BIO 401/501 ADVANCED BIOLOGICAL CHEMISTRY

Nucleic Acids: Homework I

1. The substituted furanose ring found in DNA and RNA displays preferred puckering modes, whereas an unsubstituted ring freely adopts any puckering mode. a) Draw and name the two major puckered modes found in polynucleotides. b) Explain why these two modes (and their relatives) are preferred (2 sentences).

2. In double helical nucleic acids, the bases are sequestered inside the helix the sugar-phosphate backbones are exposed to solvent. Speculate as to what the forces which drive the formation of this folded structure and what physical and/or structural characteristic(s) of each of the subunits of the nucleotide (base, sugar, phosphate) contribute to the stability of this folded structure (4 sentences).

3. In a free nucleotide monomers (and in some polynucleotides), the gross value of c and the sugar pucker are correlated. a) Name and distinguish between the two classes of c angles. Be sure to use a definition of c which is useful for both purines and pyrimidines (2 sentences). b) Explain the structural origin of the correlation of c and pucker (2-3 sentences).