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Questions and Answers
Which of the following statements best describes cis-acting elements?
Which of the following statements best describes cis-acting elements?
The Lac repressor binds with high affinity to the lac operator when an inducer is present.
The Lac repressor binds with high affinity to the lac operator when an inducer is present.
False
What type of genetic element can influence the expression of a gene located on a different chromosome?
What type of genetic element can influence the expression of a gene located on a different chromosome?
Trans-acting genetic element
A major operator in the lac operon that is adjacent to the promoter is known as ____.
A major operator in the lac operon that is adjacent to the promoter is known as ____.
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Which of the following experiments involved genetic analysis of constitutive mutants in merodiploids?
Which of the following experiments involved genetic analysis of constitutive mutants in merodiploids?
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Match the following terms with their definitions:
Match the following terms with their definitions:
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How many lac operators exist in the lac operon?
How many lac operators exist in the lac operon?
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What is the role of the Lac repressor in relation to RNA polymerase binding?
What is the role of the Lac repressor in relation to RNA polymerase binding?
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The lacI mutant produces a functional repressor.
The lacI mutant produces a functional repressor.
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What mechanism do intrinsic terminators use to terminate transcription?
What mechanism do intrinsic terminators use to terminate transcription?
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ρ-dependent terminators work independently of other proteins.
ρ-dependent terminators work independently of other proteins.
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What are operons and why are they beneficial for bacterial gene expression?
What are operons and why are they beneficial for bacterial gene expression?
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The classic example of an operon is the ______ operon.
The classic example of an operon is the ______ operon.
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Match the following termination mechanisms with their characteristics:
Match the following termination mechanisms with their characteristics:
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What triggers the switch from metabolizing one sugar to another in diauxic growth?
What triggers the switch from metabolizing one sugar to another in diauxic growth?
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RNA polymerase travels from the 3' end to the 5' end of the DNA template during elongation.
RNA polymerase travels from the 3' end to the 5' end of the DNA template during elongation.
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E. coli needs to hydrolyze lactose into ______ to metabolize it.
E. coli needs to hydrolyze lactose into ______ to metabolize it.
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Which molecule signals low glucose levels for the regulation of the lac operon?
Which molecule signals low glucose levels for the regulation of the lac operon?
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The Lac repressor binds to all operator sequences simultaneously.
The Lac repressor binds to all operator sequences simultaneously.
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What is the role of the CRP-cAMP complex in the lac operon?
What is the role of the CRP-cAMP complex in the lac operon?
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The lac operon is negatively controlled by a repressor and positively controlled by the ______ complex.
The lac operon is negatively controlled by a repressor and positively controlled by the ______ complex.
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Match the following components with their functions in the lac operon:
Match the following components with their functions in the lac operon:
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What happens to cAMP levels when glucose is present?
What happens to cAMP levels when glucose is present?
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The presence of glucose enhances the expression of the lac operon.
The presence of glucose enhances the expression of the lac operon.
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Which genes are involved in arabinose utilization in E. coli?
Which genes are involved in arabinose utilization in E. coli?
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Study Notes
Prokaryotic Transcription
- Transcription is DNA-templated RNA synthesis
- Primary transcript is the immediate product of transcription in prokaryotes
- Pre-mRNA is processed to become mRNA in eukaryotes
- Ribonucleotides are added in a 5' to 3' direction, forming phosphodiester bonds
- RNA polymerase catalyzes RNA synthesis
- E. coli RNA polymerase has multiple subunits (σ, β, β', α, ω)
- σ subunit separates from core enzyme to form holoenzyme
- σ70 is a common σ subunit in E. coli
- Promoters are RNA polymerase binding sites
- Sigma factors and promoters can be studied using a filter binding assay
- Core enzyme and holoenzyme bind DNA differently; temperature affects binding
- Promoters have specific regions (e.g., -10 and -35) crucial for holoenzyme recognition.
- -10 region (Pribnow box) consensus sequence is TATAAT
- -35 region consensus sequence is TTGACA
- Mutations affecting promoter strength are called up or down mutations
DNase Footprinting
- Used to identify protein-DNA interactions
- Labeling, protein binding, then DNase treatment reveals binding sites
- Different sigma factors recognize different consensus sequences in core promoters
Transcription Stages
- Initiation: RNA polymerase binds to promoter, forms closed and open complexes, the σ subunit dissociates
- Elongation: RNA polymerase synthesizes RNA in a 5' to 3' direction
- Termination: Two types: Intrinsic (RNA polymerase pauses, forms hairpin loop) and Rho-dependent (Rho protein detaches RNA from polymerase)
Operons
- Operons group genes for related functions together for coordinated regulation
- The lac operon is an example of coordinated gene expression
- Diauxic growth is metabolizing preferred sugars first, then switching to second sugars
- Lac operon regulation depends on lactose (inducer) presence and levels of glucose
Lac Repressor
- Lac repressor is a homotetrameric protein
- Repressor has regulatory and DNA-binding domains
- Binds to the operator sequence when lactose is absent.
- Lactose, is converted to allolactose, which causes repressor to release, enabling transcription
Positive Control
- Cyclic AMP (cAMP) is a small metabolite related to low glucose
- cAMP receptor protein (CRP) binds cAMP
- CRP-cAMP complex binds to DNA and recruits RNA polymerase
- CRP-cAMP complex helps RNA polymerase bind promoters
Arabinose Operon
- Arabinose operon genes are coordinately regulated around an ara promoter
- AraC is a negative AND positive regulator.
- In absence of arabinose, AraC binds to DNA, looping it to block transcription
Galactose Operon
- Galactose operon has negative control, unlike Lac, which prevents the transition from closed to open complex preventing elongation
- Galactose is an alternative energy source for E. coli
Tryptophan Operon
- The trp operon controls the synthesis of tryptophan
- Operon expression is regulated negatively by tryptophan; when tryptophan is abundant, tryptophan binds repressor activating it (co-repressor).
- Attenuation of trp operon transcription can occur before polymerase reaches the tryptophan synthesis genes
Global Changes in Bacterial Transcription
- Sigma factors are crucial for RNA polymerase specificity
- Time-dependent programming occurs via switching sigma factors
- Sporulation and phage infection alter sigma factors for regulated gene expression
- Several specific sigma factors are needed for the sporulation process in Bacillus subtilis, enabling the expression of genes in certain phases of the process
Riboswitches
- Riboswitches are RNA molecules with small-molecule-binding elements that influence expression depending on the presence of ligand
Heat Shock Response
- Heat-shock response is rapid
- This is caused by the sigma factor 32 (RpoH) being free to bind, enabling transcription of heat shock proteins
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Description
Explore the mechanisms of prokaryotic transcription and the role of DNase footprinting in identifying protein-DNA interactions. This quiz covers key concepts such as RNA polymerase structure, promoter sequences, and the significance of sigma factors. Test your knowledge on these foundational topics in molecular biology.
