This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: vitamins, Subject name: Biochemistry
[{'content': 'Menadione is analog of? \nSelect and explain. \nA. Vitamin K, B. Vitamin A, C. Vitamin D, D. Vitamin C', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The principal role of vitamin K is in the posttranslational modification of various blood clotting factors, in which it serves as a coenzyme in the carboxylation of ceain glutamic acid residues present in these proteins.Vitamin K exists in several forms, for example, in plants as phylloquinone (or vitamin K1), and in intestinal bacterial flora as menaquinone (or vitamin K2). A synthetic form of vitamin K, menadione, is availableReference: Lippincott edition 5; page no: 389', 'role': 'assistant'}]