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<p><b>New page</b></p><div>[[File:Homo_sapiens-mtDNA~NC_012920-ATP8+ATP6_Overlap.svg|thumb|Homo_sapiens-mtDNA~NC_012920-ATP8+ATP6_Overlap.svg]] '''Start codon'''<br />
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A '''start codon''' is a specific sequence of [[nucleotide]]s in [[messenger RNA]] (mRNA) that signals the beginning of [[translation (biology)|translation]]. It is the site at which the [[ribosome]] assembles to begin synthesizing a [[polypeptide]] chain. The most common start codon is [[AUG (start codon)|AUG]], which codes for the amino acid [[methionine]] in [[eukaryote]]s and a modified form of methionine, [[N-formylmethionine]], in [[prokaryote]]s.<br />
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==Function==<br />
The start codon plays a crucial role in the [[genetic code]] by marking the site at which translation into [[protein]]s begins. During the process of translation, the [[ribosome]] identifies the start codon on the mRNA strand and begins to assemble the corresponding amino acids into a polypeptide chain. This process is essential for the accurate synthesis of proteins, which are vital for various cellular functions.<br />
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==Mechanism==<br />
In the initiation phase of translation, the small subunit of the ribosome binds to the mRNA near the 5' end. It then scans along the mRNA until it encounters the start codon. The presence of the start codon ensures that the ribosome assembles at the correct location to begin translation. The start codon is recognized by the initiator [[tRNA]] molecule, which carries the amino acid methionine. This initiator tRNA pairs with the start codon, allowing the large ribosomal subunit to join the complex and begin the elongation phase of translation.<br />
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==Variations==<br />
While AUG is the most common start codon, alternative start codons can be used in certain contexts. In some organisms, other codons such as [[GUG (start codon)|GUG]] and [[UUG (start codon)|UUG]] can also function as start codons, although they are less efficient than AUG. These alternative start codons are typically found in specific genes or under certain conditions.<br />
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==Importance in Genetic Engineering==<br />
The start codon is a critical element in [[genetic engineering]] and [[synthetic biology]]. By manipulating the start codon and the surrounding sequences, scientists can control the expression of genes and the production of proteins. This has applications in various fields, including [[biotechnology]], [[medicine]], and [[agriculture]].<br />
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==Related Concepts==<br />
* [[Stop codon]]<br />
* [[Open reading frame]]<br />
* [[Gene expression]]<br />
* [[Transcription (biology)]]<br />
* [[Translation (biology)]]<br />
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==See Also==<br />
* [[Codon]]<br />
* [[Genetic code]]<br />
* [[Ribosome]]<br />
* [[mRNA]]<br />
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==References==<br />
{{Reflist}}<br />
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==External Links==<br />
{{Commons category|Start codon}}<br />
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[[Category:Genetics]]<br />
[[Category:Molecular biology]]<br />
[[Category:Protein biosynthesis]]<br />
[[Category:Translation (biology)]]<br />
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