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What metabolizes Lactose?
beta-galactosidase
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Allolactose signals what?
lacZ and beta-galatosidase expression
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Cause for temporary pause in growth in bacteria when media is shifted?
- Glucose is in initial plate, so bacteria uses glucose, does not express lactose genes because it is unnessecary
- Switched to lactose plate, need to be able to process lactose
- Allolactose promotes lacZ and results in in expression in form of beta-galactosidase
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What controls enzymes levels
Molecular regulation of gene expression
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Induction versus Repression
- Induction is turning on gene in presence of a molecular signal
- Repression is turning off a gene in presence of a molecular signal
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Promoters integrate what kinds of signals.
+ and -
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Repressor proteins stop gene expression by:
binding the promoter and preventing the RNAP from binding (steric competition)
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Allagalactose promotes expression by:
Binding to the repressor protein and preventing it from binding promoter
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How does glucose decrease result in beta-galactosidase expression
- As glucose decreses cAMP increase
- cAMP binds CAP (CRP cAMP Receptor Protein)
- cAMP+CAMP interact with RNAP to stimulate gene expression
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Negative Regulation
- Repressor bound to promoter inhibits transcription
- Ligand binds to and removes repressor
- Likewise, a ligand bind may result in the repressor binding to promoter and turning it off
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Positive Regulation
- Bound activator protein promotes transcription
- Ligand binds removes activator and prevents gene transcription
- Similarly, ligand binding may result in activator binding promoter and turning it on
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Lac operon is a ___ system
Induction
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Regulators can be close or far from the gene
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DNA looping
proteins bound distally cooperate with proteins found closer
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Basic principles of expression are __, but molecularly ___
conserved, diverse
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Transcriptonal regulators directly influence:
initiation complex assembly and stability.
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Transcription domains essential for
promoting transcription
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Means of regulation for gene expression
- Constitutive expression: some genes are mostly always on at same level
- Developmental gene regulation: some genes undergo long-lasting changes in expression in response to intracellular and/or extracellular signals
- Cell cycle gene regulation: some genes turned on at specific steps of cell cycle.
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How do proteins recognize specific DNA sequence
- Amino acid side chains contact functional groups in nucleotide bases (polypeptide motifs)
- Proteins form H-bonds with nucleotide bases
- Most bind in the major, not minor groove
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