This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Carbohydrates, Subject name: Biochemistry
All of the following steps act as sources of energy in citric acid cycle except - 
Select and explain. 
A. Citrate synthase, B. Isocitrate dehydrogenase, C. Succinyl thiokinase, D. Succinate dehydrogenase
A: Citrate synthase
Answer: A: Citrate synthase 
Explanation: Ans. is 'a' i.e., Citrate synthase* The total number of ATPs obtained in citric acid cycle is 10.S.NOENZYMEREDUCING EQUIVALENTATP EQUIVALENT1Isocitrate dehydrogenase1NADH2.52a ketoglutarate dehydrogenase1 NADH2.53Succinyl CoAATP/GTP14Succinate dehydrogenaseFADH21.55Malate dehydrogenaseNADH2.5Total 10* Hence citric acid cycle uses NAD, FAD, ADP and GDP. It does not use NADP as its coenzyme