Genetic Engineering. Every cell contains the full set of genetic information (genome) needed to reconstruct the entire organism. The information (gene) for making each cell product is encoded as a specific sequence of nucleic acids in a specific part of a long DNA molecule. The DNA is used as a template for the production (transcription) of a messenger-RNA molecule, which carries the message from the nucleus, where the DNA molecules are located, to the protein-building apparatus (ribosomes) where the specified proteins are made (translation).
It is now possible to genetically engineer new transgenic organisms by moving the genes coding for useful characteristics from one organism to another. Typically, the original DNA molecules are first cut into fragments by special enzymes (restriction endonucleases). Next the desired fragments are inserted into bacteria. As the bacteria grow, the new DNA-message is copied (cloned) and amplified many times. These genes can then be "harvested" and spliced into vectors, organisms that can transfer the gene to the target animal or plant. If appropriate reading instructions (control sequences) are also transferred, the gene can function normally, ordering the production (expression) of its proteins in its new (transgenic) host. Such precise gene transfer differs markedly from classical sexual breeding where the genes of both parents can be shuffled pretty much at random.
Plant Tissue Culture. Various auxiliary biotechnologies can facilitate and expand the usefulness of such manipulations. For example, plant cells can be grown by the millions in plant tissue culture (PTC), where they can be easily studied, manipulated and selected for superior traits -- without waiting a full season for the plants to grow. Often the rigid cellulose cell walls are first removed, leaving bare protoplasts. Using special chemical messengers (hormones), each cell can then be regenerated into a full plant and grown normally in the field.
Monoclonal Antibodies. Other important biotechnologies involve immunological techniques. The entrance of a recognizably foreign substance (antigen) into the body triggers a defensive immune response, in which special white blood cells (lymphocytes) produce antibody proteins to neutralize the intruder. If a cell producing a specific desired antibody can be located, it can be fused with a rapidly growing cancer cell to produce hybrid cells that churn out large quantities of that specific (monoclonal) antibody. Since antibodies lock onto their corresponding antigens, as a lock fits a corresponding key, these monoclonal antibodies make excellent probes to detect the presence of their antigens. ELISA (enzyme-linked immunosorbant assay) diagnostic tests are particularly sensitive. First special organic catalysts (enzymes) are attached to the antibodies. Antibodies not locking onto their antigens are flushed away, and then appropriate reactants are added. The remaining antigen-immobilized enzyme (if present) catalyzes the reaction, producing large amounts of detectable products to signal the antigen's presence.