduces cytochrome C, 1 electron at a time
43
Q

what are the 2 main takeaways of the complex III (ubiquinone-cytochrome c oxidoreductase) net reaction?

A
  1. transfers 2 electrons from QH2 to 2 cytochrome c’s
  2. translocation of 4 H+ to intermembrane space
44
Q

what is the net reaction of complex III (ubiquinone-cytochrome c oxidoreductase)?

A

QH2 + 2 H+ (from N side) +2 cytochrome c (oxidized)–> Q + 4 H+ (to positive side) + 2 cytochrome c (reduced)

45
Q

why is there only 1 QH2 and 1 Q in the net reaction for complex III?

A

because 1 QH2 leaves

46
Q

when does the Q cycle take place?

A

in complex III

47
Q

what is the end result of the Q cycle?

A

converts 2 electron transfers to 1 electron transfer

48
Q

what are the 2 binding sites for QH2 called in complex III in the Q cycle?

A

Qp on positive intermembrane side and Qn on negative, matrix side

49
Q

why does the Q cycle exist?

A

QH2 carries 2 electrons at a time to complex III but cytochrome c can only carry one electron at a time to complex IV

50
Q

describe the Q cycle (4)

A
  1. QH2 binds at Qp site and 1 electron is removed and passed to cytochrome c as QH2 is oxidized and the other electron passes through 2 b type hemes as 2 H+ are pumped to the p side
  2. the oxidized Q moves to the Qn binding site, and a second QH2 binds to the Qp binding site
  3. the Q in the Qn site receives the electron from the 1st QH2 and is reduced to a semiquinone and 2nd QH2 in the Qp binding site releases one of its electrons to a second cytochrome c and 2 more H+ are pumped to p side
  4. the second electron from the 2nd QH2 in the Qp binsing site makes its way to the semiquinone in the Qn site and the smeiquinone is reduced to QH2 and leaves
51
Q

what is cytochrome c?

A

a small protein associated with the cytosolic side of the intermembrane space

52
Q

what does cytochrome c do? how?

A

carries one electron at a time from complex III to complex IV via a c-type heme group attached to its cysteine

53
Q

what is complex IV also called?

A

cytochrome c oxidase

54
Q

what does complex IV, cytochrome c oxidase, do? (3)

A
  1. pumps 2H+ into intermembrane space
  2. oxidizes cytochrome c
  3. reduces O2
55
Q

what does cytochrome c oxidase, complex IV, contain that allows it to reduce O2? (2)

A
  1. 2 Cu centers
  2. 2 hemes
56
Q

what is the net reaction for complex IV of the ETC?

A

2 cytochrome c (reduced) + 4H+(n side) + 1/2O2 –> 2 cytochrome c (oxidized) + 2H+ (p side) + H2O

57
Q

what is the result of complex IV reaction? (2)

A
  1. transfer 2 electrons from cytochrome c to O2
  2. translocation of 2H+ into intermembrane space
58
Q

what can be produced during the reduction of O2 to H2O that can harm the body how?

A

reactive oxygen species; can be carcinogens

59
Q

give 4 main points to remember about the ETC

A
  1. complexes 1,3, and 4 pump protons into the intermembrane space
  2. 10 protons are pumped per NADH
  3. 6 protons are pumped per FADH2
  4. O2 is reduced to H2O
60
Q

an you make it all the way through the electron transport chain with just 1 NADH or 1 FADH2? why or why not?

A

no! need 2 NADH or 2 FADH2 because it takes 4H+ and 4 electrons to reduce so that you don;’t actually have 1/2 O2 (because that doesn’t exist)

Biochemistry (20 decks)

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