3 generation of sequencing of dna sequence homologous rna instead of dna
Answers
Until the early 1970s DNA was the most difficult cellular molecule for the biochemist to analyze. Enormously long and chemically monotonous, the string of nucleotides that forms the genetic material of an organism could be examined only indirectly, by protein or RNA sequencing or by genetic analysis. Today the situation has changed entirely. From being the most difficult macromolecule of the cell to analyze, DNA has become the easiest. It is now possible to isolate a specific region of a genome, to produce a virtually unlimited number of copies of it, and to determine the sequence of its nucleotides overnight. At the height of the Human Genome Project, large facilities with automated machines were generating DNA sequences at the rate of 1000 nucleotides per second, around the clock. By related techniques, an isolated gene can be altered (engineered) at will and transferred back into the germ line of an animal or plant, so as to become a functional and heritable part of the organism's genome.
These technical breakthroughs in genetic engineering—the ability to manipulate DNA with precision in a test tube or an organism—have had a dramatic impact on all aspects of cell biology by facilitating the study of cells and their macromolecules in previously unimagined ways. They have led to the discovery of whole new classes of genes and proteins, while revealing that many proteins have been much more highly conserved in evolution than had been suspected. They have provided new tools for determining the functions of proteins and of individual domains within proteins, revealing a host of unexpected relationships between them. By making available large amounts of any protein, they have shown the way to efficient mass production of protein hormones and vaccines. Finally, by allowing the regulatory regions of genes to be dissected, they provide biologists with an important tool for unraveling the complex regulatory networks by which eucaryotic gene expression is controlled.
Recombinant DNA technology comprises a mixture of techniques, some new and some borrowed from other fields such as microbial genetics (Table 8-7). Central to the technology are the following key techniques: