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Problem Set 5 ANSWER KEY 2010

Problem Set 5 ANSWER KEY 2010 - Problem Set 5 Chapters 16...

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Problem Set 5 BILD1 / Winter 2010 Chapters 16 - 18 Traver 1 DNA 1) How did the use of the following radioisotopes – 35 S, 32 P and 15 N – help demonstrate that the genetic material was DNA, and that the Watson and Crick model of DNA was correct? 35 S and 32 P were used to selectively label either proteins ( 35 S incorporation into amino acids) or DNA ( 32 P incorporation into nucleic acids) of the virus, T2. Bacteria infected with 35 S- or 32 P-labeled T2 were purified (pelleted) from the viral-containing medium. Only infected 32 P-labelled bacteria were recovered, indicating that only 32 P-labelled DNA functioned as T2 genetic material. (Note: 35 S-labelled T2 could also infect bacteria, but the labeled proteins were not transmitted in the infection) 15 N was used to pulse-label bacterial DNA to test different models of replication. 15 N-labelled bacteria were then grown in lighter isotope, 14 N, which would selectively label newly replicated DNA. Bacterial DNA was separated by isotopic weight following each round of replication. The pattern of DNA density indicated that DNA replication occurred by semiconservative mechanism. 2) (a) Draw in schematic form the nucleotide dCTP. Point out the 5’ end and the 3’ end. (b) Draw out the reaction for the addition of a second base to this nucleotide. (c) What was the energy source for this reaction? Hydrolysis of pyrophosphate (P-Pi) into two inorganic phosphates, released from added nucleoside triphosphate. (d) How does dCTP differ from CTP? dCTP contains deoxyribose sugar (H group at 2’ Carbon) CTP contains ribose sugar (OH group at 2’ Carbon) 3) What is Chargaff’s rule and how did the Watson-Crick structure of DNA explain this rule? Each species contain an equivalent number of A (adenine) and T (thymine) bases, and an equivalent number of G (guanine) and C (cytosine) bases. Chargaff’s rules helped Watson and Crick determine the specific combination of base pairing that always occurs in double stranded DNA (A + T, G + C) 4) You have a DNA strand with the following linear sequence of bases: 5’ – G G C C C A T G A C C T C T A G – 3’ 3’ – C C G G G T A C T G G A G A T C – 5’ (a) What is the sequence of the complementary strand? Above, draw an arrow in the direction that replication would occur for polymerization of the complementary strand.
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