What is a Gene?
Gene, the structural unit of inheritance in living organisms. A gene is, in essence, a segment of DNA that has a particular purpose, i.e., that codes for (contains the chemical information necessary for the creation of) a specific enzyme or other protein. The strands of DNA on which the genes occur are organized into chromosomes. The nucleus of each eukaryotic (nucleated) cell has a complete set of chromosomes and therefore a complete set of genes. Each gene provides a blueprint for the synthesis (via RNA) of enzymes and other proteins and specifies when these substances are to be made. Genes govern both the structure and metabolic functions of the cells, and thus of the entire organism and, when located in reproductive cells, they pass their information to the next generation. Chemically, each gene consists of a specific sequence of DNA building blocks called nucleotides. Each nucleotide is composed of three subunits: a nitrogen-containing compound, a sugar, and phosphoric acid. Geometrically, the gene is a double helix formed by the nucleotides. Gene loci are often interspersed with segments of DNA that do not code for proteins; these segments are termed “junk DNA. When junk DNA occurs within a gene, the coding portions are called exons and the noncoding (junk) portions are called introns. Junk DNA makes up 97% of the DNA in the human genome, and, despite its name, is necessary for the proper functioning of the genes. Each chromosome of each species has a definite number and arrangement of genes. Alteration of the number or arrangement of the genes can result in mutation. When the mutation occurs in the germ cells (egg or sperm), the change can be transmitted to the next generation. Mutations that affect somatic cells can result in certain cancers. The scientific study of inheritance is genetics. The genetic makeup of an organism with reference to its set of genetic traits is called its genotype. The interaction of the environment and the genotype produces the observable attributes of the organism, or its phenotype. The sum total of the genes contained in an organism’s full set of chromosomes is termed the genome. Scientists are working toward identifying the location and function of each gene in the human genome. The decoding of the first free-living organism (a bacterium, Hemophilus influenza) was completed in 1995 by J. Craig Venter and Hamilton Smith.
What is Gene Therapy?
Gene therapy, the use of genes and the techniques of genetic engineering in the treatment of a genetic disorder or chronic disease. There are many techniques of gene therapy, all of them still in experimental stages. The two basic methods are called in vivo and ex vivo gene therapy. The in vivo method inserts genetically altered genes directly into the patient; the ex vivo method removes tissue from the patient, extracts the cells in question, and genetically alters them before returning them to the patient. The challenge of gene therapy lies in development of a means to deliver the genetic material into the nuclei of the appropriate cells, so that it will be reproduced in the normal course of cell division and have a lasting effect. One technique involves removing cells from a patient, fortifying them with healthy copies of the defective gene, and reinjecting them into the patient. Another involves inserting a gene into an inactivated or nonvirulent virus and using the virus’s infective capabilities to carry the desired gene into the patient’s cells. A liposome, a tiny fat-encased pouch that can traverse cell membranes, is also sometimes used to transport a gene into a body cell. Another approach employing liposomes, called chimeraplasty, involves the insertion of manufactured nucleic acid molecules (chimeraplasts) instead of entire genes to correct disease-causing gene mutations. Once inserted, the gene may produce an essential chemical that the patient’s body cannot, remove or render harmless a substance or gene causing disease, or expose certain cells, especially cancerous cells, to attack by conventional drugs. Gene therapy was first used in humans in 1990 to treat a child with adenosine deaminase deficiency (ADA), a rare hereditary immune disorder (see immunity). It is hoped that gene therapy can be used to treat cancer, genetic diseases, and AIDS, but there are concerns that the immune system may attack cells treated by gene therapy, that the viral vectors could mutate and become virulent, or that altered genes might be passed to succeeding generations. In the United States, gene therapy techniques must be approved by the federal government. The Recombinant DNA Advisory Committee of the National Institutes of Health oversees gene therapy experiments. Like drugs, products must pass the requirements of the Food and Drug Administration. Gene therapy is a competitive and potentially lucrative field, and patents have been awarded for certain techniques.
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