Question

1. Describe one experiment that can test the hypothesis that DNA replication is semi conservative. Describe the results of this experiment if replication was conservative. And if it was distributive?

2. What type of chemical bond contributes to the specificity of base paring in the DNA? Are there any other chemical or physical factors in the structure o f the DNA molecule contributing to the thermodynamic stability of the DNA?

3. List the m ajor differences between DNA and RNA.

4. Explain how DNA binding protein s recognize specific sequences in the DNA at the molecular level .

5. What property of RNA makes possible for RNA molecules to function as enzymes?

6. Explain the concept of topoisomers wh en referring to DNA molecules .

7. Explain the meaning of the linking Number.

8. Explain the difference in enzymatic activity between DNA Topoisomerase I and II.

9. Can you test the activity of topoisomerases doing in vitro assays? How?

10. Discuss the nature and origin of pseudogenes.

11. Describe the three major classes of DNA sequence components in eukaryote genomes .

12. Does genome size directly correlate with the organism ’s complexity? Reason your answer .

13. Explain why each chromosome in a eukaryotic ce ll contains multiple origins of replication , but includes only one centromere.

14. Explain the role of monovalent and bivalent attachment of microtubules to centromeres in mitosis and meiosis.

15. describe the different phases of cell cycle, and the function of GAPs during cell cycle.

16. Explain the roles of Cohesin and C ondensin in cell division.

17. Explain the difference between homologous chromosomes and sister chromatids .

Answer 1

1. To show that DNA replication is semi conservative in nature, we will use E coli. This classic experiment was given by Meselson and Stahl.

A. Grow E coli cells on a medium containing N14 (light nitrogen) for many generations. E coli DNA will incorporate N14 into it.

B. Now, grow these cells on N15 (heavy nitrogen) for two successive generations.

You will see the following results.

Presence of hybrid DNA after first generation and hybrid DNA and heavy DNA after second generation, confirms that DNA replication is semi conservative in nature. As per this model, in newly synthesized daughter DNA molecule, one of the strands is of parental origin and the other strand is newly synthesized.

If it would have been conservative, you will see only heavy and light DNA strands in both the generations. No hybrid DNA would be seen.

It it would have been dispersive, you will see only hybrid DNA in both the generations. Neither light nor heavy DNA would be seen.

See figures below -

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