The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or amine-terminus) refers to the end of a protein or polypeptide terminated by an amino acid with a free amine group (-NH2). Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Peptides (from the Greek πεπτίδια, "small digestibles" are short Polymers formed from the linking in a defined order of α- Amino In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this Amines are Organic compounds and Functional groups that contain a basic Nitrogen Atom with a Lone pair. The convention for writing peptide sequences is to put the N-terminus on the left and write the sequence from N- to C-terminus. The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal end, or When the protein is translated from messenger RNA, it is created from N-terminus to C-terminus.
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Chemistry
Each amino acid has a carboxyl group and an amine group, and amino acids link to one another to form a chain by a dehydration reaction by joining the amine group of one amino acid to the carboxyl group of the next. Carboxyl group or CO2H is a Functional group present in Amino acids and Carboxylic acids Its structure is composed of one carbon atom attached In Chemistry, a dehydration reaction is usually defined as a chemical reaction that involves the loss of water from the reacting molecule Thus polypeptide chains have an end with an unbound carboxyl group, the C-terminus, and an end with an amine group, the N-terminus. The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal end, or
When the protein is translated from messenger RNA, it is created from N-terminus to C-terminus. Translation is the first stage of Protein biosynthesis (part of the overall process of Gene expression) Messenger ribonucleic acid ( mRNA) is a molecule of RNA encoding a chemical "blueprint" for a Protein product 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 or nascent chain. Transfer RNA (abbreviated tRNA) is a small RNA (usually about 74-95 nucleotides that transfers a specific Amino acid to a growing polypeptide chain at Since the start codon of the genetic code codes for the amino acid methionine, most protein sequences start with a methionine (more specifically: the modified version N-formylmethionine, fMet). ATG and AUG denote sequences of DNA and RNA respectively that are the Start codon or initiation Codon encoding the Amino acid The genetic code is the set of rules by which information encoded in genetic material ( DNA or RNA sequences is translated into Proteins Methionine ( abbreviated as Met or M) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH2CH2SCH3 N -Formylmethionine (fMet is an Amino acid found in all living cells It is a derivative of the Amino acid Methionine in which 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. Posttranslational modification (PTM is the chemical modification of a Protein after its translation. A protein precursor, also called a pro-protein or pro-peptide, is an inactive Protein (or Peptide) that can be turned into an active form by
Function
N-terminal targeting signals
The N-terminus is the first part of the protein that exits the ribosome during protein biosynthesis. Ribosomes ( from ribo nucleic acid and "Greek soma ( meaning body") are complexes of RNA and Protein that Protein biosynthesis (synthesis is the process in which cells build Proteins The term is sometimes used to refer only to protein translation but more It often contains sequences that act as targeting signals, basically intracellular zip codes, that allow for the protein to be delivered to its designated location within the cell. The ZIP code is the system of Postal codes used by the United States Postal Service (USPS The targeting signal is usually cleaved off after successful targeting by a processing peptidase
- 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. A protease is any Enzyme that conducts Proteolysis, that is begins protein Catabolism by Hydrolysis of the Peptide bonds that link A signal peptide is a short (3-60 Amino acids long Peptide chain that directs the post- translational transport of a Protein. The signal recognition particle (SRP is a Ribonucleoprotein ( Protein - RNA complex that recognizes and transports specific proteins to the Endoplasmic The secretory pathway is a series of steps a cell uses to move Proteins out of the cell a process known as secretion. In eukaryotic cells, these proteins are synthesized at the rough endoplasmic reticulum. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex The endoplasmic reticulum (Greek endo = "within" (prefix plásma = "formed entity" Latin reticulum = "little net" or ER, is an Organelle In prokaryotic cells, the proteins are exported across the cell membrane. The prokaryotes (proʊˈkærioʊts singular prokaryote /proʊˈkæriət/ are a group of Organisms that lack a Cell nucleus (= karyon or any other The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer In chloroplasts, signal peptides target proteins to the thylakoids. Chloroplasts are Organelles found in Plant cells and eukaryotic Algae that conduct Photosynthesis. A Thylakoid is a membrane-bound compartment inside Chloroplasts and cyanobacteria.
- Mitochondrial targeting peptide
The N-terminal mitochondrial targeting peptide (mtTP) allows for the protein to be imported into the mitochondrion. In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells.
- Chloroplast targeting peptide
The N-terminal chloroplast targeting peptide (cpTP) allows for the protein to be imported into the chloroplast. Chloroplasts are Organelles found in Plant cells and eukaryotic Algae that conduct Photosynthesis.
N-terminal modifications
Some proteins are modified posttranslationally by the addition of membrane anchors that allow the protein to associate with membrane without having a transmembrane domain. Transmembrane domain usually denotes a single transmembrane Alpha helix of a Transmembrane protein. The N-terminus (as well as the C-terminus) of a protein can be modified this way. The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal end, or
- N-Myristoylation
The N-terminus can be modified by the addition of a myristoyl anchor. Myristoylation is an irreversible co-translational (during translation Protein modification found in Animals Plants Fungi and Viruses Myristic acid, also called tetradecanoic acid, is a common saturated Fatty acid with the molecular formula CH3(CH212COOH Proteins that are modified this way contain a consensus motif at their N-terminus as a modification signal.
- N-Acylation
The N-terminus can also be modified by the addition of a fatty acid anchor to form N-acylated proteins. S-Palmitoylation is the covalent attachment of fatty acids such as Palmitic acid, to Cysteine residues of membrane proteins In Chemistry, especially Biochemistry, a fatty acid is a Carboxylic acid often with a long unbranched Aliphatic tail ( chain) which The most common form of such modification is the addition of a palmitoyl group. S-Palmitoylation is the covalent attachment of fatty acids such as Palmitic acid, to Cysteine residues of membrane proteins
See also
References
The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal end, orDapyx Software network: MP3 Explorer | Ebook Manager | Zenithic