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Biochemistry > Chapter 14: ETC and ATP Synthesis > Flashcards

Chapter 14: ETC and ATP Synthesis Flashcards

1
Q

what is the purpose of the ETC?

A

transfer of electrons to establish a proton gradient

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2
Q

what are the starting molecules of the ETC?

A

NADH and FADH2

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3
Q

what is the final product of the ETC?

A

H2O

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4
Q

what is the purpose of the ETC establishing a proton gradient?

A

the free energy stored in the proton concentration gradient is used by ATP synthase to convert ADP to ATP

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5
Q

how many membranes does the mitochondria have?

A
  • TWO
  • outer membrane- freely permeable to small molecules
  • inner membrane- impermeable to polar and ionic substances
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6
Q

where are the enzyme complexes located that catalyze the reactions of the ETC and ATP synthesis?

A

inner membrane

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7
Q

What is the chemiosmotic theory?

A

states that the energy from the oxidation-reduction reactions of electron transport is used to create a proton gradient across the membrane and that gradient is then used for the synthesis of ATP

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8
Q

what is the protonmotive force?

A
  • refers to the potential energy associated with a proton gradient
  • due to the combined effect of a charge difference and a proton concentration difference across the membrane
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9
Q

how was the chemiosmotic theory and proton motive force proved?

A
  • *by a synthetic vesicle containing a light-powered proton pump (bacteriorhodopsin) and ATP synthase
    • when the vesicle was exposed to light, ATP was formed
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10
Q

what are the complexes located in the electron transport chain?

A
  • Complex 1: NADH-Q oxidoreductase
  • Complex 2: Succinate-Q oxidoreductase - same as succinate dehydrogenase complex in krebs cycle
  • Complex 3: Q-cytochrome c oxidoreductase
  • Complex 4: Cytochrome c oxidase
  • Complex 5: ATP Synthase
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11
Q

what are the mobile coenzymes that serve as links between the different complexes of the ETC?

A

Coenzymes Q and cytochrome c

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12
Q

what direction do electrons flow in the ETC?

A

in the direction of increasing reduction potential

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13
Q

what are the prosthetic groups of complex 1?

A
  • FMN

- Fe-S

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14
Q

what are the prosthetic groups of complex 2?

A
  • FAD

- Fe-S

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15
Q

what are the prosthetic groups of complex 3?

A
  • heme b(H)
  • heme b(L)
  • heme c1
  • Fe-S
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16
Q

what are the prosthetic groups of complex 4?

A
  • heme a
  • heme a3
  • Cu A
  • Cu B
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17
Q

what is the role of complex 1 (NADH-Q oxidoreductase)?

A
  • catalyzes the transfer of two electrons from NADH to Q, forming QH2
  • 4 protons are transferred across the membrane for every pair of electrons that pass from NADH to Q
  • contributes to proton gradient
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18
Q

how do the electrons pass through the prosthetic groups of complex 1?

A
  • two electrons pass from NADH to FMN –> FMNH2
  • FMNH2 pass the electrons one at a time to Fe-S
  • Fe-S transfers electrons one at a time to Q –> QH2
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19
Q

what is the role of complex 2 (succinate-Q oxidoreductase)?

A
  • accepts the electrons from succinate and ultimately transfers them to Q –> QH2
  • does not contribute to proton gradient
  • very little free energy is released
  • supplies electrons from the oxidation of succinate
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20
Q

how do the electrons pass through the prosthetic groups of complex 2?

A
  • two electrons are transferred from succinate to FAD, forming FADH2
  • FADH2 then passes single electrons to Fe-S
  • Fe-S transfers electrons one at a time to Q to form QH2
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21
Q

what is the role of complex 3 (Q cytochrome c oxidoreductase)?

A
  • catalyzes the oxidation of QH2 in the membrane and the reduction of cytochrome c in the intermembrane space
  • contributes to the proton gradient
22
Q

how do the electrons flow through the prosthetic groups of complex 3?

A
  • two pairs of electrons are passed separately from two molecules of QH2
  • each pair is split so electrons follow separate pathways
  • one electron is transferred to an Fe-S cluster, then to cytochrome c1, and finally to cytochrome c
  • one electron is transferred to heme bH and then to Q (part of Q cycle)
23
Q

why is the flow of electrons through complex 3 different than the others?

A

-electron transport through complex 3 is coupled to the transport of protons across the membrane in a process called the Q cycle

24
Q

what is the net effect of the Q cycle?

A
  • the transfer of 4 protons to the intermembrane space for every two electrons transferred from QH2 to cytochrome c
  • two protons come from QH2 and two come from the mitochrondrial matrix
25
Q

what is the Q cycle?

A
  • describes a pair of reactions within complex 3 (at Q0 and Q1) in which the sequential oxidation and reduction Q between its ubiquinol and ubiquinone forms, results in the net movement of protons across the inner mitochondrial membrane
  • net result is that cytochrome c is reduced and protons are pumped into the intermembrane space
26
Q

what is the role of complex 4 (cytochrome c oxidase)?

