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Questions and Answers
Which segment of DNA can a regulator bind to in order to halt transcription?
What is the main reason for prokaryotes to transcribe only the genes that their end-proteins are needed at the time?
In an operon, which DNA-binding protein inhibits the expression of genes by binding to the operator?
What distinguishes inducible operons from repressible operons?
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In Rho-dependent transcription termination in prokaryotes, what role does the Rho factor play?
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What is the key sequence feature that triggers Rho-independent transcription termination in prokaryotes?
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What is the function of the Shine-Dalgarno sequence in prokaryotic translation initiation?
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What is the primary role of the 30S ribosomal subunit during translation initiation in prokaryotes?
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What happens when the RNA polymerase reaches a terminator sequence during Rho-independent transcription termination?
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What is the final step of translation initiation in prokaryotes before the initiation complex is fully formed?
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What is the function of lacZ in the lac operon?
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Why do repressible enzymes suspend production when the end product is in high enough concentration?
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Which statement about tryptophan synthesis in E. coli is correct?
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What happens to the lac operon when lactose is present?
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Which enzyme transports lactose into the cell in the lac operon?
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What is the role of corepressors in regulating gene expression?
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Why do inducible enzymes break down a particular nutrient only when it's available?
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Which operon can be turned off by a small molecule acting as a corepressor?
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What is the function of RNA polymerase in transcription initiation?
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Study Notes
Transcription Regulation
- A regulator binds to an operator segment of DNA to halt transcription.
- Prokaryotes transcribe only the necessary genes at a given time because they lack a nucleus and cannot store transcripts, making it more efficient to transcribe only what's needed.
Operon Regulation
- A repressor protein binds to the operator to inhibit gene expression in an operon.
- Inducible operons are activated when a specific molecule (inducer) is present, whereas repressible operons are inhibited when a specific molecule (corepressor) is present.
Transcription Termination
- Rho-dependent transcription termination: Rho factor plays a role in unwinding the RNA-DNA hybrid, terminating transcription.
- Rho-independent transcription termination: a terminator sequence (GC-rich region followed by a poly-U tract) triggers termination.
Translation Initiation
- The Shine-Dalgarno sequence is a recognition site for the 30S ribosomal subunit to bind and initiate translation.
- The 30S ribosomal subunit plays a key role in recognizing the initiation site and binding to the mRNA.
Transcription Termination and Initiation
- When RNA polymerase reaches a terminator sequence, it releases the transcript and dissociates from the DNA.
- The final step of translation initiation is the formation of the initiation complex, which is fully formed when fMet-tRNA binds to the 30S ribosomal subunit.
lac Operon
- The lacZ gene codes for β-galactosidase, an enzyme that breaks down lactose.
- Repressible enzymes suspend production when the end product is in high concentration to prevent wasted energy.
- In the lac operon, the presence of lactose triggers the transcription of genes necessary for lactose breakdown.
- The enzyme β-galactosidase permease transports lactose into the cell.
Gene Regulation
- Corepressors inhibit gene expression by binding to a repressor protein, which then binds to the operator.
- Inducible enzymes break down a particular nutrient only when it's available to conserve energy.
- The tryptophan operon can be turned off by a small molecule acting as a corepressor.
Transcription Initiation
- RNA polymerase plays a key role in initiating transcription by binding to the promoter region and unwinding the DNA double helix.
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Description
Test your knowledge on how gene expression occurs in prokaryotes, focusing on transcription, operons, and the regulation of gene expression based on the immediate environment. Understand how prokaryotes efficiently transcribe genes as needed to conserve energy.
