Answer to Question #307258 in Genetics for boo

Question

The regulation of replication is essential to genomic stability, and, normally, the DNA is replicated just

once every eukaryotic cell cycle (in the S phase). Normal cells produce protein A, which increases in

concentration in the S phase. In cells that have a mutated copy of the gene for protein A, the protein is

not functional and replication takes place continuously throughout the cell cycle, with the result that

cells may have 50 times the normal amount of DNA. Protein B is normally present in G1 but disappears

from the cell nucleus in the S phase. In cells with a mutated copy of the gene for protein A, the levels of

protein B fail to disappear in the S phase and, instead, remain high throughout the cell cycle. When the

gene for protein B is mutated, no replication takes place.

Propose a mechanism for how protein A and protein B might normally regulate replication so that each

cell gets the proper amount of DNA. Explain how mutation of these genes produces the effects just

described.

Answer 1

DNA replication is semiconservative. Each strand in the double helix acts as a template for synthesis of a new, complementary strand. New DNA is made by enzymes called DNA polymerases, which require a template and a primer (starter) and synthesize DNA in the 5' to 3' direction.