Structure of the Ribosome

• They are the most numerous organelles in almost all cells
• Ribosomes are from 15 to 20 milimicrons in diameter (i.e. very small)
• Ribosomes are made up of structural proteins and ribonucleic acid(RNA).   (This RNA is special, and is only used in ribosomes.  It is called "Ribosomal RNA")
• A ribosome is made of about 40% protein and 60 % nucleic acid. It is composed of four nucleic acid molecules and about 70 different proteins.
• These molecules are arranged into two subunits called the large and small subunits. These subunits are attached to each other and together form the entire ribosome.
• When viewed through a light microscope the ribosomes appear as rounded dots, since they are very small and the subunits can not be seen. 
  

Functions of the Ribosome

• Ribosomes are the location of amino-acid assembly withen the cell
• The more Ribosomes within a given cell, the more protein production there is within the cell
  

Ribosome are either free-floating within the cell, or attached to the Endoplasmic Reticulum (ER)

If Attached to the ER:

• These ribosomes make enzyme proteins (such as digestive enzymes)
• They occur in greater number than free ribosomes in cells that secrete their manufactured proteins (e.g., pancreatic cells, producers of digestive enzymes)
  
• They are responsible for proteins that become a part of membranes or packaged into vesicles for storage in the cytoplasm or export to the cell exterior
  

If Within the Cytoplasm:

• The ribosomes make structural proteins and other necessary proteins such as hemoglobin
• In rapidly growing cells, they are scattered in small clusters of 5 or 10 throughout the cytoplasm
• They may occur as a single ribosome or in groups known as polyribosomes or polysomes
  
• In cells that retain most of their manufactured protein, free ribosomes occur in greater number than bound ribosomes  
• They are responsible for proteins that go into solution in the cytoplasm or form important cytoplasmic structural or motile elements
  

Cited Information
http://www.howe.k12.ok.us/~jimaskew/bcell1.htm
        A comprehensive site, detailing the basic model of a cell and its constituent organelles, contains lots of basic information on ribosomal structure and functions.
Biology by Helena Curtis/worth publishers/1968/New York, New York
    A Biology text, its section of the ribosome included information on ribosomal structure and the part ribosomes play in protein synthesis.
http://cellbio.utmb.edu/cellbio/ribosome.htm
     A website debevoted to the Ribosome.  Contains basic information on the structure and function of ribosomes as well as a detailed explanation of Ribosomal protein synthesis.
http://www.aip.org/physnews/graphics/html/ribosome.html
       This small site contains a graphic image of a ribosome and some information on current ribosomal research.
http://www.historyoftheuniverse.com/ribosome.html
       This page, part of a much larger website, contains some very basic information on ribosomal structure and function.