BIOLOGY - CLUTCH CH.18 - REGULATION OF...
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BIOLOGY - CLUTCH
CH.18 - REGULATION OF EXPRESSION
CONCEPT: BACTERIAL REGULATION OF EXPRESSION
● Transcriptional control – regulate ability of RNA polymerase to bind to a promoter and initiate transcription
● Translational control – regulate mRNA transcript degradation and translation initiation and elongation
● Post-translational control – activate or deactivate proteins
EXAMPLE:
● Negative control – a regulatory mechanism that prevents transcription, like “turning off” a gene
● Positive control – a regulatory mechanism that stimulates transcription, like “turning on” a gene
● Inducible systems – gene expression is normally stopped, but can be induced
● Repressible systems – gene expression is normally happening, but can repressed
EXAMPLE:
BIOLOGY - CLUTCH
CH.18 - REGULATION OF EXPRESSION
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CONCEPT: BACTERIAL REGULATION OF EXPRESSION
Operon – a cluster of genes under the control of a single promoter
□ Promoter – a region of DNA that initiates transcription
□ Operator – a segment of DNA to which transcription factors bind to regulate transcription
EXAMPLE:
● lac operon – an operon that allows for the transport and metabolism of lactose
□ lacI – a gene encoding a repressor protein for the lac operon
□ Repressor – a protein that binds to DNA and inhibits the expression of a gene, or set of genes
EXAMPLE:
● Lactose acts as and inducer, allowing for transcription of the lac operon.
EXAMPLE:
BIOLOGY - CLUTCH
CH.18 - REGULATION OF EXPRESSION
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CONCEPT: BACTERIAL REGULATION OF EXPRESSION
● The trp operon is normally “turned on”, giving the bacteria a steady supply of the amino acid tryptophan.
□ Tryptophan acts as a corepressor, activating the repressor protein.
EXAMPLE:
● Constitutive transcription – some genes are transcribed continuously
● Facultative transcription – some genes are only transcribed when needed
● Regulon – a group of genes or operons under the control of the same regulatory protein
EXAMPLE:
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CH.18 - REGULATION OF EXPRESSION
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CONCEPT: EUKARYOTIC REGULATION OF EXPRESSION
Eukaryotes can regulate their gene expression through the structure of DNA.
□ Nucleosome – a structure of 8 histone proteins around which DNA is wound
EXAMPLE:
● Histones can be acetylated, or deacetylated, to regulate gene expression.
EXAMPLE:
● DNA methylation – the addition of methyl groups to A and C in DNA as a form of regulation of gene expression
EXAMPLE:
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CH.18 - REGULATION OF EXPRESSION
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CONCEPT: EUKARYOTIC REGULATION OF EXPRESSION
Transcriptional regulation:
● Promoter-proximal elements – regulatory sites near promoters of genes, related genes use same regulatory molecules
● Basal transcription factors – general factors needed for transcription to occur that interact with the promoter
EXAMPLE:
● Transcription factors – activator and repressor proteins that bind to enhancers and silencers, respectively
● Enhancer – regulatory sequence that binds activator proteins
● Silencer – regulatory sequence that binds repressors
● Mediator proteins – act as a bridge between transcription factors and RNA polymerase
EXAMPLE:
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CH.18 - REGULATION OF EXPRESSION
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CONCEPT: EUKARYOTIC REGULATION OF EXPRESSION
RNA regulation:
● Alternative splicing – proteins interact with the spliceosome to determine which sequences will be spliced together
EXAMPLE:
● RNA interference – RNA held by a protein complex binds to mRNA causing its degradation, or preventing translation
□ miRNA (micro RNA) and siRNA (small interfering RNA) are the types of RNA involved in RNA interference
EXAMPLE:
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CH.18 - REGULATION OF EXPRESSION
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CONCEPT: EUKARYOTIC REGULATION OF EXPRESSION
Translational control generally involves initiation, but can also involve elongation and termination.
Post translational control:
● Folding – proteins must be folded, often with the assistance of chaperon proteins
● Chemical modification – many proteins are modified with non protein substituents
● Phosphorylation/dephosphorylation – act to regulate the activity of many proteins
EXAMPLE:
● Ubiquitin tagged proteins are marked for destruction by the proteasome
EXAMPLE:
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CH.18 - REGULATION OF EXPRESSION
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