Computer artwork of a ribosome. Ribosomes are protein particles that are found in cell cytoplasm. Each ribosome has a large and a small subunit. Messenger ribonucleic acid passes between the two subunits and provides the instructions for the assembly of a protein (polypeptide) chain from amino acids. The mRNA originates in the cell's nucleus, and is a copy of the information coded in DNA (deoxyribonucleic acid). The process of protein synthesis from mRNA in ribosomes is known as translation. Different sequences of mRNA produce different proteins.