MUTATIONS AND CELL DEFENSES

INTRODUCTION
The information required for the development and growth of an organism is encoded in its deoxyribonucleic acid (DNA), the genetic material. In human cells, the entire DNA content, or genome, is packaged in 46 chromosomes that reside in the cell’s nucleus. Because this information is critically important for all biological processes occurring during the lifetime of an organism, evolution has resulted in many and various means by which a cell can either avoid damage to this information, or repair damage once it has occurred.

DNA is a double-strandedhelical ribbon, with each strand consisting of a continuous sequence of bases. Bases can be considered as the letters of words that are strung together to make up the information code. Remarkably, only four bases—adenine, guanine, cytosine, and thymine (A, G, C, and T)—are required to generate the amazingly diverse information encoded in the human genome, and it is the varying, ordered sequence of these bases that creates all the different bits of information along the DNA strand. For the purposes of our discussion in this chapter, remember that genetic information is decoded by the following general path: DNA codes for ribonucleic (RNA), acid which in turn codes for protein molecules, whose amino acid sequence derives from the DNA sequence. Although this is an oversimplification of the complex information contained within DNA, it suffices for our appreciation of how changes in the DNA sequence (mutations) may adversely effect cellular function.