2. (33 pts total) Oxidative Phosphorylation and ATP Synthesis a. (8 points) Cyan
ID: 713245 • Letter: 2
Question
2. (33 pts total) Oxidative Phosphorylation and ATP Synthesis a. (8 points) Cyanide and the antibiotic oligomycin B both inhibit mitochondrial oxidative phosphorylation when the reaction substrate is either malate or succinate. Describe how the uncoupler dinitrophenol (DNP) could be utilized to determine whether either of these molecules is a direct inhibitor of ATP Synthase mam oranoud de to reihaste theetrns fort dain lautarp Synthesis-mudA-hll be-blacle adue to direct i^h hon. TF dhe inhewhs-blocked Complex , then the achtons of the DNPExplanation / Answer
Ans. Cyanide as ETC Inhibitor: Cyanide (CN-) binds to Fe-atom of cytochrome a3 component of cytochrome c oxidase complex (complex IV of ETC). Thus, it blocks the flow of electrons through it. Moreover, due to permanently retaining the electron in it instead of passing it to O2 (the terminal electron acceptor), complex IV FREEZES in its reduced state.
Once cyt C oxidase is blocked, the Coenzyme Q- cytochrome C oxidoreductase (complex III of ETC) can’t pass electrons to complex IV (already frozen in reduced state) and in turn gets “frozen” in its reduced state, too. Subsequent inhibition of electron flow from complex III also freezes complex I and II in their respective reduced states.
The ETC complexes frozen in their reduced states can’t oxidize NADH and FADH2, so can NOT pump protons from mitochondrial matrix (MM) to inter membrane space (IMS). Therefore, building up of electrochemical gradient across the inner mitochondrial membrane (IMM) is inhibited, too.
# DNP is an uncoupler that uncouples electrochemical gradient in form of H+ from oxidative phosphorylation.
Since all the ETC complexes are FROZEN in their reduced state, uncoupling proton gradient from oxidative phosphorylation can’t re-initiate the flow of electrons UNTIL complex IV initiates electron flow through it by donating it’s electron to O2. Once complex IV is free of inhibitor, the unhindered electron flow starts, thus leading to re-initiation of ETC once again.
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