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
1" carbon of pentose sugar of nucleic acid joins - 
Select and explain. 
A. N-9 of pyrimidine, B. N-1 of pyrimidine, C. N-1 of purine, D. None of the above
B: N-1 of pyrimidine
Answer: B: N-1 of pyrimidine 
Explanation: Ans. is 'b' i.e., N-1 of pyrimidinePenose sugars Pentose sugar present in DNAs is deoxyribose and in RNAs it is ribose. A pentose sugar (ribose or deoxyribose) is linked to a nitrogenous base (purine or pyrimidine) covalent N-glycosidic bond to form nucleoside.This linkage joins the Carbon-1 ofpentose sugar with nitrogen-9 of the purine base or nitrogen-I of pyrimidine base.Nucleoside is linked to phosphoric acid to form nucleotide.For example, purine base 'adenine' combines with ribose sugar to form adenosine, a nucleoside (ribonucleoside). o This, adenosine (nucleoside) combines with phosphate group to form adenosine monophosphate : AMP, a nucleotide (ribonucleotide).If the pentose sugar is deoxyribose (instead of ribose) the resulting nucleotide is deoxyribonucleotide.Adenine + Ribose Adenosine (ribonucleoside 4 AMP (ribonucleotide)Phosphate groupAdenine + Deoxyribose Deoxyadenosine (Deoxynucleoside) 4 dAMP (deoxyribonucleotide) Phosphate group