91Ó°ÊÓ

In acidic solutions, nucleosides are hydrolyzed to a sugar and a heterocyclic base. Propose a mechanism for this reaction.

RNAase, the enzyme that catalyzes the hydrolysis of RNA, has two catalytically active histidine residues at its active site. One of the histidine residues is catalytically active in its acidic form, and the other is catalytically active in its basic form. Propose a mechanism for RNAase.

Indicate whether each functional group of the five heterocyclic bases in nucleic acids is a hydrogen bond acceptor (A), a hydrogen bond donor (D), or both (D/A).