WEEK 2: ETS & Oxidative phosphorylation Flashcards
how do NADH and FADH2 give free energy to the ETS?
NADH and FADH2 contain energy obtained from catabolism – they get re-oxidised by transferring electrons to components of the mitochondrial Electron Transport System (ETS)
how is the energy produced in the ETS used?
ATP formation
what is the final electron acceptor from the ETS? What is produced?
O2
H2O produced
what is a reducing agent?
a substance that donates electrons
what is an oxidising agent?
a substance that receives electrons
what is the redox equation between redox pairs NADH and O2?
1/2O2 + NADH + H+ —> H2O + NAD+
describe REDOX POTENTIALS AND FREE ENERGY in ETS.
- In the ETS, electrons are passed from one redox pair to the next –eventually to O2
- The acceptor must have a more positive redox potential than the donor
where are enzymes of the ETS and ATP synthase found?
in the inner mitochondrial membrane
how is a chemical gradient established in mitochondria?
Inner membrane cristae (folds) increase membrane surface area and its impermeability allows the establishment of chemical gradients
what is the function of the ETS?
ETS – function is to regenerate NAD+ and FAD, with the free energy released used to generate ATP, and with the reduction of oxygen to water
what does FAD do?
transfers electrons as hydrogen atoms
what is the role of coenzyme Q in the ETC?
Acts as a link between Complex I or II and Complex III
describe the ETS sequence
NADH -> Complex I -> Complex II -> CoQ -> Complex III -> Cyt C -> Complex IV -> O2
how is e- transferred from complex 1 to CoQ?
Contains 6-7 Fe-S clusters through which e- are carried in a zig-zag pattern and transferred to CoQ
give the function of complex 1
Functions to oxidize NADH and reduce Coenzyme Q
give the function of complex 2
Functions to oxidize succinate via the generation of FADH2.
Reduces Coenzyme Q.
why doesn’t complex 2 pump H+ across membrane?
not enough energy to pump H+ across the membrane, also not a membrane spanning complex, like complex I, so cannot act as a proton pump
give the function of complex 3
Functions to oxidize Coenzyme Q and reduce Cytochrome c
give the function of complex 4
Functions to oxidize cytochrome c and reduce oxygen to water. Again is a large membrane spanning complex that contains binding sites for cytochrome c and molecular oxygen
which complexes donate electrons to complex 5?
complex 1,3,4
How much ATP is produced through oxidative phosphorylation?
Approximately 2.5 ATP for each NADH reoxidised and 1.5ATP for each FADH2 reoxidised
How does the NADH produced in glycolysis get reoxidised under aerobic conditions?
It gets reoxidised by components of the glycerol-3-phosphate shuttle or the aspartate-malate shuttle system
why are shuttles needed for NADH in aerobic conditions?
NADH produced in cytosol has to be reoxidised
describe the cycle of the glycerol 3-phosphate shuttle.
- NADH must be reoxidised to NAD+
- dihydroxyacetone phosphate reacts with NADH to produce glycerol 3-phosphate and NAD+
- glycerol 3-phosphate reoxidises FAD to “reproduce” dihydroxyacetone phosphate and FADH2
- FADH2 then transfers e- to CoQ
what is the ATP yield when a glycerol 3-phosphate shuttle operates (which is in most tissues)?
ATP yield = 1.5
NADH cytosol
FADH2 mitochondrion
describe the cycle of the aspartate-malate shuttle.
ppppppp
how ,many protons are pumped through complex 1, 3 and 4 per cycle?
complex 1 - 4
complex 3 - 4
complex 4 - 2
what is proton motive force?
the force that promotes movement of protons across membranes downhill the electrochemical potential that wishes to re-establish equilibrium.
what does the chemostatic mechanism involve?
the storage of energy in the form of a proton gradient, which is then used to facilitate the phosphorlyation of ADP to ATP by the ATP snythase complex.
what is uncoupling?
it occurs when H+ re-enter the mitochondrial matrix without going through ATP synthase.
can be brought about by chemicals or physiologically by uncoupling proteins
what does uncoupling result in?
increased O2 consumption and release of energy as heat
IMPORTANT
name 3 chemical uncouplers.
2,4-Dinitrophenol
Valinomycin
Gramicidin A
what is 2,4-DInitrophenol? How does it work?
A chemical uncoupler.
It crosses the inner mitochondrial membrane and releases protons in the matrix - reduces proton gradient
how does valinomycin work?
a chemical uncoupler that is an antibiotic that makes the inner MM permeable to K+ and dissipates the membrane potential
how does gramicidin A work?
a chemical uncoupler that is a channel forming drug - makes the inter MM permeable to protons and reduces the proton gradient
why are physiological uncouplers most likely to be used?
an organ need to generate more heat for thermal regulation
which uncoupling protein contributes to thermal regulation?
UCP1 - thermogenin expressed in brown adipose tissue
what do uncoupling proteins (UPC) do?
form channels through the inner membrane which conduct H+ back into the matrix
what are the 5 UPCs? Where are they expressed?
UCP1 - in brown adipose tissue
UCP2 - most cells
UCP3 - skeletal muscle mainly
UCP4 and 5 - brain
how do inhibitors of the ETS work?
inhibitors are poisons!!
Inhibits electron flow, proton pumping and reducting of ATP synthesis.
how does absence of O2 result in inhibition of ETS?
no terminal acceptor
how does iron deficiency result in inhibition of the ETS?
no iron for cytochromes or Fe-S
regarding ADP and ATP, describe the resting state.
ADP is low and ATP conc is high - no need for ETC so low O2 consumption
describe the activity state regarding ATP and ADP.
ADP conc is high and ATP conc is low - switch on ETC and increase O2 consumption
how does ATP, ADP and Pi transport through outer membrane?
via voltage dependent anion channels (VDACs)
what is the FINAL general equation for the overall aerobic breakown of glucose?
glucose + 6O2 = 30ADP + 30Pi —> 6CO2 +6H2O + 30ATP
what is the FINAL general equation for the overall anaerobic breakown of glucose?
glucose + 2ADP + 2Pi —> 2lactate + 2ATP
