Chem 471 Exam 2 Material (ALL SOLVED)

Nucleoside vs. tide correct answers nucleoside: no phosphate group tide: A vs. B form of helix correct answers (both right handed) B: -predominant form in aq. -B can accommodate a spine of water molecules lying in the minor groove (not A): H bonding between h2o and DNA contributes to stability of B form -slightly tilted A: -RNA = always A b/c of steric hindrance in B w/ extra hydroxyl group -grooves are nearly equal -Bases lie farther to the outside and are strongly tilted with respect to the helix axis X-ray diffraction correct answers shows how things are spaced in area cross shaped pattern = helical structure --Spacing b/w lines = inversely proportion to repeat/c, which (in this case) = pitch -Cross patterns repeat every 4 lines -Tells us there are exactly 4 residues per turn in the helix -Rise = c/4 Crystallography correct answers get distances and can calculate positions/electron density distribution -use metal atom=isomorphous replacement to see differences (3 or 7 from +2) Crystallography advantages/disadvantages correct answers -greatest source for detailed structural info -can be used for any molecule that yields diffraction quality crystals (limitation) Crystallography vs other things correct answers in solution: The greatest advantages of these techniques vs. crystallography are (1) access to more dynamic states in solution (2) most of these techniques are not destructive. Gene cloning developments correct answers 1: characterization of plasmids = small, circular DNA molecules capable of independent replication w/in bacterial cells