Electron transfer and oxidative phosphorylation Flashcards
What is stage 3 of catabolism
- electron transfer and oxidative phosphorylation
- occurs in mitochondria
- is oxidation or carbohydrates, lipids, amino acids with oxidation phosphorylation
- used to synthesise ATP
What happens when cofactors are oxidized
- called energetics
- direct oxidation of NADH and FADH2 by O2 releases large amounts of energy, enough to synthesize several moles of ATP
ΔG’= -nF ΔE’
NADH + H+ + 1/2O2 -> NAD+ +H2O
ΔE= 1.114 and ΔG= -220 kJ/mol
FADH2 + 1/2O2 -> FAD + H2O
ΔE= 1.04 and ΔG= -200 kJ/mol
*Reactions release a lot of energy, but not able to be collected in covlanet bond
What is the mitochondrial electron transport chain/ why is it necesairy
- reducing equivalents from reduced cofactors are passed to oxygen indirectly along the ETC
- instead of releasing all availbale neergy at once, the reoxidation of NADH and FADH2 by oxygen is broken up into several distinct processes with smaller free energy changes
How does the ETC work
- comprised of a special set of electron carriers aranged in order of increasing reduction potential
- the reducing equivalents are passed from molecule to molecule all the way up to oxygen, the terminal electron acceptor
- contians four unique enzymes (electron carrier complexes) that catalyze the transfer of electrons from one carrier to another
What is complex 1
NADH -> Q
uses NADH dehydrogenase
What is Complex II
FADH2 -> Q
using succinate dehydrogenase (also used in TCA)
What is complex III
Q -> Cyctochrome C
- enzyme: cytocrome c reductase
Why do NADH and FADH need different ways to egt into ETC
- one is soluble
- only specific FADH2 are able to enter ETC through complex II
What is complex IV
cytochrome C -> O2
enzyme: cytochrome oxidase
What is this
coenzyme Q
What is coenzyme Q
- also called uniquinone
- lipid soluble benzoquinone with a long isoprenoid tail (r)
- If accepts 1 election & 1 proton = Semiquinone radical *QH
If accepts 2 electrons & 2 protons to form alcohol= ubiquinol (QH2)
- this allows ubiquinone to function at junctions between two electron donors and one electron acceptors
- ubiquinol can freely move in membrane, carrying electrons from one ETC complex to another
* can be involved in 1 or 2 electron reductions
What is cytochrome C
- cytochroms= huge family of proteins with iron containing heme prosthetic groups
- cytochrome C, a soluble protein in mitochondrial intermembrane shuttles electrons from complex III of ETC to complex IV
- iron atom of heme acts as the redox active component and carries one electron at a time
*heme contains iron, is prosthetic group inside cytochrome c
Cytochrome C (Fe3+) + e- -> Cytochrome C (Fe2+)
Give an overview of the ETC
1: complexes I and II transfer electrons to Q and reducing it to QH2
2. QH2 passes electron to cytochrome c through complex III (both Q and cytochrome c are mobile electron carriers)
3. Complex IV tranfers electrons from reduced cytochrome c to O2
4. ELectron flow through complexes I, III, and IV is accompanied by proton flow from the matrix to the inner membrane space
* only ____ is i membrane* succinate?
What is the collector of reducing equivalents
CoQ
- NADH: Via complex 1
- Succinate dehydrogenase (FADH2) via complex II
- Acyl CoA dehydrogenase (FADH2) thorugh series of electron carriers
- Glycerol 3 phosphate shuttle dehydrogenase shuttle (FADH2)
How was the sequence of electron carriers determined?
