Metabolic Poisons Flashcards
Describe the relationship between the demand and the supply of energy
There is a direct relationship between the supply of utilisable energy in the form of ATP and the demand for energy use at any one time. ATP is not made unless it is required to drive another process.
Why is mitochondrial respiration dependent on ADP
This relates to the physio-chemical coupling of the mitochondria. In other words, as substrates move along the ETC each component uses the energy released in the ETC to transport H+ ions across the inner mitochondrial membrane, so the concentration of H+ is higher on the other side of the membrane. The electrochemical gradient of H+ represents a temporary store of energy that is used by ATP synthase to phosphorylate ADP to ATP, the H+ flowing back across the membrane in the process.
This metabolic coupling of the ETC and oxidative phosphorylation ensues that substrates are only metabolised when there is demand for ATP, and thus O2 consumption only occurs at the end of the chain if there is the presence of substrate and ADP.
Why is the rate of respiration in the presence of succinate and ADP greater than with glutamate plus malate and ADP
NADH- linked substrates such as malate feed electrons into the ETC via the NADH dehydrogenase complex (complex 1) and so can generate 3 ATP for each oxygen atom reduced to water. in contrast, oxidation of succinate feeds into the chain via FADH2 and succinate dehydrogenase (complex 2) thus utilising only two of the phosphorylation sites. So, to generate a given quantity of ATP, more succinate must be oxidises than malate and glutamate and hence more O2 used at a faster rate.
What does the malate-aspartate shuttle remove
Excess oxaloacetate from the mitochondrial matrix.
Describe the action of the malate-aspartate shuttle in vivo
In vivo malate and glutamate are required for the malate-aspartate shuttle: the principal mechanism for the movement of reducing equivalents (the NADH produced during glycolysis) from the cytoplasm into the mitochondrial matrix. The oxaloacetate concentration in mitochondria in vivo is exceedingly low (0.1microM) whereas malate concentration is about 10mM, due to the unfavourable reaction carried out by malate dehydrogenase.
Why is it necessary to add simultaneously glutamate and malate as NADH-linked substrates
in experiments involving isolated mitochondria the addition of malate alone causes the build-up of oxaloacetate, which would inhibit the malate dehydrogenase and therefore the production of NADH (the electron source for respiratory transport). However, the further addition of glutamate allows the excessive oxaloacetate to be removed from the mitochondrial matrix via the malate/aspartate shuttle and therefore the production of NADH to continue while malate is available. Moreover, an active malate/aspartate shuttle allows for alpha-ketoglutarate to be produced in the mitochondrial matrix making it available for its exchange for malate in the malate/alpha-ketoglutarate antiporter, allowing a constant flow of malate into the mitochondria.
How does glutamate allow for the removal of excess oxaloacetate
Oxaloacetate is converted into aspartate, which is exchanged for glutamate.
Glutamate IN, Aspartate OUT.
What happens when KCN is added
By reacting covalently with Fe3+ in cytochrome oxidase, the respiratory poison KCN inhibits the terminal step in the ETC (complex 3), so respiration ceases.
What is oligomycin
An antibiotic produced by fungi.
Under normal circumstances, what would happen after addition of oligomycin
Oligomycin interferes with and hence reduces the ability of ATP synthase to utilise the H+ electrochemical gradient. So, in coupled mitochondria, oligomycin would be expected to inhibit respiration. Oligomycin only inhibits ‘Coupled’ mitochondria.
Why is oligomycin without effect in coupled mitochondria
Oligomycin is without effect when the prior addition of DNOC has uncoupled the mitochondria. In other words the Kreb’s cycle and oxidative phosphorylation are running maximally but the link to the generation of ATP is broken so the free energy released from the substrates is lost as heat, Consistent with this is the large increase in mitochondrial O2 consumption following the addition of DNOC. Membrane is already decoupled.
Describe how aromatic weak acids, such as DNOC pass through the mitochondrial membrane.
Aromatic weak acids such as DNOC and dinitrophenol are thought to pass readily through across the mitochondrial inner membrane in their undissociated from thus dissipating the electrochemical gradient.
Explain how DNOC dissipates the electrochemical gradient.
Outside DNOC- + H+ --- DNOC-H Inside DNOC-H --- DNOC- + H+ Build up of H+ where we need a low H+ concentration, flowback of H+ becomes less favourable, thus slower movement of H+ ions and slower generation of ATP.
When else does O2 consumption increase
Also tends to increase as cells die.
Why were respiration rate and body temperature rate elevate
DNOC acts as a pesticide by uncoupling mitochondrial respiration in insects so that their ETC runs uncontrollably and unproductively. The same happens in humans. Large amounts of metabolic fuels are consumed with the energy being wasted as heat, burn fat to release energy- fat stores deplete.
