Ribosomes

"Protein factories" in cells

Ribosomes are the smallest of all sub-cellular organelles, only visible under an electron microscope.

A single E. coli bacterium has about 15,000 ribosomes.

When genes are expressed in cells, the DNA sequence encoding the gene is transferred to a mobile strand of RNA (messenger RNA, mRNA). When the mRNA reaches a ribosomone, the sequence is translated one amino acid at a time into a polypeptide chain that forms a protein.