DNA
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DNA, short for deoxyribonucleic acid, is a nucleic acid. Nucleic acid is a substance in the middle of a cell. The nucleus is part of the cell separated from the rest of the cell by a wall. DNA can be found in the cells of all living things, also known as organisms. This includes animals, plants, and all other living things, like germs. DNA contains the genetic code of the organism. This code is based on the code from that organism's parents. DNA also helps in making protein.
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[change] DNA structure
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 deoxyribonucleic (a kind of 5 carbon sugar), a phosphate group, (which is made of phosphorus and oxygen), and a nitrogen base. DNA has four nitrogen bases:
The "rungs" of the DNA ladder 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. Between these bases is a covalent bond. The reason that "A" can only connect with "T" is that the bonds have to match up. Adenine and thymine have two hydrogen bonds and cytosine and guanine have three hydrogen bonds. Even though they look the same size the bonds wouldn't match up! The code or plan for a person, animal, or plant can be found by reading the order of the nitrogen bases in the DNA. like mutations.
[change] Copying DNA
DNA is copied in a process called DNA replication. To do this, the two strands of the DNA are split in half and then the missing side is reformed. First, an enzyme called DNA helicase splits the DNA down the middle. After the DNA molecule is in two separate pieces, another molecule called DNA polymerase synthesizes, or makes, the corresponding side of the DNA molecule. Because DNA's nitrogenous bases can only pair in one way, the replicated DNA makes an exact opposite corresponding side to elswhere in space.
[change] Protein synthesis
Proteins are created in ribosomes inside a cell. However, the protein needs a special code called a codon to create a protein. The codon can be found in DNA, but DNA never leaves the nucleus. Because DNA can't leave the nucleus, the DNA copies itself again, but in a different form. This one-stranded copy of DNA is called RNA. There are three types of RNA: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). The messenger RNA is synthesized in a process called transcription. The DNA unwinds with a DNA helicase and splits apart, and an RNA polymerase synthesizes the appropriate bases for RNA. The mRNA, once completed, leaves the cell and goes to the ribosome, where proteins are made.
[change] History
DNA was first isolated by Swiss physician Friedrich Miescher in 1869, who discovered a microscopic substance in the pus of discarded sugical bandages. As it was in the nuclei of cells, he called it "nuclein".[1] In 1919 this discovery was followed by Phoebus Levene's identification of the base, sugar and phosphate nucleotide unit.[2] In the 1950's, Erwin Chargaff found 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. James and Francis never found out what the shape was. They simply stole the notes from Franklin. In 1953, James Watson and Francis Crick figured out the shape of DNA from Rosiland's stolen notes. They took all the credit with another scientist. It was Rosiland's helper that let James and Francis see the notes. Apparently she didnt like Rosiland very much.[needs proving]
[change] See also
[change] References
- ↑ Dahm R (2005). "Friedrich Miescher and the discovery of DNA". Dev Biol 278 (2): 274–88.
- ↑ Levene P, (1919). "The structure of yeast nucleic acid". J Biol Chem 40 (2): 415–24.
