Name: Practice EXAM 2-cell Biology Spring 2017 MULTIPLE CHOICE. 15 Questions. Ch

Question

Name: Practice EXAM 2-cell Biology Spring 2017 MULTIPLE CHOICE. 15 Questions. Choose the one alternative that best completes the statement or answers the question. 1) The famous Meselson-Stahl experiments that demonstrated the semi-conservative model of DNA replication did so utilizing: a) E. coli mutants deficient in DNA replication b) DNA purification by gel electrophoresis c) Density gradient centrifugation of isotope-labeled DNA d) Calf thymus DNA e) b) and d) above 2) was a component of Kornberg's biochemical assay for DNA polymerase activity that he was not aware of, but nevertheless allowed the experiment to work. This component was: provide a template for DNA a) Contamination of E. coli DNA in the cell extracts to b) replication during purification The template DNA he used was damaged (nicked and gapped) c) activity of DNA helicase in the assay, which separated the template DNA into single parental strands for copying by DNA polymerase d) activity of DNA Primase in the assay, which provided 3-oH groups for e) Presence of mutants of E. coli that did not require DNA polymerase I Daughter Parental strands strands 3) considering the direction of the replication fork in the figure above,how would the daughter DNA strand with the marked 5' end be replicated? a) Continuously, it is the leading strand b) Discontinuously, it is the lagging strand c) Continuously or discontinuously, both are equally possible d) impossible to determine with the information given Cell Bio Practice Exam 2, Page 1

Explanation / Answer

Following are the answers to the given multiple choice questions:

1) c. Density gradient centrifugation of isotope labelled DNA.

In this experiment, N-15 was used and the labeled daughter DNA were characterized by density gradient centrifugation.

2) b) The template DNA he used was damaged (nicked and gapped) during purification

3) b) Discontinuously, it is the lagging strand

4) b) False

5) d) It is more heat-stabile than other DNA polymerases

6) d) DNA Ligase

7) a) Continuously, it is the leading strand

8) d) Helicase

9) a) proof that the two DNA Polymerase III enzymes situated at the replication fork are facing opposite directions at the replication fork

10) c) 6

11) d) 5' TACGCGTA 3'

12) a) DNA polymerization occurs in 5' to 3' direction.

13) c)Drosophila chromosomes might contain many more number of origins of replication than E. coli chromosome.

14) c) 24%

15) d) Topoisomerases

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