Wednesday, February 4, 2009


Ribosomes are the protein-synthesizing organelles of the cell. Ribosomes are about 20nm in diameter and are composed of 65% ribosomal RNA and 35% ribosomal proteins, known as a Ribonucleoprotein or RNP. Free ribosomes are suspended in the cytosol, which is the semi-fluid portion of the cytoplasm; others are bound to the rough endoplasmic reticulum, giving it the appearance of roughness and thus its name.

The ribosome functions in the expression of the genetic code from nucleic acid into protein, in a process called translation. Ribosomes do this by catalyzing the assembly of individual amino acids into polypeptide chains; this involves binding a messenger RNA and then using this as a template to join together the correct sequence of amino acids.

Ribosomes were first observed in the mid-1950s by Romanian cell biologist George Palade using an electron microscope as dense particles or granules for which he would win the Nobel Prize. The term "ribosome" was proposed by scientist Richard B. Roberts in 1958.