DNA
From Simple English Wikipedia, the free encyclopedia
'DNA' short for deoxyribonucleic acid', 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. 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 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 defracting X-Rays onto a thin strand of DNA, an "X" pattern was developed. This marked an important step in the discovery of the form 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.
[edit] DNA reproduction
DNA reproduces itself by splitting in half and then reforming the missing side. First, the DNA molecule is split down the middle by a molecule called DNA helicase. After the DNA molecule is in two separate pieces, another molecule called DNA polymerase which 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 itself.
[edit] Protein synthesis
Proteins are created in ribosomes inside a cell. However, the protein needs a special code called a codon to create a protien. 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 protiens are made.
