Ribosomes are known as protein factory and are actively involved in the synthesis of protein. Ribosomes are found in the cytosol and in the semi-autonomous organelles, such as mitochondria and chloroplasts. Related Theory Ribosomes either occur singly (monosomes) or in cluster (polysomes). Apart from ribosomal RNA (rRNA), the other two forms of RNA required for protein synthesis are: messenger RNA (mRNA), which carries coding information from DNA, and transfer RNA (tRNA), which carries amino acids. Ribosomes use the information in mRNA to direct the synthesis of a protein. In prokaryotes, during proteins synthesis, many ribosomes line up and join the mRNA to form a string of ribosomes called polyribosome or polysome.