This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory chain, Subject name: Biochemistry
[{'content': 'Various compounds are added to mitochondria having a tightly coupled oxidative phosphorylation system. Addition of which of the following substrates will generate the LEAST amount of ATP \nSelect and explain. \nA. Malate, B. Succinate, C. Malate with rotenone, D. Succinate with rotenone', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Rotenone is a site-specific inhibitor of electron transpo. it acts at the level of complex I. Malate feeds electrons to reduced nicotinamide adenine dinucleotide (NADH), which in turn is passed into the electron transpo system at the level of complex I, through NADH dehydrogenase just before the blockage induced by this drug. Therefore, no electrons can be transpoed from NADH and no adenosine triphosphates (ATPs) are made. Succinate feeds in electrons from the reduced form of flavin adenine dinucleotide (FADH2) at the level of complex II, through the action of succinyl dehydrogenase. Complex II passes its electrons to coenzyme Q at a point beyond the site of rotenone inhibition; therefore, rotenone has no inhibitory effect and 2 ATPs are produced per atom of oxygen consumed. (The number of ATPs produced per atom of oxygen used is often expressed as the number of phosphate ions taken up divided by the atoms of oxygen used. This is called the P/O ratio.) in the absence of any inhibitor, the P/O ratio for malate is 3 and for succinate 2. Actinomycin D is an inhibitor of DNA synthesis, not oxidative phosphorylation. The inhibitor of electron transpo is actinomycin A. Ref : Biochemistry by U. Satyanarayana 3rd edition Pgno :256', 'role': 'assistant'}]