DNA
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DNA is an acronym for deoxyribonucleic acid, a nucleic acid. Nucleic acid is a substance in the nucleus of a cell. The nucleus is part of the cell separated from the rest of the cell by a membrane. DNA can be found in the cells of all organisms. This includes animals, plants, and all other living things. DNA contains the genetic code of the organism. This code is based on the code from that organism's parents. DNA also helps in protein synthesis.
DNA is shaped like a double helix, which is like a ladder twisted into a spiral. Each "leg" of the "ladder" is a line of nucleotides. A nucleotide is a molecule made of ribose (a 5 carbon sugar), a phosphate group, (which is made of phosphorus and oxygen), and a Nitrogen base. Each nucleotide has one of four kinds of bases.
- adenine (A)
- thymine (T)
- cytosine (C)
- guanine (G)
The legs are each made of two bases. The bases connect in the middle. A bases connect only with T bases, and C bases connect only with G bases. The plan for a person, animal, or plant can be found by reading the order of the bases in the DNA.
DNA was first found by F. Miescher in 1869. Miescher did not know what it was, or what it looked like. In the 1950's, Erwin Chargaff discovered that the amount of Thymine (T) present in a molecule of DNA was roughly equal to the amount of Adenine (A) present. He found that the same applies to Guanine (G) and Cytosine (C). A few years after Chargaff's discovery, a British scientist named Rosalind Franklin found that by diffracting X-Rays onto a thin strand of DNA, an "X" pattern was developed. This marked an important step in the discovery of the structure of DNA. In 1953, James Watson and Francis Crick figured out the shape of DNA. Watson and Crick applied Chargaff's, Franklin's, and other scientists' work in creating their model of the DNA double helix.
see also: gene, RNA, chromosome
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