RIBOSOMES

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RIBOSOMES
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Discovery of Ribosomes

• Ribosomes first appeared under the electron
  microscope as dense granules.
• This discovery was made in the mid-1950s by
  Romanian cell biologist George Palade.

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Ribosome Synthesis

• Ribosomes are large ribonucleoproteins assembled
  from proteins and ribosomal RNA.
• In eukaryotic cells the manufacturing of
  ribosomes takes place in the nucleolus.
• Whereas in prokaryotes ribosomes are synthesised
  in the cytoplasm.

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Eukaryotic Ribosomes

• Eukaryotic ribosomes are larger than 70S
  ribosomes.
• The ribosome consists of two subunits (a large
  and a small) constructing an 80S particle.
• The larger 60S subunit and the smaller 40S
  subunit.

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Bacterial Ribosome

• Bacterial ribosomes have an overall Svedberg unit
  of 70S.
• Comprised of a large 50S subunit and a small 30S
  subunit.

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Image displaying translation taken from DNA the
secret of life Watson and Berry (2003) DNA the
secret of life.
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Translation

• mRNA template associates with small sub-unit.
• Ribosomes form peptide bonds between adjacent
  amino acids.
• The growing polypeptide chain leaves the ribosome
  through an exit tunnel in the body of the large
  subunit.

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Translation cont.

• The reaction continues until the ribosome meets a
  STOP codon.

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References

• Berg, J.M., Tymoczko, J.L., Stryer, L., 2006.
  Biochemistry. 6th Edition. New York W.H. Freeman
  And Company.
• Raven, P.H., Johnson, G.B, Mason, K.A, Losos, J.,
  Singer, S., 2008. Biology. 8th edition.
  BostonMcGraw Hill, Higher Education.