Oxidative Phosphorylation Flashcards
What fuels ATP synthesis?
NADH and FADH2 bioenergy electron transfer to respiratory chain fuels ATP synthesis in mitochondria
What occurs in the Electron Transport Chain?
Oxidation of reduced coenzymes NADH and FADH2
Pumping of protons (H+)
Synthesis of ATP
Occurs in mitochondria
What is present in the diff parts of the mitochondria with regards to ETC?
Outer membrane - freely permeable to small molecules and ions
Inner membrane - impermeable to most small molecules and ions including H+
-Contains: respiratory electron carrieris (complexes I-IV), ADP-ATP translocase, ATP synthase (F0F1), other membrane transporters
Matrix - contains pyruvate dehydrogenase xomplex, citric acid cycle enzymes, fatty acid ß-oxidation enzymes, amino acid oxidation enzymes, DNA, ribosomes, many other enzymes, ATP, ADP, P, Mg2+, Ca2+, K+
Overview of what happens in oxidative phosphorylation?
Involves proteins and electron carriers that are part of the inner mitochondrial membrane
-Electrons from reduced coenzymes are removed and passed along a series of membrane-bound carriers
-The movement of electrons is a sequence of REDOX reactions
-The redox reactions are exergonic - the free energy made available by the reactions is used to punmp protons (H+) to the intermembrane space to establish a potential gradient
-Mkaing ATP rectifies the deficit in gradient by providing a channel through which the protons can pass back out into the matrix
How many protein complexes are involved in the ETC and where are they?
5 protein complexes
Located on inner mitochondrial membrane
How is ATP made by oxidative phosphorylation?
-Cells úse the energy from a flow of electrons through 4 protein complexes (respiratory chain) to pump H+ ions across a membrane
-The energy of the H+ gradient is harnessed to make ATP
-This is done in the presence of oxygen
What are I-IV enzyme complexes?
i NADH dehydrogenase
ii Succinate dehydrogenase
iii Ubiquinone cytochrome c oxidoreductase
iv Cytochrome oxidase
What is oxidative phosphorylation?
The process of ATP formation due to electron transfer from NADH/FADH2 to O2
-all catabolism in presence of O2 converges to oxidative phosphorylation
-in euks, occurs in inner mitochondrial membrane where respiratory electron carrier proteins and ATP synthase reside
What is the PMF?
Proton Motive Force
-energy of electron transfer efficiently conserved in proton gradient
-creates electrical potential - inside membrane negatuve and outside membrane positive
What is ATP synthesis driven by?
-PMF proton flow back to matrix through ATP-synthase complex - Complex V
What are the 3 types of electron transfer?
-Direct transfer as electrons
-Transfer as hydrogen atom
-Transfer as hydride ion
What is the term reducing equivalent used to describe?
A single elctron equivalent transferred in oxidation reduction reaction
What are the major electron carriers in the process?
-NAD, FAD, FMN
-Ubiquinone
-Iron-Sulfur proteins
-Cytochromes
(iron-sulphur and cytochromes are 2 diff forms of iron containing proteins)
Structure of Ubiquinone? How is it reduced/oxidised?
-Also called coenzyme Q or Q lipid
-Benzene type structure with long isoprenoid side chain
-Quinione ring structure can accept 1 or 2 electrons in hydrogen
-So is reduced from Q to QH to QH2
-Can be oxidised to donate these electrons
What are cytochromes?
-Proteins with iron containing heme prosthetic groups
-Different classes a, b, c
-4 N atoms coordinate to central iron
-The iron donates/accepts electrons; reduced/ oxidised; Fe2+/Fe
-a and b and some of c cclass part of integral membrane proteins but one form ogf cyt c is freely diffusible and soluble
What are Iron-sulphur proteins?
-iron complexed with sulphur
-S atoms in Cys residues of proteins - simple to complex structures
-As in cytochromes, the iron can be oxidised and reduced - one elctron transfer
-Atleast 8 of these work in the ETC
Electron carrier sequence?
NADH
Flavoprotein
Ubiquinone
Fe-S centres
Cytochromes
Finally O2
How is the sequence of the electron carriers determined?
By use of inhibitors that can block electron transport between the carriers
What are electrons carried by to complete oxidative phosphorylation?
Electrons are carried via electron carriers in supramolecular enzyme complexes embedded in inner mitochondrial membrane
-Complex I-IV - together known as respiratory chain
-Also contains mobile electron carriers unbiquinone and Cytochrome C
Where is the respiratory chain found?
