9 - Metabolism 3 - oxidative phosphorylation Flashcards
how many electrons are produced in the reactions of glycolysis, pyruvate dehydrogenase complex, and the TCA cycle?
10 NADH
10 H+
2 FADH2
= each with 2 high energy electrons so total = 44
what are electrons from NADH and FADH2 used for?
to reduce O2 and H2O = their energy is used to pump protons (H+) from mitochondrial matrix into intermembrane space
what is pH environment comparison of intermembrane space & matrix?
pH decreased (acidic) in intermembrane space and increase in matrix
so protons flow back across the membrane following concentration gradient
energy of proton flow is used to phosphorylate ADP to ATP
how doe NADH from cytoplasm get in?
with malate-aspartate shuttle
as NADH can’t directly cross inner mitochondrial membrane & can’t be re-oxidised to NAD+ directly using electron transport chain
why is malate-aspartate shuttle important?
allows NADH into matrix - if no shuttle then metabolism would be uncoupled (glycolysis and oxidative phosphorylation separate)
how does malate-aspartate shuttle work? (the malate part)
*so the last step in TCA cycle malate is converted to oxaloacetate and at the same time NAD+ makes NADH + H+
- this reaction can be reversed as well
- so in the intermembrane space the NADH that was made in glycolysis can be used to generate oxaloacetate to malate
- the malate-aspartate shuttle can then transfer malate to mitochondrial matrix
- the malate can then make conversion to oxaloacetate in TCA cycle which generate NADH in addition to malate that arises from fumarate
what is the aspartate part of the malate-aspartate shuttle?
when the malate has been converted to oxaloacetate in matrix - some oxaloacetate used for TCA cycle, some of it is converted to aspartate (at the same time glutamate converted to alpha-ketoglutarate) and then the aspartate is taken through aspartate shuttle to cytosol where it can undergo reverse of reaction again to continue cycle of malate-aspartate shuttle
what is the point of cycling of malate-aspartate shuttle?
to maintain redox balance between cytosol and mitchondria
what is the electron transfer potential of NADH+ and FADH2 converted into?
the phosphoryl transfer potential of ATP
what is phosphoryl transfer potential of ATP measured in?
measured by the free energy change, delta Go’, for the hydrolysis of ATP
what is Electron transfer potential measured by?
the redox potential (or reduction potential), E’o, of a compound
what is the standard redox potential E’o of a reduced substance X?
a measure for how readily X donates an electron (in comparison with H2)
what does a negative and positive redox potential mean?
negative E’o = reduced form of X has a lower affinity for electrons than H2 (less likely to gain electrons)
positive means the opposite = higher affinity for electrons than H2 (more likely to gain electrons)
what is the standard free energy change proportional to?
the change in standard redox potential and the number of electrons transferred
what is the strongest of all terminal electron acceptors?
oxygen
what makes up the respiratory chain?
group of proteins that site together
= complex 1,2,3,4
how does respiratory chain start?
NADH donates a pair of electrons and the electrons allow complex 1 to pump protons (H+) from intracellular matrix intermembrane space
what is complex 2 of respiratory chain? i.e. what does it couple as?
succinate dehydrogenase (which catalyses step 6 succinate - fumurate in TCA cycle)
= so electrons from FADH2
and also part of TCA cycle
what are the proteins in respiratory chain linked by?
cytochrome C = takes electrons donated to complex 3 and links them to complex 4
what are between complexes in respiratory chain?
electron carriers - ubiquinone, Q reductase & cytochrome C
where do electrons from
a) NADH enter?
b) FADH2 enter?
a) at complex 1
b) at complex 2
where are electrons ultimately transferred to in respiratory chain?
onto O2 to form H2O
why are electrons handed to carriers in respiratory chain - why do they keep moving?
because they move to carriers with increasingly positive (oxidising) redox potentials
describe the electrochemical gradient of mitochondria?
- more protons in intermembrane space than in matrix (due to being pumped out by complex 1,3,4)
- Forms an electrical field with the matrix side more negative
- Protons ‘want’ to flow back into the matrix
- Flow back into the matrix is coupled to ATP synthase which phosphorylates ADP +Pi -> ATP
what is process of electron transport chain?
NADH passes electrons to complex 1 and FADH2 passes electrons to complex 2
- electrons from both complex 1 & 2 go to ubiquinone which pass electrons to cytochromes and to complex 3 then cytochrome C then complex 4 which transfers to O2 and makes H2O
what can inhibit oxidative phosphorylation?
- carbon monoxide outcompetes oxygen (better at binding to haem groups so stops process of oxygen carriage and oxidative phosphorylation)
- cyanide & azide does the same
= they inhibit the transfer of electrons to O2 so no proton gradient formed and no ATP synthesised
what is an example of uncoupling proteins?
thermogin in brown adipose tissue = brown adipose tissue contains a high number of mitochondria and is rich in uncoupling protein 1 (UCP1). UCP1 allows the uncoupling of oxidative phosphorylation from ATP synthesis, leading to the generation of heat without the production of ATP
non shivering thermogenesis - maintains body temp in newborns, hibernating animals cold-adapted mammals (so maintains temp when unable to shiver)
what is uncoupling and what is the effect?
uncoupling = breaks the link between electron transport chain and ATP synthase (by inserting own protein channels - ionophores)
this means electrons bypass ATP synthase so protons go back into matrix instead so no proton gradient and no ADP→ ATP.
electrons still flow through complexes until end so oxygen keeps being delivered to tissue = as ADP rise, body increases metabolic rate to try increase NADH and FADH2 but useless →this all means more energy available to turn into heat energy
what is P/O ratio?
- A measurement of the coupling of ATP synthesis to electron transport
- Number of molecules of inorganic phosphate (Pi) incorporate into ATP per atom of oxygen used
- Depends on the substrate which is oxidised
what is P/O ratio of
a) NADH
b) FADH2
a) 1 NADH -> 3 ATP (as 3 proton pumps - 1,3,4)
b) 1 FADH2 -> 2 ATP (as only 2 proton pumps since skips complex 1 - proton pump 3,4 only)
how many ATP does 1 glucose yield?
30-32 ATP (depends on precise values of P/O)
