生物化学习题之5(英文).doc

Monochoicce 1. The B-DNA structure found in solution is a A. right-handed double helix of antiparallel chains (11 bp/turn). B. left-handed double helix of antiparallel chains (~10 bp/turn). C. right-handed double helix of antiparallel chains (~10 bp/turn). D. left-handed zig-zag helix of antiparallel chains (12 bp/turn). E. right-handed double helix of parallel chains (~10 bp/turn). 2. DNA differs from RNA in the following features A. DNA is resistant to base catalyzed hydrolysis; RNA is hydrolyzed by OH-. B?. DNA residues are linked by 3--5 phosphodiester bonds; RNA is 2--5 linked. C. DNA has deoxyribose residues; RNA has ribose residues. D. DNA contains the A, C, G and T bases; RNA contains A, C, G, and U. E. All but the second choice are correct differences. 3. Because DNA is a highly charged polyanion, its stability to heat denaturation (melting): A. does not depend on hydrophobic interactions. B. increases with increasing [salt]. C. decreases with increasing [salt]. D. is independent of G + C content. E. increases with increasing pH. 4. The total contour length of DNA in a human cell is about A. 1 mm. B. 1 mm. C. 10 cm. D. 1 meter. E. 12 furlongs. 5. Polyacrylamide and agarose gel electrophoresis separate nucleic acids based primarily on their A. length. B. ratio of mass/charge. C. (G+C)/(A+T) content. D. organismal origin. E. content of 15N (buoyant density). 6. The number of supercoils in a covalently-closed, circular DNA can only be changed if A. at least one of the phosphodiester chains is cleaved. B. both of the phosphodiester chains are cleaved. C. histones are bound to the DNA. D. the salt concentration is increased 1.0 M. E. chemical reagents react with the backbone phosphates. 7. Thymidine A. is equal to the adenosine concentration in double-stranded DNA. B. is replaced by Uracil in RNA. C. normally forms 2 hydrogen bonds with adenosine. D. can participate in hydrophobic interactions due to its methyl group. E.? All of the above are correct. 8. The m