This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of nucleic acids, Subject name: Biochemistry
Polyamine Ike putrescine is derived from 
Select and explain. 
A. Arginine, B. Ornithine, C. Yohimibine, D. Arginosuccine
B: Ornithine
Answer: B: Ornithine 
Explanation: The enzyme ornithine decarboxylase (ODC) catalyzes the decarboxylation of ornithine (a product of the urea cycle) to form putrescine. This reaction is the committed step in polyamine synthesis. In humans, this protein has 461 amino acids and forms a homodimer.Ref: https://en.wikipedia.org/wiki/Ornithine_decarboxylase