translasiooni

Translatsioon, or translaatsiooni in some contexts, refers to the cellular process of protein synthesis in which ribosomes decode messenger RNA (mRNA) to produce polypeptide chains. The process is central to gene expression and occurs in the cytoplasm of cells, in some eukaryotes on the endoplasmic reticulum, and in prokaryotes within the cytosol.

Mechanism and stages

Translatsioon proceeds through three main stages: initiation, elongation, and termination. Initiation begins when the ribosome assembles at the start codon on the mRNA, with a initiator tRNA carrying methionine (in eukaryotes) or formylmethionine (in bacteria) and various initiation factors facilitating assembly. During elongation, aminoacyl-tRNA molecules pair with codons on the mRNA within the ribosome’s decoding site, peptide bonds form to extend the growing polypeptide, and the ribosome translocates along the mRNA in a 5' to 3' direction. Termination occurs when a stop codon is reached and release factors promote release of the finished polypeptide, after which the ribosomal subunits disengage.

Regulation and variation

Translation is tightly regulated at multiple levels, including initiation control by initiation factors, availability of ribosomes and tRNAs, and signaling pathways such as mTOR. In some cells, translation is organized into polysomes to increase efficiency. Examples of variation include internal ribosome entry sites (IRES) that allow cap-independent initiation and differences between prokaryotic and eukaryotic initiation mechanisms.

Significance

Translatsioon is essential for cellular function and organismal development. Proper regulation ensures proteome balance, while defects in translation can contribute to disease and stress responses. The study of translatsioon encompasses topics from basic molecular biology to disease mechanisms and therapeutics.