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
Guanine ring - True are all except ? 
Select and explain. 
A. It has 9 atoms, B. Aspaate acts as the amino group donor for forming guanine, C. Carbonyl group at C6 acts as a hydrogen bond acceptor, D. It forms three hydrogen bonds with cytosine
B: Aspaate acts as the amino group donor for forming guanine
Answer: B: Aspaate acts as the amino group donor for forming guanine 
Explanation: Ans. is 'b' i.e., Asparate acts as the amino group donor for forming guanineGuanine ring is a purine ring. Hence it has nine atoms included in the ring.It is formed from IMP (Inosine Mono Phosphate). IMP undergoes dehydrogenation, in the presence of IMP dehydrogenase (NADP is the coenzyme) to form Xanthosine Mono Phosphate (XMP). XMP undergoes amination with glutamine to form GMP.On the other hand, IMP undergoes amination with Aspaate to form Adenylosuccinate. Adenylosuccinate in the presence of Adenylosuccinate lyase to form AMP and fumarate.