- through sue of respiratory inhibitors acting at different points in chain
- in presence of an electron donor and O2 all carriers occuring before point of obstruction become reproduced and the carriers beyond the point become oxidized
- amny of the carriers have distinct optical chromophores with different optical spectra under oxidized and reduced states
- inhibit enzymes at different points, see what is reduced and what is oxidized and cna determine sequence
What is the outcome of the ETC
- each pair fo electrons transfered from NADH to O2
- four protons are pumped by complex 1
- four protons by complex III
- and 2 by complex IV
- TOTAL =10 protons
- electrons form FADH2 bypass complex I
- total number of protons =6 per each FADH2 oxidized
- Outcome=proton gradient across inner mitochondrial membrane which acts as a temporary reservoir
- energy stored in gradient is called proton motive force
What are the two components fo the proton motive force
- Chemical potential energy: due to difference in concentration of H+
- Electrical potential energy: due to separation of charges
How is the concentration of protons transormed into ATP
- chemiosmotic theory (peter mitchell)
- free energy liberated by redox reaction is sued by ETC to pump protons moving H+ from matrix to inner membrane space
- energy is stored as an electrochemical gradient (proton motive force)
- as protons flow back into mitochondrial matric down its concentration gradient, energy of electrochemical gradient is released and used for generation of ATP by ATP synthase enzyme (channel for protons to come down, releasing energy used to synthesize ATP from ADP and P)
What happens if there is an inhibitor of electron transfer
- neither reaction occurs without the other
- the chemiosmotic theory can readily explain this obligatory coupling
- An inhibitor of electron transfer wil inhibit both the ocygen consumption and the ATP synthesis
- since energy for ATP synthesis is derived from oxidation process, ibhibition of electron transfer by various inhibitor will invariably inibit ATP synthesis
What happens if there is inhibition of ATP synthase
- also blocks the elctron transport chain, they are linked
- when ATP synthase is blocked the protons that are pumped remain in the inter membrane space and build up to a very high concentration
- the energy required to pump protons against this gradient will eventually exceed the energy available from NADH oxidation
- proton translocation is an obligatory part of the catalytic cycle of electron transport chain complexes, so if they can no longer pump protons, they no longer perform electron transport
*be able to explain couples through chemiosmotic theory
What inhibits ATP synthase
- venturicidin or oligomycin
Why are they coupled
- as soon as ATP synthase is inhibited ETC stops
- ATP synthase depends on NAD of rpoton gradient created by ETC, if ATP stoped no proton gradient there is no energy for ATP synthase
- if ATP synthase is inhibited protons are no longer able to come down gradient into matrix, channel is blocked. protons are pumped and gradient builds, complexes do not have enough energy to pump into inner membrane space, pumpm stops too
*if cant pump protons cannot carry out oxidation processes
*relook over be able to explain how eahc process depends on each other
Explain uncoupling of oxidative phosphorylation
- if the integrety of the inner mitochondiral membrane is disrupted, then the proton gradient is eliminated: electron transport continues: ATP synthesis stops
- this system uncoupled (coupler), provides an alternate route for protons to come down gradeint, no longer dependent on ATP synthase
- Dinitrophenol (DNP) is the classec example of a chemical uncoupler
*DNP does not disrupt the integrity of the membrane, It just has similar effect to that (be able to explain)*
- When DNP is added to the mitochondria, ATP production ceases but ETC continutes
Explain the action of 2,4 DNP
- acts as a ionophore, ion carrier
- Dinitrophenolate anion (DNP-) initially doprotonated, it picks up a proton to form DNPH and transports it across the IMM
- it will release the H+ in the matrix forming DNP-
- DNP- will cross back to the inner membrane since its negative charge is delocalized over the aromatic ring and structure retains considerable hydrophobicity
*this is the altnernate route protons take*
- proton gradient is collapsed and synthesis of ATP stops
- DNP brings protons into the matrix, so no ATP isnt synthsized, energy of the proton gradient is not conservated by ATP formation so it disspiates as heat
What does CN- do
inhibits complex IV
What does CO do
inhibits complex IV
What does antimycin A do
Inhibits complex III
What does Rotenone, barbituarates do
inhibits complex 1
