Biochem 501: Part IV.7: Gene Regulation
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What metabolizes Lactose?
Allolactose signals what?
lacZ and beta-galatosidase expression
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
What controls enzymes levels
Molecular regulation of gene expression
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
Promoters integrate what kinds of signals.
+ and -
Repressor proteins stop gene expression by:
binding the promoter and preventing the RNAP from binding (steric competition)
Allagalactose promotes expression by:
Binding to the repressor protein and preventing it from binding promoter
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
- 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
- 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
Lac operon is a ___ system
Regulators can be close or far from the gene
proteins bound distally cooperate with proteins found closer
Basic principles of expression are __, but molecularly ___
Transcriptonal regulators directly influence:
initiation complex assembly and stability.
Transcription domains essential for
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.
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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