N - terminus - wikipedia N - terminus `` N - term '' redirects here. For the divergence test, see Term test. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( January 2017 ) A tetrapeptide ( example : Val - Gly - Ser - Ala ) with green highlighted N - terminal α - amino acid ( example : L - valine ) and blue marked C - terminal α - amino acid ( example : L - alanine ). This tetrapeptide could be encoded by the mRNA sequence 5 ' - GUU GGU AGU GCU - 3 '. The N - terminus ( also known as the amino - terminus, NH - terminus, N - terminal end or amine - terminus ) is the start of a protein or polypeptide referring to the free amine group ( - NH ) located at the end of a polypeptide. Normally the amine group is bonded to another carboxylic group in a protein to make it a chain, but since the end of a protein has only 1 out of 2 areas chained, the free amine group is referred to the N - terminus. By convention, peptide sequences are written N - terminus to C - terminus, left to right in LTR languages. This correlates the translation direction to the text direction ( because when a protein is translated from messenger RNA, it is created from N - terminus to C - terminus - amino acids are added to the carbonyl end ). Contents 1 Chemistry 2 Function 2.1 N - terminal targeting signals 2.1. 1 Signal peptide 2.1. 2 Mitochondrial targeting peptide 2.1. 3 Chloroplast targeting peptide 3 N - terminal modifications 3.1 N - Myristoylation 3.2 N - Acylation 4 See also 5 References Chemistry Each amino acid has an amine group and a carboxylic group. Amino acids link to one another by peptide bonds 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 polypeptide chain. The chain has two ends - an amine group, the N - terminus, and an unbound carboxyl group, the C - terminus. When a protein is translated from messenger RNA, it is created from N - terminus to C - terminus. The amino end of an amino acid ( on a charged 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 chloroplasts, the modified version N - formylmethionine, fMet ). However, some proteins are modified posttranslationally, for example, by cleavage from a protein precursor, and therefore may have different amino acids at their N - terminus. Function N - terminal targeting signals The N - terminus is the first part of the protein that exits the ribosome during protein biosynthesis. It often contains signal peptide sequences, `` intracellular postal codes '' that direct delivery of the protein to the proper organelle. The signal peptide is typically removed at the destination by a signal peptidase. The N - terminal amino acid of a protein is an important determinant of its half - life ( likelihood of being degraded ). This is called the N - end rule. Signal peptide Main article : Signal peptide The N - terminal signal peptide is recognized by the signal recognition particle ( SRP ) and results in the targeting of the protein to the secretory pathway. In eukaryotic cells, these proteins are synthesized at the rough endoplasmic reticulum. In prokaryotic cells, the proteins are exported across the cell membrane. In chloroplasts, signal peptides target proteins to the thylakoids. Mitochondrial targeting peptide The N - terminal mitochondrial targeting peptide ( mtTP ) allows for the protein to be imported into the mitochondrion. Chloroplast targeting peptide The N - terminal chloroplast targeting peptide ( cpTP ) allows for the protein to be imported into the chloroplast. N - terminal modifications Protein N - termini can be modified co - or posttranslationally. Modifications include the removal of initiator methionine ( iMet ) by aminopeptidases, attachment of small chemical groups such as acetyl, propionyl and methyl, and the addition of membrane anchors, such as palmitoyl and myristoyl groups N - terminal acetylation Main article : N - terminal acetylation N - terminal acetylation is a form of protein modification that can occur in both prokaryotes and eukaryotes. It has been suggested that N - terminal acetylation can prevent a protein from following a secretory pathway. N - myristoylation Main article : Myristoylation The N - terminus can be modified by the addition of a myristoyl anchor. Proteins that are modified this way contain a consensus motif at their N - terminus as a modification signal. N - acylation Main article : Palmitoylation The N - terminus can also be modified by the addition of a fatty acid anchor to form N - acylated proteins. The most common form of such modification is the addition of a palmitoyl group. See also TopFIND, a scientific database covering proteases, their cleavage site specificity, substrates, inhibitors and protein termini originating from their activity References Jump up ^ Reusch, William ( 5 May 2013 ). `` Peptides & Proteins ''. Michigan State University Department of Chemistry. Jump up ^ Voet, Donald ; Voet, Judith G. ; Pratt, Charlotte W. ( 2013 ). Fundamentals of Biochemistry : Life at the Molecular Level ( 4th ed. ). Hoboken, NJ : Wiley. ISBN 0470547847. Jump up ^ Varland ( April 21, 2015 ). `` N - terminal modifications of cellular proteins : The enzymes involved, their substrate specificities and biological effects ''. Proteomics. 15 : 2385 -- 401. doi : 10.1002 / pmic. 201400619. PMC 4692089. PMID 25914051. Jump up ^ Arnesen, Thomas ( May 31, 2011 ). `` Towards a Functional Understanding of Protein N - Terminal Acetylation ''. PLoS Biology. 9 : e1001074. doi : 10.1371 / journal. pbio. 1001074. PMC 3104970. PMID 21655309. Retrieved from `` https://en.wikipedia.org/w/index.php?title=N-terminus&oldid=811323094 '' Categories : Posttranslational modification Proteins Protein structure Hidden categories : Articles needing additional references from January 2017 All articles needing additional references Talk Contents About Wikipedia Bosanski Català Čeština Dansk Deutsch Eesti Ελληνικά Español Français Galego Italiano עברית Nederlands 日本 語 Polski Português Русский Српски / srpski Srpskohrvatski / српскохрватски Svenska 中文 Edit links This page was last edited on 20 November 2017, at 22 : 08. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia ® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. About Wikipedia

Question: what is n and c terminus in protein
Answer: amino acids