ABSTRACT
DNAs play a central role in molecular biology and genetics, RNAs are used to produce proteins and control gene expression, and proteins produce the characteristics of the cells, including control of gene expression. Members of each category can be extracted, studied, and manipulated to understand more about particular cellular processes or to transform organisms to produce specic products or functions. To purify high-molecular-weight DNA (>50-100 kb) so that it can be used in molecular biology procedures and experiments requires specialized equipment, supplies, and chemicals, but for most samples, it is not especially difcult to extract (Table 19.1). On the other hand, additional chemicals and equipment are needed to purify high-quality RNA, and greater care must be taken to eliminate as much RNase activity as possible. RNAs are generally more reactive than are DNAs, and they are degraded much more readily than are DNAs. During the process of extracting nucleic acids of all types, proteins (including nucleases that degrade DNA and RNA) as well as polysaccharides (some of which can inhibit enzymes used in molecular biology procedures), and other cellular debris are removed. For extraction of RNA, RNase inhibitors are also used.
