RNA could have served as both genetic material and as first enzymes in early life forms. Takes place in cytoplasm of eukaryotic cells. Translation is second step by which gene expression leads to protein synthesis. Amino acid-tRNA complex forms, then travels in cytoplasm to ribosome for protein synthesis. Subunits move separately through nuclear envelope pores into cytoplasm where they combine.
Ribosomes can float free in cytosol or attach to endoplasmic reticulum.
Polyribosomes are clusters of several ribosomes synthesizing the same protein. Nearly all polypeptides have signal sequences that target them for final location in cell. In translation, mRNA codons base-pair with tRNA anticodons carrying specific amino acids. Codon order determines order of tRNA molecules and sequence of amino acids in polypeptides. Protein synthesis involves chain initiation, chain elongation, chain termination.