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(or polysome), a protein-synthesizing complex in living cells; each complex is composed of one molecule of messenger ribonucleic acid (mRNA) and a few or several ribosomes connected to the mRNA molecule.
Polyribosomes are formed by the successive addition of ribosomes to mRNA. As they pass along the mRNA one by one, the ribosomes “read out” the information contained in the mRNA; it means that each ribosome synthesizes one molecule of protein (polypeptide chain) according to the program recorded in the mRNA. Protein synthesis in the cell is effected primarily by polyribosomes rather than by individual ribosomes.