Inner membrane of mitochondria - within cristae
What is and what does Complex I do?
NADH dehydrogenase
-very large with 45 diff polypeptide chains
-transfers 2 electrons from NADH to ubiquinone (Q)
NADH -> NAD+ + Q -> QH2
-4 protons H+ pumped across matrix –> intermembrane space
What is and what does Complex II do?
Succinate Dehydrogenase
-also part of citric acid cycle
-transfers electrons from succinate -> FADH2 -> ubiquinone
so electrons pass from succinate ->FAD -> FADH2 -> FAD+ + Q-> QH2
What is and what does Complex III do?
Ubiquinone Cytochrome C oxidoreductase performs very complex electron transfer= Q cycle
1. end result is UQH2 transfers 2 electrons to two Cytochrome C
2. Electron trasnfer drives expulsion of 4 more prtons from matrix to intermembrane space
What is and what does Complex IV do?
Cytochrome Oxidase
-Transfers electrons from cytochrome C to O2 - complete electron transfer
-Electrons trnsferred from Cyt C -> Cyt a -> Cyt a3 -> O2
1. carries out 4 electron reduction of O2 to H2O
2. 2 protons transferred from matrix to intermembrane space
Inhibitors that block electron transport from electron carriers?
-Rotenonne blocks b/w Complex I and Q
-Antimycin blocks b/w Complex III and IV
-Cyanide blocks b/w Complex IV and O2
What does each NADH that donates electrons to respiratory chain drive the expulsion of?
4H+ through complex I and III and 2H+ through complex IV
-10 H+ travel to intermembrane space
What does each FADH2 that donates electrons to respiratory chain drive the expulsion of?
4H+ through complex III and 2H+ through complex IV
-6 H+ travel to intermembrane space
(Electron transfer creates PMF - inside membrane matrix is negative and outside membrane matrix is positive)
What are other sources of FADH2
-FADH2 is not just produced by the succinate dehydrogenase rxn succinate to fumarate
-Also produced from 1st rxn in fatty acid oxidation catalysed by Acyl-CoA dehydrogenase
-Donates electrons from FADH2 to ETF (electron transfer flavoprotein) which donates electrons to ubiquinone
What did Peter Mitchell propose?
The chemiosmotic model
-PMF conserves energy of electron transfer and drives ATP synthesis as protons flow back into mitochondrial matrix via a proton pore F0 in inner mitochondrial membrane
-F0 is part of ATP synthase enzyme
What did his experiments show?
-Electron transfer, PMF and ATP synthesis are obligately coupled
-Inhibitors of electron transport block ATP synthesis
-Inhibitors of ATP synthesis block electron transport
What did John Walker get a Nobel prize for in 1977?
-Working out how PMF causes enzyme ATP synthase to synthesise ATP
-‘the ATP synthase complexes in mitochondria make the ATP required to sustain life by rotary mechanism’
-ATP synthase enzyme = F-type ATPase purified and crystallised has 2 distinct functional domains F1 and F0
-human ATP synthase aasmbled from 27 nuclear encoded genes and 2 mitochondrially encoded genes
What is F1?
-Peripheral membrane protein
-Attached to inner mitochondrial membrane -N side
-Catalytic domain that synthesizes ATP
What is F0?
-integral membrane protein
-spans mitochondrial inner membrane
-proton pore
-H+ move through it againts conc gradient from intermembrane space through F1 to matrix
-Proton flow enables ATP synthesis
F1 structure?
-9 subunits - 5 diff types
-composition - alpha 3 ß 3 y delta e
-alternating alpha and ßs surround central y shaft
-alpha and beta subunits have nucleotide binding sites
-ß subunits more important role can bind ADP, ATP or be empty
F0 structure?
-Integral membrane protein
-makes up proton pore
-composed of 3 subunits a b2 cn
-C subunits cyclinder-like structure with pore - number of C subunits differs b/w species 8-15
-C subunits rotate together around perpendicular axis - around e and y which standon C subunits
What did Paul Boyer do?
-Proposed the binding change mechanism to explain how ATP synthase synthesises ATP
-protons pass through F0 and cause cylinder of c units attached to y - subunit of F1 to rotate about long axis of y
-y-subunit rotates and passes through centre of alpha3 ß3 which are stationary
-rotational catalysis causes ATP synthesis
