The Genetic Code

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The Genetic Code Transcription and Translation

• Lecture 9

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Transcription Copying DNA into RNA
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Sigma Factors

• The initiation of transcription is an especially
  important step in gene expression because it is
  the main point at which the cell regulates which
  proteins are to be produced and at what rate.
  Bacterial RNA polymerase is a multisubunit
  complex. A detachable subunit, called sigma (s)
  factor, is largely responsible for its ability to
  read the signals in the DNA that tell it where to
  begin transcribing. RNA polymerase molecules
  adhere only weakly to the bacterial DNA when they
  collide with it, and a polymerase molecule
  typically slides rapidly along the long DNA
  molecule until it dissociates again. However,
  when the polymerase slides into a region on the
  DNA double helix called a promoter, a special
  sequence of nucleotides indicating the starting
  point for RNA synthesis, it binds tightly to it.
  The polymerase, using its s factor, recognizes
  this DNA sequence by making specific contacts
  with the portions of the bases that are exposed
  on the outside of the helix.

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Transcription of two genes as observed under the
electron microscope.
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Transcription Copying DNA into RNA
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tRNA or Transfer RNA
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Translation

• AUG AAA GGC CCC UAG

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Ribosome is a complex of protein and rRNA or
ribosomal RNA
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Translation

• ATG AAA CGC CCC TAG - DNA
• AUG AAA CGC CCC UAG
• Met Lys Arg Pro Stop

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The Genetic Code
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The End