1. The P/O ratio formitochondrial oxidative phosphorylation is the number of ATPmolecules that are synthesized for each two electrons that enterthe electron transport pathway. Under normal conditions, the P/Oratio is approximately 2.5. [The derivation of this number will beexplained in class, though it is not necessary for you tounderstand the derivation to answer this question. Just know thatthe P/O ratio is the number of ATPs made for each NADH that isoxidized]. (a) Uncouplers cause the mitochondrial membrane tobecome permeable to protons, and so uncouple ATP synthesis fromelectron transport. What would be the effect of a low concentrationof an uncoupler on the P/O ratio? Note that a low concentration ofuncoupler will only partially dissipate the proton gradient. (b)DCCD is a reagent that inhibits ATP synthase by blocking the protonchannel through the enzyme. What effect would DCCD have on the P/Oratio? Tip: it is important to understand that inhibition of ATPsynthase also inhibits electron transport, because an increase in[H+] in the inter-membrane space exerts an inhibitorybackpressure on the proton pumping complexes (ie rememberthat ATP synthesis and electron transport are coupledprocesses). (c) If mitochondria are inhibited with DCCD, and thenan uncoupler is added, what will be the effect of the uncoupler onATP synthesis, oxygen consumption and the P/O ratio? Explain yourreasoning behind all answers.
1. The P/O ratio formitochondrial oxidative phosphorylation is the number of ATPmolecules that are synthesized for each two electrons that enterthe electron transport pathway. Under normal conditions, the P/Oratio is approximately 2.5. [The derivation of this number will beexplained in class, though it is not necessary for you tounderstand the derivation to answer this question. Just know thatthe P/O ratio is the number of ATPs made for each NADH that isoxidized]. (a) Uncouplers cause the mitochondrial membrane tobecome permeable to protons, and so uncouple ATP synthesis fromelectron transport. What would be the effect of a low concentrationof an uncoupler on the P/O ratio? Note that a low concentration ofuncoupler will only partially dissipate the proton gradient. (b)DCCD is a reagent that inhibits ATP synthase by blocking the protonchannel through the enzyme. What effect would DCCD have on the P/Oratio? Tip: it is important to understand that inhibition of ATPsynthase also inhibits electron transport, because an increase in[H+] in the inter-membrane space exerts an inhibitorybackpressure on the proton pumping complexes (ie rememberthat ATP synthesis and electron transport are coupledprocesses). (c) If mitochondria are inhibited with DCCD, and thenan uncoupler is added, what will be the effect of the uncoupler onATP synthesis, oxygen consumption and the P/O ratio? Explain yourreasoning behind all answers.
