1. Can you think of any other mechanisms besides topoisomerase activity that could release supercoiling in replicating DNA? 2. In developing sea urchins, just after fertilization, the cells divide...

1. Can you think of any other mechanisms besides topoisomerase activity that could release supercoiling in replicating DNA?

2. In developing sea urchins, just after fertilization, the cells divide every 30–40 min. In the adult, the cells divide once every10–15 h. The amount of DNA per cell is the same in each case, but the DNA obviously replicates much faster in developing cells. Propose an explanation to account for the difference in replication time

3. Mutants are used to study various aspects of the phenotype and genotype. How can we study genes that are critically important in the functioning of an organism? For example, how do we study mutations in the gene for DNA polymerase III in E. coli, when changes in this gene are usually lethal? Remember, to study the genes in bacteria, we need the bacteria to grow and form colonies in order to be scored for their phenotypes.