Editing N-terminus (section)

==Chemistry==
Each amino acid has an [[amine]] group and a [[carboxylic group]]. Amino acids link to one another by [[peptide bond]]s which form through a [[dehydration reaction]] that joins the carboxyl group of one amino acid to the [[amine]] group of the next in a head-to-tail manner to form a [[Peptide|polypeptide]] chain. The chain has two ends – an amine group, the N-terminus, and an unbound carboxyl group, the [[C-terminus]].<ref name="Voet, Voet, Pratt">{{cite book|last1=Voet|first1=Donald|last2=Voet|first2=Judith G.|last3=Pratt|first3=Charlotte W.|title=Fundamentals of Biochemistry: Life at the Molecular Level|date=2013|publisher=Wiley|location=Hoboken, NJ|isbn=978-0470547847|edition=4th}}</ref>

When a protein is [[translation (biology)|translated]] from [[messenger RNA]], it is created from N-terminus to C-terminus. The amino end of an amino acid (on a charged [[transfer RNA|tRNA]]) during the elongation stage of translation, attaches to the carboxyl end of the growing chain. Since the [[start codon]] of the [[genetic code]] codes for the amino acid [[methionine]], most protein sequences start with a [[methionine]] (or, in bacteria, [[mitochondria]] and [[chloroplast]]s, the modified version [[N-Formylmethionine|''N''-formylmethionine]], fMet). However, some proteins are modified [[posttranslational modification|posttranslationally]], for example, by cleavage from a [[protein precursor]], and therefore may have different amino acids at their N-terminus.