Chapter 14: ETC and ATP Synthesis Flashcards
what is the purpose of the ETC?
transfer of electrons to establish a proton gradient
what are the starting molecules of the ETC?
NADH and FADH2
what is the final product of the ETC?
H2O
what is the purpose of the ETC establishing a proton gradient?
the free energy stored in the proton concentration gradient is used by ATP synthase to convert ADP to ATP
how many membranes does the mitochondria have?
- TWO
- outer membrane- freely permeable to small molecules
- inner membrane- impermeable to polar and ionic substances
where are the enzyme complexes located that catalyze the reactions of the ETC and ATP synthesis?
inner membrane
What is the chemiosmotic theory?
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
what is the protonmotive force?
- 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
how was the chemiosmotic theory and proton motive force proved?
- *by a synthetic vesicle containing a light-powered proton pump (bacteriorhodopsin) and ATP synthase
- when the vesicle was exposed to light, ATP was formed
what are the complexes located in the electron transport chain?
- 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
what are the mobile coenzymes that serve as links between the different complexes of the ETC?
Coenzymes Q and cytochrome c
what direction do electrons flow in the ETC?
in the direction of increasing reduction potential
what are the prosthetic groups of complex 1?
- FMN
- Fe-S
what are the prosthetic groups of complex 2?
- FAD
- Fe-S
what are the prosthetic groups of complex 3?
- heme b(H)
- heme b(L)
- heme c1
- Fe-S
what are the prosthetic groups of complex 4?
- heme a
- heme a3
- Cu A
- Cu B
what is the role of complex 1 (NADH-Q oxidoreductase)?
- 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
how do the electrons pass through the prosthetic groups of complex 1?
- 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
what is the role of complex 2 (succinate-Q oxidoreductase)?
- 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
how do the electrons pass through the prosthetic groups of complex 2?
- 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
what is the role of complex 3 (Q cytochrome c oxidoreductase)?
- catalyzes the oxidation of QH2 in the membrane and the reduction of cytochrome c in the intermembrane space
- contributes to the proton gradient
how do the electrons flow through the prosthetic groups of complex 3?
- 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)
why is the flow of electrons through complex 3 different than the others?
-electron transport through complex 3 is coupled to the transport of protons across the membrane in a process called the Q cycle
what is the net effect of the Q cycle?
- 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
what is the Q cycle?
- 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
what is the role of complex 4 (cytochrome c oxidase)?
- catalyzes the oxidation of reduced cytochrome c molecules produced in complex 3
- contributes to proton gradient
- electrons transferred from cytochrome c to O2 –> H2O
how do the electrons flow through the prosthetic groups of complex 4?
- 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
how is oxygen reduced in complex 4?
-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
which complexes of the ETC can transfer protons from the mitochondrial matrix into the intermembrane space?
complexes I, III, and IV
for every pair of electrons that go through the ETC, how many protons translocate?
10 protons
what is the role of complex 5 (ATP synthase)?
-catalyzes the synthesis of ATP from ADP and Pi in a reaction that is driven by the proton gradient generated during the ETC
what is the role of the F0 subunit of ATP synthase?
- embedded in the inner membrane
- contains the proton channel of the subunit
what is the role of the F1 subunit of ATP synthase?
- 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
how do the alpha and beta subunits of F1 work?
- each alpha subunit binds ATP but these nucleotides do not participate in any reactions
- beta subunits undergo conformational changes
what are the steps of the beta subunit conformational changes?
- **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
describe the flow of the beta subunits of ATP synthase
Open (release ATP, recruit ADP + Pi) –> loose (bind ADP + Pi) –> tight (catalyze formation of ATP) –> open
when does the interconversion of beta subunits occur?
the interconversion occurs when the gamma subunit use the energy associated with the proton gradient to turn, causing conformational changes in the beta subunits
how is ATP in the mitochondria transported to the cytoplasm?
- 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
which NADH molecules in eukaryotes have access to complex 1 of the ETC?
NADH in the mitochondrial matrix
what is the purpose of the glycerate phosphate shuttle?
allows electrons from NADH outside the matrix to enter the ETC through reduction of dihydroxyacetone
what is the purpose of the malate aspartate shuttle?
- 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
what is an unfortunate consequence of oxidative phosphorylation?
- the release of reactive oxygen species (toxic)
- superoxide radical
- hydroxyl radical
- hydrogen peroxide
what is the role of superoxide dismutase?
- converts superoxide to hydrogen peroxide
- hydrogen peroxide can then be converted to water and oxygen by catalase
what are some compounds that target any of the complexes I-IV in the ETC?
- carbon monoxide
- cyanide
- sodium azide
- rotenone
- antimycin A
- amytal
what is the result of inhibitors of the complexes of the ETC?
any compound that stops electron transport will stop respiration - you will stop breathing
what is a compound that targets the F0 subunit of ATP synthase?
oligomygin
what is the result of inhibitors of the F0 subunit of ATP synthase?
electron transport can be stopped by stopping ATP synthesis
what are some uncouplers that target the proton gradient?
- 2,4-dinitrophenol
- trifluoricarbonylcyanide phenylhydrazone
what is the result of the uncouplers of the proton gradient?
an uncoupler breaks the connection between the ETC and ATP synthesis - ETC happens without making any ATP
what is the mechanism of uncouplers?
- *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
