| A ribosome is a small, dense organelle in cells that assembles proteins. Ribosomes are about 20nm in diameter and are composed of 65% ribosomal RNA and 35% ribosomal proteins (known as a Ribonucleoprotein or RNP). It translates messenger RNA (mRNA) to build a polypeptide chain (e.g., a protein) using amino acids delivered by Transfer RNA (tRNA). It can be thought of as a giant enzyme but, although it contains proteins, its active site is made of RNA, so ribosomes are now classified as "ribozymes".[1] Ribosomes build proteins from the genetic instructions held within a messenger RNA. Free ribosomes are suspended in the cytosol (the semi-fluid portion of the cytoplasm) or bound to the rough endoplasmic reticulum, or to the nuclear envelope. Since ribosomes are ribozymes, it is thought that they might be remnants of the RNA world.[2] While catalysis of the peptide bond involves the C2' hydroxyl of tRNA's P-site adenosine in a sort of proton shuttle mechanism, the full function (ie, translocation) of the ribosome is reliant on changes in protein conformations. Ribosomes are an important structure in the cell. Ribosomes were first observed in the mid-1950s by Romanian cell biologist George Palade in the electron microscope as dense particles or granules[3] for which he would win the Nobel Prize. |
