polypeptide rna has an amino acid attached and is used in the formation of a peptide chain.
polypeptide rna has an amino acid attached and is used in the formation of a peptide chain.
what type of rna has an amino acid attached and is used in the formation of a peptide chain?
polypeptide
ribosomes have two subunits, one large and one small. these subunits surround the mrna strand. the larger subunit contains three binding sites: a (aminoacyl), p (peptidyl), and e (exit). after translational initiation (which is different in prokaryotes and eukaryotes), the ribosome enters the elongation period which follows a repetitive cycle. first a trna with the correct amino acid enters the a site. the ribosome transfers the peptide from the trna in the p site to the new amino acid on the trna in the a site. the trna from the p site will be shifted into the e site where it will be ejected. this continually occurs until the ribosome reaches a stop codon or receives a signal to stop. a peptide bond forms between the amino acid attached to the trna in the p site and the amino acid attached to a trna in the a site. the formation of a peptide bond requires an input of energy. the two reacting molecules are the alpha amino group of one amino acid and the alpha carboxyl group of the other amino acids. a by-product of this bond formation is the release of water (the amino group donates a proton while the carboxyl group donates a hydroxyl).
protein metabolism
each module performs all the catalytic reactions necessary to incorporate a single amino acid onto the peptide chain. this is accomplished through the subdomains for adenylation (a), peptityl carrier protein (pcp), condensation (c), and depending on the amino acid position, an epimerization (e). the adenylation subdomain is used in activating the specific amino acid. each module uses one molecule of the selected substrate amino acid with one molecule of atp to give an aminoacyl adenylate enzyme complex and pyrophosphate. the activated amino acid can then be transferred to the enzyme bound 4'-phosphopantetheine of the carrier protein with the expulsion of amp from the system. the carrier protein uses the 4'-phosphopantetheine prosthetic group for loading of the growing peptide and their monomer precursors. elongation of the peptide chain is achieved through condensation of the upstream pcp onto an adjacent downstream pcp-bound monomer. in certain domains you will find modification subdomains, such as the e subdomain seen in domains 1 and 4 in tyrocidine, which will generate the d-configured amino acid. on the final module is the te domain used as a catalyst for cyclization or product release. the release of the product from the carrier protein is achieved through acylation of the active site serine of te in which the decapeptide is transferred from the thiol ether to the serine residue. deacylation can then occur through intramolecular cyclization or through hydrolysis to give the cyclic or linear product respectively (see figure 4).
tyrocidine