Transcript Regulation of Gene Activity

Regulation of Gene Activity
Conservation
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Remember, our bodies are conservative, they
only make what we need, when we need it.
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How do they know this???
Operon
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Jacob and Monod – E. coli – capable of
regulating the expression of its genes
Regulator gene – codes for repressor
Repressor – controls whether the operon is
active or not.
Operon
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Promoter - DNA, beginning of gene to be
transcribed, signals the start of a gene
Operator – portion of DNA where repressor
binds, controls mRNA synthesis
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When repressor binds here, RNA polymerase
cannot attach to the promoter, prevents
transcription
Structural genes – codes for primary
structure of enzyme to be transcribed.
trp operon
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Exist in “on” position – repressible
Products – 5 different enzymes, synthesis of
AA tryptophan
If tryptophan is already present, it binds to
repressor, which then binds to operator and
no transcription takes place.
lac operon
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Makes 3 enzymes needed for metabolism of
lactose
When lactose is present, it binds to the
repressor, and repressor cannot bind to
operator, therefore transcription takes place
Lactose is an inducer, inducible operon
Eukaryotic regulation
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5 primary levels of control
Chromatin structure
Transcriptional control: transcriptional factors
initiate/regulate transcription
Posttranscriptional control: mRNA processing
and how fast mRNA leaves the nucleus
Translational control: when translation begins and
how long it continues
Posttranslational control: after protein synthesis,
polypeptide may have to undergo additional
changes before it is functional.
Chromatin structure
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Levels of chromatin organization is related to
the degree that the nucleosomes coil.
Heterochromatin – highly condensed
chromatin, inactive
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Barr Body- only in females, small, dark,
condensed chromatin, inactive
X chromosome
Euchromatin – loosely compacted chromatin,
potentially active, genes expressed.
Genetic mutations
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Point mutations – change in a single DNA
nucleotide, change in specific codon
Frameshift muations – one or more
nucleotides are inserted or deleted
Nonfunctional proteins – can have dramatic
effects on phenotype
carcinogenesis
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When proto-oncogenes mutate, they become
oncogenes.
Tumor suppressor genes usually act to stop
cell division if there is a problem.
Cancer – loss of TSG and activity of
oncogene = uncontrollable cell division