This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General, Subject name: Physiology
[{'content': 'Which of the following in not a second messenger- \nSelect and explain. \nA. cAMP, B. NO, C. CO, D. Protein kinase', 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. is 'd' i.e., Protein kinase * Second messengers are molecules that relay signals from the membrane receptors to target molecules inside the cells. In above described receptors second messengers are cAMP, cGMP, Phosphatidylinositol, diacylgleceral, IP3, Ca+2.* Some gaseous molecule can diffuse both through cytosol and across cellular membranes and act as second messenger. These are nitric oxide (NO), Carbon monoxide (CO) and hydrogen sulphate (H2S).", 'role': 'assistant'}]