What is a ribosome?
A Ribosome is a cell structure that uses genetic instructions transported in ribonucleic acid (RNA) to link a specific sequence of amino acids into chains to form proteins. These organelles are pretty small, made up of fifty proteins and several long RNA strands bound together.
http://www.sciam.com/explorations/1999/092799ribo/
Where are ribosomes found?
Ribosomes are found dispersed in the cytoplasm of all prokaryotic cells: bacteria. They are also found in the cytoplasm of eukaryotic cells: protists, fungi, plants, and animals, where they are either free to float in the cytoplasm or are bound to networks of endoplasmic reticulum which are membrane-enclosed tubules in the cytoplasm. Also, in eukaryotic cells, two types of cell structures called mitochondria and chloroplasts contain ribosomes.
black dots represent ribosomes on the rough ER
http://esg-www.mit.edu:8001/esgbio/cb/organelles.html
Do ribosomes have membranes?
Ribosomes have no membrane. Ribosomes disassemble into two subunits when not actively synthesizing protein.
Ribosomes in prokaryotic and eukaryotic cells
Ribosomes in the cytoplasm of prokaryotic and eukaryotic cells slightly differ. Prokaryotic ribosomes are smaller and less dense and each contain only three strands of RNA and about fifty proteins. Eukaryotic ribosomes consist of four strands of RNA and contain seventy to eighty proteins. The ribosomes in mitochondria and chloroplasts resemble prokaryotic ribosomes.
What is the function of a ribosome?
Ribosomes are the sites of protein synthesis, where RNA is translated into protein. When cells need large numbers of proteins, they must first build numerous ribosomes. Because protein synthesis is so important to cells, there are large numbers of ribosomes found throughout cells often numbering in the hundreds or thousands. In eukaryotic cells, three of the four ribosomal RNA strands are synthesized in the nucleolus, a structure in the nucleus. The fourth ribosomal RNA strand is synthesized outside of the nucleolus and then transported into the nucleolus for ribosome assembly. Ribosomal proteins enter the nucleolus and combine with the four ribosomal RNA strands to create the large and small subunits which are two ribosomal structures. The two subunits unite outside the nucleus just before the ribosome begins to manufacture proteins. Prokaryotic cells lack a nucleus or nucleolus and therefor ribosomal synthesis takes place in the cytoplasms. Without the ribosomes the message would not be read and proteins could not be produced.
http://web.mit.edu/esgbio/www/dogma/trl.html
http://www.sciam.com/explorations/1999/092799ribo/
RIBOSOMES, made up of two subunits (gray and
violet), ride along threads of messenger or mRNA
(yellow), translating genetic information (above).
Codons--stretches of three amino acids--on the mRNA are
matched up with complementary anticodons on transfer
RNAs (green and pink), thereby forming the polypeptide
chains (navy squares) used to build proteins. New detailed
images of ribosomes (below) have revealed how the
three binding sites for tRNAs (green, pink and blue) act
as a conveyor belt, as well as other mechanical aspects of
protein formation.
By:Lindsey Volckmann 2-16-00