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12-5 GENE REGULATION
1. Gene Regulation: An Example
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E. Coli (bacteria) gives a good example of how
genes are able to regulate being expressed
Operon- a group of genes that operate (work)
together
 E.
Coli use lactose (milk sugar) as a food source
 To eat the lactose the genes to eat the sugar must be
turned on
 Lac Operon- genes that allow E. coli to eat lactose
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Repressor- turn off genes
Operator- area of a chromosome in an operon that the
repressor binds to when the operon is “turned off”
Lac genes are turned off by the repressor
Lac genes are turned on by the presence of lactose
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Many genes are regulated by repressor proteins
Some genes use proteins that speed transcription.
Sometimes regulation occurs at the level of protein
synthesis.
2. Eukaryotic Gene Regulation
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Operons are not found in eukaryotic organisms
…..but…
Most eukaryotic genes are controlled individually
and have regulatory sequences that are much more
complex than those of the lac operon.
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TATA Box- a short region of DNA that helps start
transcription
Helps RNA polymerase bind to DNA
3. Development and differentiation
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Differentiation- as cells grow & divide they become
specialized in structure and function with the help of
hox genes
Hox genes- control the differentiation of cells and
tissues in the embryo
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Careful control of expression in hox genes is
essential for normal development
All hox genes are descended from the genes of
common ancestors.