Chapter 16 Regulation of Gene expression

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Chapter 16- Regulation of Gene expression

• Regulation is important!
• Regulation makes sense- the bacteria/cell does
  the logical, intelligent thing- so you can ask
  what would I do if I were a microbe?, and
  usually youll be right.
• Lots of wood/brick analogies, and stories.

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Some terms

• Inducible- the environmental effect (specific
  molecule) turns it on
• Constitutive- always on
• repressible- the environmental effect (specific
  molecule) turns it off.
• negative control- regulator turns it off.
• positive control regulator turns it on.

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Selected Bacterial Operons

• OPERON coordinately regulated genes, usually on
  the same mRNA in bacteria.
• By turning genes on and off in response to the
  environment, the cell works more efficiently,
  only making gene products needed at that time.
• Lac operon catabolism of lactose. 2 enzymes
  needed
• lac permease brings lactose in
• ß-galactosidase splits into glucose and
  galactose.
• Fuel.

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Control system fig 16-1-7 This is the situation
when no glucose is present, and lactose induces
the operon. Please study these figures!!!!
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Repressor acts negatively to inhibit
transcription. www.prenhall.com/klug
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Proof isolation and behavior of constitutive
mutants, such as Oc and lacI-, and
dominance/recessive behavior as merodiploids.
Table 16.1 Also biochemistry- isolation of
repressor protein, binding characteristics to
operator, etc.
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However, good repressor will work, so an I-/I
merodiploid will be regulated.
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A good operator will NOT work to restore
regulation!!
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A superrepressor (Is) will bind, shutting off
transcription, no matter what- it will be
dominant over an I
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CAP protein and positive regulation

• When glucose is in abundance, the lac operon is
  not turned on, even when lactose is present!
  Makes sense!
• Regulation involved CAP, cAMP, and RNA polymerase
• CAP catabolite activator protein stimulates
  transcription when cAMP levels are high.

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• cAMP Fig. 16-8 Formed when glucose levels are
  low. The enzyme that produces cAMP (adenyl
  cyclase), is inhibited by allosteric interaction
  with glucose. Thus as glucose levels fall, the
  enzyme is more active, cAMP levels rise.
• CAP cAMP bind to promoter, turns weak promoter
  into STRONG promoter!

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CAP is kind of like a transcription factor-
acting, stimulating transcription
CAP regulates probably 50 genes- NO sugar or
other carbon source would be used, as long as
glucose is there!
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Tryptophan biosynthesis

• Trp amino acid ( bricks) building block.
• trp operon genes for making tryptophan.
• trp is on when tryptophan levels are low off
  when levels are high.

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MORE allosteric interaction!
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Gene regulation in eukaryotes

• I. Some considerations (Fig. 16-12)
• a. lots more DNA chromatin has histones, which
  have to be considered. Chromatin can be
  available for transcription (decondensed) or
  unavailable (condensed), which makes a BIG
  difference!
• b. transcription in the nucleus, translation in
  the cytoplasm
• c. processing caps, tails, splicing.
• d. long half-life of mRNA in our cells! in
  bacteria, its about 3 min ours is 20 min or
  longer.
• e. cell differentiation not only environment,
  but cell type influences gene expression. (i.e.,
  no hairy livers!)

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