1. To study the process of DNA replication, you add the nitrogen isotope N-15 in a culture in which cells are growing. After one cell division, you analyze the DNA and find all the DNA has some N15 in it. You then grow those cells for another generation in a culture with the normal isotope of nitrogen, N-14. This time, you find that half of the DNA has some N-15 in it and half of it has only N-14. From this information, what can you deduce about the process by which DNA replicates?

2. Table below is copied from the textbook.

a. Calculate the ratio of (A+G)/(T+C) for each organism listed in the table.

b. Calculate the ratio of (A+T)/(C+G) for each organism listed in the table.

c. Explain why some the ratios are constant in a, but vary in b. 3. In eukaryotes, DNA is wrapped with proteins, forming a complex called chromatin. There are 5 types of histone proteins in a chromatin: H1, H2A, H2B, H3, and H4. Explain why there are more H2A histone molecules than H1 histone molecules in a chromatin. Do you expect to find more H2A or more H3 histone molecules in a chromatin? Explain your answer. 4. Draw a DNA replication process in a eukaryotic cell. On your drawing, label:

a. Origin

b. Directionality (5′ and 3′ ends) of all template and newly synthesized strands

c. Leading and lagging strands

d. Okazaki fragments

e. RNA primers

5. Define the following proteins’ functions in the DNA replication process:

a. DNA helicase

b. DNA polymerase I

c. DNA polymerase III

d. DNA ligase

e. Primase

f. Topoisomerase

g. Telomerase

h. Single-strand binding proteins