This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Which component transfers four protonsa) NADH-Q oxidoreductaseb) Cytochrome-C oxidasec) Cytochrome C - Q oxidoreductased) Isocitrate dehydrogenasee) Succinate Q reductase 
Select and explain. 
A. ac, B. bc, C. ad, D. b
A: ac
Answer: A: ac 
Explanation: NADH-Q oxidoreductase & 'c' i.e., Cytochrome C - Q oxidoredictase

Complex I (NADH-CoQ reductase) and complex in (CoQ - cytochrome c reductase) pump 4 protons each and complex IV (cytochrome c oxidase) pumps 2 protons.