Application Questions And Problems

Compare and contrast prokaryotic and eukaryotic chromosomes. How are they alike and how do they differ?

(a) In a typical eukaryotic cell, would you expect to find more molecules of the H1 histone or more molecules of the H2A histone? Explain your reasoning. (b) Would you expect to find more molecules of H2A or more molecules of H3? Explain your reasoning.

22. Suppose you examined polytene chromosomes from the salivary glands of fruit fly larvae and counted the number of chromosomal puffs observed in different regions of DNA.

(a) Would you expect to observe more puffs from euchromatin or from heterochromatin? Explain your answer.

(b) Would you expect to observe more puffs in unique- sequence DNA, moderately repetitive DNA, or repetitive DNA? Why?

*23. A diploid human cell contains approximately 6 billion base pairs of DNA.

(a) How many nucleosomes are present in such a cell? (Assume that the linker DNA encompasses 40 bp.)

(b) How many histone proteins are complexed to this DNA?

*24. Would you expect to see more or less acetylation in regions of DNA that are sensitive to digestion by DNase I? Why?

25. A YAC that contains only highly repetitive, nonessential DNA is added to mouse cells that are growing culture. The cells are then divided into two groups, A and B. A laser is then used to damage the centromere on the YACs in cells of group A. The centromeres on the YACs of group B are not damaged. In spite of the fact that the YACs contain no essential DNA, the cells in group A divide more slowly than those in group B. Provide a possible explanation.

26. Species A possesses only unique-sequence DNA. Species B possesses unique-sequence DNA and highly repetitive DNA. Species C possesses only moderately repetitive DNA. The genomes of all three species are similar in size. A student performs typical renaturation reactions with DNA from each species and plots a C0t curve for each. Draw a C0t curve for the renaturation reaction of each species.

*27. Which of the following two molecules of DNA has the lower melting temperature? Why?

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