Deoxyribonucleic acid (DNA) is an organic substance occurring in chromosomes contained in the nuclei of cells, which encodes and carries genetic information and is the fundamental element of heredity.
As the transmitter of inherited characteristics, deoxyribonucleic acid (DNA) replicates itself exactly and determines the structure of new organisms. It does this by governing the structure of their proteins.
The Swiss researcher Friedrich Miescher (1844– 1895) first discovered DNA in 1869 when he extracted a substance which he called nuclein, containing nitrogen and phosphorus, from cell nuclei. Until the molecular structure of DNA was determined in 1953 by the work of American biochemist James D. Watson (1928–), British biochemist Francis Crick (1916–2004), and Maurice Wilkins (1916–2004), a British biophysicist, it was not possible to ascertain whether nucleic acids, proteins, or both carried the information that makes the genes of every organism unique. The thousands of genes that make up each chromosome are composed of DNA, which consists of the five-carbon sugar deoxyribose, phosphate, and four types of nitrogen-containing molecules (adenine, guanine, cytosine, and thymine). The sugar and phosphate combine to form the outer edges of a double helix. The nitrogen-containing molecules appear in bonded pairs, similar to the rungs of a ladder, connecting the outer edges. They are matched in an arrangement that always pairs adenine in one chain with thymine in the other, and guanine in one chain with cytosine in the other. A single DNA molecule may contain several thousand pairs.
Many viruses are also composed of DNA, which may have a single-strand form rather than a double helix. Each particle of a virus contains only one DNA molecule, ranging in length from 5,000 to over 200,000 subunits. Radiation, thermal variations, chronic substance use, or the presence of certain potentially toxic chemicals can cause changes to an organism's DNA pattern, resulting in genetic mutation that may be heritable (passed on to offspring). Over the course of evolution, such mutations provided the hereditary blueprints for the emergence of new species.
Since the 1970s, scientists have advanced their understanding of the molecular structure of genes through experiments with recombinant DNA. As its name suggests, this technique combines fragments of DNA from different source materials, allowing for the creation of new biological combinations not found in nature. Recombinant DNA can be from two different species of organism or may be entirely synthesized in a laboratory.
See also Darwin, Charles Robert; Genetic counseling; Heredity ; Ribonucleic acid (RNA) .
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