REPLICATION AND MAINTENANCE OF THE GENETIC MATERIAL

For normal cell growth and proliferation, the DNA must be protected from various types of damage. Such damage, induced, for example, by uv irradiation, can involve the chemical alteration of the DNA and, consequently, deleterious mutation. Cells are able to correct or repair such damage. One of the best-understood mechanisms of repair involves the synthesis of new DNA, which replaces the damaged portion. This is called repair synthesis of DNA. The extent of repair synthesis is very small in comparison with the DNA synthesis accompanying replication of the chromosomes. 

Most cells (bacteria, plants, and animals) contain one, two, or a small number of most genes. However, in response to certain situations, some cells will produce many copies of a particular gene. This is known as gene or DNA amplification and involves several-fold replication of specific segments of the DNA. 

Faults in DNA replication and repair in animal cells can lead to a predisposition to cancer. This helps to emphasize the importance of these processes in biology. However, much of our understanding of how they occur at the molecular level has depended upon studies with the simpler bacteria. 

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