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Proteins are made of a chain of 20 different types of [[amino acid]] molecules. This chain folds up into a compact shape, rather like an untidy ball of string. The shape of the protein is determined by the sequence of amino acids along its chain and it is this shape that, in turn, determines what the protein does.<ref name=NIGMS/> For example, some proteins have parts of their surface that perfectly match the shape of another molecule, allowing the protein to bind to this molecule very tightly. Other proteins are [[enzyme]]s, which are like tiny machines that alter other molecules.<ref>[http://www.howstuffworks.com/cell2.htm Enzymes] HowStuffWorks, Accessed 20 May 2008</ref>
The information in DNA is held in the sequence of the repeating units along the DNA chain.<ref name=nih>[http://ghr.nlm.nih.gov/handbook/basics/dna What is DNA?] Genetics Home Reference, Accessed 16 May 2008</ref> These units are four types of [[nucleotide]]s (A, T, G and C) and the sequence of nucleotides stores information in an alphabet called the [[genetic code]]. When a gene is read by a cell the DNA sequence is copied into a very similar molecule called [[RNA]] (this process is called [[Transcription (genetics)|transcription]]). Transcription is controlled by other DNA sequences (such as [[Promoter (biology)|promoters]]), which show a cell where genes are, and control how often they are copied. The RNA copy made from a gene is then fed through a structure called a [[ribosome]], which translates the sequence of nucleotides in the RNA into the correct sequence of amino acids and joins these amino acids together to make a complete protein chain. The new protein then folds up into its active form. The process of moving information from the language of RNA into the language of amino acids is called [[protein biosynthesis|translation]].<ref name=nobel>[http://nobelprize.org/educational_games/medicine/dna/index.html DNA-RNA-Protein] Nobelprize.org, Accessed 20 May 2008</ref>
[[File:DNA replication split.svg|thumb|left|[[DNA replication]]. DNA is unwound and [[nucleotide]]s are matched to make two new strands.]]
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