A
  • catalyzes the oxidation of reduced cytochrome c molecules produced in complex 3
  • contributes to proton gradient
  • electrons transferred from cytochrome c to O2 –> H2O
27
Q

how do the electrons flow through the prosthetic groups of complex 4?

A
  • cytochrome c binds to the enzyme and transfers an electron to the CuA site in the enzyme
  • the complete oxidation of O2 required 4 electrons, so 4 molecules of cytochrome c have to bind and sequentially transfer a single electron each to the CuA redox center
  • electrons are transferred one at a time from the CuA site to the heme a prosthetic group
  • electrons are then transferred one at a time from the heme a prosthetic group to the heme a3 - CuB binuclear center
28
Q

how is oxygen reduced in complex 4?

A

-the site where oxygen is reduced is buried within the protein in the middle of the lipid bilayer, so charged protons cannot enter the site by passive diffusion - the enzyme has a channel through which protons can pass

29
Q

which complexes of the ETC can transfer protons from the mitochondrial matrix into the intermembrane space?

A

complexes I, III, and IV

30
Q

for every pair of electrons that go through the ETC, how many protons translocate?

A

10 protons

31
Q

what is the role of complex 5 (ATP synthase)?

A

-catalyzes the synthesis of ATP from ADP and Pi in a reaction that is driven by the proton gradient generated during the ETC

32
Q

what is the role of the F0 subunit of ATP synthase?

A
  • embedded in the inner membrane

- contains the proton channel of the subunit

33
Q

what is the role of the F1 subunit of ATP synthase?

A
  • located in the mitochondrial matrix
  • contains central gamma subunit that serves as a shaft around which the alpha and beta subunits (3 of each, alternating) rotate
34
Q

how do the alpha and beta subunits of F1 work?

A
  • each alpha subunit binds ATP but these nucleotides do not participate in any reactions
  • beta subunits undergo conformational changes
35
Q

what are the steps of the beta subunit conformational changes?

A
  • **rotation of the gamma subunit interconverts the 3 beta subunits
    1. ADP and Pi bind to an open site
    2. rotation of the gamma shaft causes each of the catalytic sites to change conformation; the open conformation (ADP and Pi) becomes loose; the loose site, already ADP and Pi, becomes tight; the site containing ATP becomes open
    3. ATP is released from the open site and ADP and Pi condense to form ATP in the tight site
36
Q

describe the flow of the beta subunits of ATP synthase

A

Open (release ATP, recruit ADP + Pi) –> loose (bind ADP + Pi) –> tight (catalyze formation of ATP) –> open

37
Q

when does the interconversion of beta subunits occur?

A

the interconversion occurs when the gamma subunit use the energy associated with the proton gradient to turn, causing conformational changes in the beta subunits

38
Q

how is ATP in the mitochondria transported to the cytoplasm?

A
  • adenine nucleotide translocase
  • carries out unidirectional exchange of ATP for ADP (antiport)
  • symport of Pi and H+ draws on the concentration gradient of H+
  • *ATP goes to intermembrane space
  • *ADP, Pi, and H+ go to matrix
39
Q

which NADH molecules in eukaryotes have access to complex 1 of the ETC?

A

NADH in the mitochondrial matrix

40
Q

what is the purpose of the glycerate phosphate shuttle?

A

allows electrons from NADH outside the matrix to enter the ETC through reduction of dihydroxyacetone

41
Q

what is the purpose of the malate aspartate shuttle?

A
  • uses NADH in the cytosol to reduce oxaloacetate to malate
  • malate can be transported to the mitochondrial matrix and reoxidized to generate NADH, which can pass electrons into the ETC
42
Q

what is an unfortunate consequence of oxidative phosphorylation?

A
  • the release of reactive oxygen species (toxic)
  • superoxide radical
  • hydroxyl radical
  • hydrogen peroxide
43
Q

what is the role of superoxide dismutase?

A
  • converts superoxide to hydrogen peroxide

- hydrogen peroxide can then be converted to water and oxygen by catalase

44
Q

what are some compounds that target any of the complexes I-IV in the ETC?

A
  • carbon monoxide
  • cyanide
  • sodium azide
  • rotenone
  • antimycin A
  • amytal
45
Q

what is the result of inhibitors of the complexes of the ETC?

A

any compound that stops electron transport will stop respiration - you will stop breathing

46
Q

what is a compound that targets the F0 subunit of ATP synthase?

A

oligomygin

47
Q

what is the result of inhibitors of the F0 subunit of ATP synthase?

A

electron transport can be stopped by stopping ATP synthesis

48
Q

what are some uncouplers that target the proton gradient?

A
  • 2,4-dinitrophenol

- trifluoricarbonylcyanide phenylhydrazone

49
Q

what is the result of the uncouplers of the proton gradient?

A

an uncoupler breaks the connection between the ETC and ATP synthesis - ETC happens without making any ATP

50
Q

what is the mechanism of uncouplers?

A
  • *uncouplers stimulate the oxidation of substrates in th absence of ADP
  • electron transport is happening, but ATP synthesis is not
  • heat is generated instead
  • uncoupling protein-1 does this in brown adipose tissue
  • common in hibernating animals

Biochemistry (9 decks)

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