Regulcia expresie v prokaryotoch

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Lac operón

• Regulácia expresie v prokaryotoch
• Jacobov Monodov model

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• Promoter is the DNA region where the
  transcription initiation takes place. 
• In prokaryotes, the sequence of a promoter is
  recognized by the Sigma (?) factor of the RNA
  polymerase. 
• In eukaryotes, it is recognized by specific
  transcription factors.

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 E. coli operons.  An operon consists of several
genes which are transcribed together.(a) The lac
operon comprises lacA, lacY and lacZ.  The lacI
gene is not part of the operon, but encodes a
protein which could repress transcription of the
lac operon.  (b) The trp operon consists of
trpA, trpB, trpC, trpD, and trpE.  (Numbers
represent the genome sequence).
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• It was in 1953 that Watson and Crick, on the
  basis of observations made by Chargaff and
  Wilkins, proposed their model of the structure of
  DNA. From the first, in this complementary double
  sequence,one could see a mechanism for exact
  replication of the genetic material. Meanwhile,
  one year earlier, Sanger had described the
  peptide sequence of insulin, and it was also
  already known, from the work of Pauling and Itano
  in particular, that a genetic mutation can cause
  a limited modification in the structure of a
  protein.
• In 1954, Crick and Watson and Gamow proposed the
  genetic code theory The primary structure of
  proteins is determined and defined by the linear
  sequence of the nucleotides in DNA. Thus the
  profound logical intuition of Watson and Crick
  had allowed them to discover a structure that
  immediately explained, at least in principle, the
  two essential functions long assigned by
  geneticists to hereditary factors to control its
  own synthesis and to control that of the
  nongenetic constituents. Molecular biology had
  been born, and I realized that, like Monsieur
  Jourdain, I had been doing molecular biology for
  a long time without knowing it.

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In the words of his friend and colleague, Melvin
Cohn, Jacques Monod had one of the most creative
minds of our time, but not because he was a
leader of righteous causes, a creator of
molecular biology, or a founder and director of
an institute of learning. He had one of the most
creative minds simply because he thought deeply
and ascetically, and in a Socratic way, about how
knowledge is acquired, and it is this process
that he insisted should be the only basis for a
system of ethical and aesthetic values.
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All proposals of the operon model were verified
in every detail. The hunt for the repressor was
successful. Gilbert and Muller-Hill managed to
purify the repressor protein in 1967 by using its
affinity to radioactively labeled IPTG. With the
protein in hand, the operator DNA it binds with
could be fished out. Gilbert and Maxam developed
the art of chemical sequencing of DNA primarily
to determine the lac operator sequence.The
genetic code was determined the same year the
operon model was proposed. Molecular biology has
becoming a flourishing science. For their
monumental contributions in the area of gene
regulation, Monod and Jacob shared the Nobel
Prize in 1965 along with Andre Lwoff, Monods
mentor.
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