Transcript REGULATION OF GENE EXPRESSION

REGULATION OF GENE EXPRESSION
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Gene Interactions
The simplest form of gene interaction: Dominant vs. recessive
Incomplete Dominance
Josef Kolreuter: white/red carnations yielded pink
colors are not blended; F-2 generation had a reappearance
The active allele doesn’t compensate for the inactive allele
Codominance
Both alleles are expressed (active)
Roan cattle and erminette chickens
Written with both capital letters
Polygenic Inheritance
Traits controlled by two or more genes
Color of hair and eyes, shape and size of the nose
GENE EXPRESSION
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GENE EXPRESSION IN
PROKARYOTES
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THE OPERON
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Francois Jacob & Jacques Monod
Regions involved in the regulation and expression of nearby gene
clusters.
Three Parts
a cluster of genes working together
a region of the chromosome near the cluster: operator
a region of the chromosome next to the operator: promotor
products that initiates the production of enzymes are inducers
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THE REPRESSOR
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Protein responsible for turning “off” the operon
See fig. 10-18
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GENE ACTIVATION
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binds to repressor; repressor falls off the operator (fig. 10-19)
RNA polymerase binds to promotor, moves across to the genes, &
produces mRNA. When cell runs out of the inducer, repressor binds to
operator, and the operator is turned off.
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GENE EXPRESSION IN
EUKARYOTES
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Inducers also active in eukaryotes
1976 Philip Sharp and Susan Berget
mRNA produced during transcription may be altered before it is
used to make proteins during translation.
Exons: “Expressed” sequences that are a complementary code
for proteins.
Introns: “Intervening” sequences that are not a complementary
code for proteins.
RNA moves along a gene, it transcribes the entire gene, so premRNA contains introns.
Before protein can be produced, the pre-mRNA must be processes
into functional mRNA
The introns are removed and the exons are spliced back together
The mRNA must complete this process before it leaves the
nucleus
See fig. 10-21