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Control of gene expression
Negative control: when regulatory protein is attached then
transcription is stopped
Positive control: when regulatory protein is attached
transcription is enhanced
Induction: signal from environment induces transcription
Repression: signal from environment stops transcription
Control of gene expression
Induction
Example
Repression
Example
Positive
Expression enhanced
Negative
Expression turned on
Lac Operon
Expression not enhanced
Glucose inhibits Lac Op.
Expression turned off
Tryp Operon
Fig. 19.7
Levels of control of gene expression in Eukaryotes
Fig 19.7
Fig. 19.1
Levels of DNA packing
Barr bodies - highly methylated mammalian X-chromosomes
A polytene chromosome from a Drosophila salivary gland
Patterns of control of gene expression
Negative control - an active regulatory protein turns
transcription OFF
Induction - signal molecule turns the operon on
Repression - signal molecule turns the operon off
Positive control - an active regulatory protein enhances the rate
Of transcription
Induction - signal molecule makes the regulatory protein active
Repression - signal molecule makes the regulatory protein inactive
Fig. 17.7
Details of transcription in Eukaryotes
Different cell types
(e.g. brain versus liver
cells) have different
sets of transcription
factors.
Fig. 19.8
Control elements - DNA sequences that react with
proteins to facilitate the binding of RNA polymerase
Fig. 19.9
Interaction between activator proteins,
enhancer sequences, and transcription factors
Different regions of genome can share the same regulatory
elements turnings groups of genes on or off simultaneously
Gene 1
Gene 2
Gene 3
Fig 19.11
Fig 19.7
Fig. 19.7
Levels of control of gene expression in Eukaryotes