They are spherical structures about 10nm

    in length and 10-15nm in width

  They are dark and round

  They are made up of protein [40%] and 

    ribonucleic acid (RNA) [60%] 

They may attach to ER or occur freely 

    in the cytoplasm

Each of them consists of two subunits 

    --- one large and one small

     Structure of ribosome 

A number of them moving simultaneously 

   along the mRNA, like beads on a string. 

   The resulting chains of them are called 

   polyribosomes or polysomes

Ribosomes and Polyribosomes ( Liver Cell ) 

They manufacture protein according to 

     the genetic information coded in the

     messenger RNA (mRNA)