History of Molecular Genetics and Biotechnology Help
History of Molecular Genetics and Biotechnology
Prior to discovery that the chemical nature of the gene was DNA, in the early 1900s the gene was an abstract unit of heredity. This period in history is referred to as classical or formal genetics. Classical genetics was extremely successful in elucidatingmany basic biological principles without understanding the physical nature of the gene. The era of molecular genetics began with the discovery of DNA structure in 1953. In the late 1970s, yet another milestone in genetics was reached when researchers found that they could manipulate DNA molecules in a test tube (in vitro), essentially "cloning" the first gene. This discovery led to further molecular genetic advances including recombinant DNA technology (genetic engineering) and spawned the biotechnology industry known today.
The histories of most scientific disciplines are generally characterized by relatively long periods of stagnation punctuated by bursts of rapid progress. Most of these flurries of research are initiated by new technical developments. This is certainly true of biochemistry and molecular biology. At least three major areas of technology have been influential in this respect: (1) instrumentation and techniques, (2) radioactive and fluorescent labels, and (3) nucleic acid enzymology. Beyond these technological influences, the use of computer technology to process biological information (i.e., DNA nucleotide sequences or protein amino acid sequences) is driving new discoveries in molecular genetics and biotechnology. In fact, several new fields within molecular genetics—Bioinformatics, Genomics, and Proteomics—have been created. Each of these fields integrates the use of computer hardware and software to store, process and analyze biological information, such as DNA or protein sequences.
The Analytical Ultracentrifuge
The analytical ultracentrifuge was developed in the 1920s by Theodor Svedberg. The sedimentation rate of a substance during ultracentrifugation is mainly a function of its density and secondarily of its shape. The unit of sedimentation (S, in honor of Svedberg) is an expression of these parameters. The centrifuge has been modified for isolating organelles such as nuclei, ribosomes, mitochondria, and chloroplasts. It can be used for determining the minimum number of kinds of macromolecules in a biological specimen and for estimating the molecular weights of macromolecules.
The Electron Microscope
The electron microscope was invented in the 1930s, and eventually enabled the direct visualization not only of cellular substructures but also of viruses and macromolecules. Circular genetic maps of microorganisms have been shown by electron microscopy to have a corresponding circular physical structure. Multiple ribosomes attached to an mRNA molecule (polysomes) have also been visualized by this instrument.
Electrophoresis is a technique that separates molecules according to their shapes, net charges, and molecular weights in an electric field, usually on solid or semisolid support media such as paper or agarose. This technique was first used in 1949 to differentiate sickle-cell hemoglobin from normal hemoglobin. Protein sequence analysis later revealed that the difference in electrophoretic mobilities of proteins was due to a single amino acid change in the β-chains. Electrophoresis is now used in a variety of DNA and protein analysis applications. Agarose gels are usually employed to isolate and estimate the size of DNA fragments, and DNA sequencing results are obtained using similar gel matrices. Proteins are often analyzed for their size and charge using polyacrylamide gels. Electrophoresis has been extensively used to differentiate isozymes, i.e., proteins possessing the same enzymatic properties but differing in primary structure. Techniques have also been developed for two-dimensional gel electrophoresis (2-D) to further separate mixtures of proteins that might be of similar sizes (or mass) but have slightly different charges (or isoelectric points). These types of gels are first run in one dimensions using size as the separator then, using pH (an indicator of charge), proteins are separated from one another at a 90 degree angle to the size dimension. Complex images of protein "spots" are created using this technique. Researchers can physically isolate the protein from the gel matrix and subject it to mass spectrometry to determine the sequence of some of the amino acids within the spot.
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