Ch. 18 Regulation of Gene Expression Objectives: LO 3.18 The student is able to describe the connection between the regulation of gene expression and observed differences between different kinds of organisms. LO 3.19 The student is able to describe the connection between the regulation of gene expression and observed differences between individuals in a population. LO 3.20 The student is able to explain how the regulation of gene expression is essential for the processes and structures that support efficient cell function. LO 3.21 The student can use representations to describe how gene regulation influences cell products and function. LO 3.22 The student is able to explain how signal pathways mediate gene expression, including how this process can affect protein production..
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Ch. 18 Regulation of Gene Expression Objectives: LO 3.18 The student is able to describe the connection between the regulation of gene expression and observed.
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Ch. 18 Regulation of Gene Expression
Objectives:
LO 3.18 The student is able to describe the connection between the regulation of gene expression and observed differences between different kinds of organisms.LO 3.19 The student is able to describe the connection between the regulation of gene expression and observed differences between individuals in a population.LO 3.20 The student is able to explain how the regulation of gene expression is essential for the processes and structures that support efficient cell function.LO 3.21 The student can use representations to describe how gene regulation influences cell products and function.LO 3.22 The student is able to explain how signal pathways mediate gene expression, including how this process can affect protein production..LO 3.23 The student can use representations to describe mechanisms of the regulation of gene expression.
18.1 Bacteria Often Respond to Environmental Change by Regulating Transcription
Conserve resources 1 of 2 ways:• Feedback inhibition (discussed in Ch. 8)• Regulation of gene expression (discussed here)
Precursor
Feedbackinhibition
Enzyme 1
Enzyme 2
Enzyme 3
Tryptophan
(a) (b)Regulation of enzymeactivity
Regulation of enzymeproduction
Regulationof geneexpression
trpE gene
trpD gene
trpC gene
trpB gene
trpA gene
Operons: The Basic Concept and Negative Gene Regulation
Operons:• Operator (“on/off switch”), promoter, and genes.
– Repressible (anabolic) operons: Always “on” until repressor is bound. (inhibited)
• Corepressor is like feedback inhibition (product works with repressor)• Ex: tryptophan producing genes
Promoter
DNA
Regulatory genemRNA
trpR
5
3
Protein Inactive repressor
RNApolymerase
Promoter
trp operon
Genes of operon
Operator
mRNA 5Start codon Stop codon
trpE trpD trpC trpB trpA
E D C B A
Polypeptide subunits that make upenzymes for tryptophan synthesis
(a) Tryptophan absent, repressor inactive, operon on
(b) Tryptophan present, repressor active, operon off
DNA
mRNA
Protein
Tryptophan (corepressor)
Activerepressor
No RNAmade
• Inducible (catabolic) operons are usually off but can be induced.– Inducer inactivates the repressor– Ex: lac (lactose) operon
(a) Lactose absent, repressor active, operon off
(b) Lactose present, repressor inactive, operon on
Regulatorygene
Promoter
Operator
DNA lacZlacI
lacI
DNA
mRNA5
3
NoRNAmade
RNApolymerase
ActiverepressorProtein
lac operon
lacZ lacY lacADNA
mRNA
5
3
Protein
mRNA 5
Inactiverepressor
RNA polymerase
Allolactose(inducer)
-Galactosidase Permease Transacetylase
Positive Gene Regulation
• Gene is always on but activator stimulates transcription.– Ex: cAMP
Animation: Protein ProcessingRight-click slide / select “Play”
18.3 Noncoding RNAs Play Multiple Roles in Controlling Gene Expression
• Parts of DNA that make very small RNA (ncRNA) but not proteins; regulate gene expression.– Bind to a complementary sequence of mRNA, blocking translation.– Bind to DNA changing chromatin structure1. microRNAs (miRNA): begins as hairpin2. Small interfering RNAs (siRNA): begins as double strand
(a) Primary miRNA transcript
HairpinmiRNA
miRNA
Hydrogenbond
Dicer
miRNA-proteincomplex
mRNA degraded Translation blocked(b) Generation and function of miRNAs
5 3
18.4 A Program of Differential Gene Expression Leads to the Different Cell Types in a Multicellular Organism