Regulation of gene expression in prokaryotes and eukaryotes Flashcards
Compare the transcriptional and translational processes in prokaryotes and eukaryotes • Examine the mechanisms of RNA processing • Relate the effects of post- translational modifications to protein structure and function (20 cards)
- What is the primary level at which prokaryotic gene expression is regulated?
Transcription initiation is the primary level of regulation. It determines whether RNA polymerase can bind to the promoter and start transcription.
- What is an operon, and what are its components?
An operon is a group of functionally related genes that are regulated together and transcribed as a single mRNA. Its components include a promoter, operator, and structural genes.
- What is the difference between inducible and repressible operons?
Inducible operons (like lac) are normally off and turned on in the presence of an inducer. Repressible operons (like trp) are normally on and turned off when a corepressor is present.
- How does the lac operon respond to the presence of lactose?
Lactose (via allolactose) inactivates the lac repressor, allowing RNA polymerase to transcribe the operon’s genes for lactose metabolism.
- What role does cAMP play in the regulation of the lac operon?
cAMP binds to CAP, and this complex enhances transcription by helping RNA polymerase bind to the promoter. It’s active when glucose levels are low.
- What happens to the trp operon when tryptophan is abundant?
Tryptophan acts as a corepressor, binding to the trp repressor and enabling it to attach to the operator, blocking transcription.
- What is attenuation and how does it regulate the trp operon?
Attenuation is a form of premature transcription termination. When tryptophan is abundant, a terminator structure forms in the mRNA leader sequence, halting transcription before the structural genes are transcribed.
- What is the function of the AraC protein in the arabinose operon?
AraC can act as both a repressor and an activator. In the absence of arabinose, AraC represses transcription. When arabinose is present, AraC changes shape and activates transcription.
- What is a constitutively expressed gene?
A gene that is constantly expressed at a fixed rate, regardless of environmental conditions, because its product is always needed.
- How do repressor proteins control gene expression in prokaryotes?
Repressors bind to operator sequences in operons to block RNA polymerase from transcribing genes. This prevents the unnecessary production of proteins.
Compare and contrast the regulation of gene expression in prokaryotes and eukaryotes.
Prokaryotic gene regulation primarily occurs at the transcriptional level and often uses operons like the lac and trp operons to turn gene expression on or off depending on environmental conditions
. In contrast, eukaryotic regulation is more complex, involving transcriptional, post-transcriptional, translational, and post-translational control. Eukaryotes also have chromatin remodeling to manage DNA accessibility, and default gene expression is often “off” until activators initiate transcription
What molecular tools are used to study genes and gene activity?
Researchers use reporter genes (like lacZ), DNA microarrays, and RNA sequencing to study gene expression. Additionally, mutational analysis and the use of inhibitors (like actinomycin D and rifampicin) help identify the roles of specific genes and proteins in transcription
How do protein-DNA interactions influence gene regulation?
Protein-DNA interactions are crucial for regulating gene expression. Proteins such as repressors and activators bind to specific DNA sequences like operators or enhancers to inhibit or promote transcription, respectively
. For instance, the lac repressor binds to the lac operator to block RNA polymerase
Describe the major DNA-binding motifs found in transcription factors.
The four major DNA-binding motifs are the zinc finger, helix-turn-helix, leucine zipper, and helix-loop-helix
. These motifs allow transcription factors to bind specifically to DNA, facilitating gene activation or repression.
Explain the regulatory mechanism of the lac operon.
The lac operon is an inducible system where the presence of lactose leads to inactivation of the lac repressor, allowing transcription of genes needed for lactose metabolism
. Additionally, the absence of glucose increases cAMP, which binds to CAP and enhances RNA polymerase recruitment for strong gene expression
.
What are transcription activators and how do they function
Transcription activators are proteins that bind to enhancers and help recruit the transcriptional machinery to the promoter
. In eukaryotes, activators often recruit co-activators and chromatin remodelers to open up DNA and enhance transcription
.
Define RNA interference (RNAi) and its biological significance.
RNA interference (RNAi) is a mechanism where small RNAs (siRNAs and miRNAs) guide the degradation or translational repression of target mRNAs
. It plays a vital role in regulating gene expression, defending against viruses, and maintaining genome stability.
Distinguish between miRNAs and siRNAs.
miRNAs are endogenous non-coding RNAs that typically repress translation or promote degradation of target mRNAs imperfectly
. siRNAs, often exogenous, induce perfect cleavage of target mRNAs. Both involve the RNA-induced silencing complex (RISC)
How is translation control achieved in eukaryotes?
Translation control occurs through regulation of initiation factors, mRNA stability, and RNA-binding proteins
. For example, ferritin mRNA translation is controlled via an iron-response element (IRE) that blocks or permits translation depending on iron levels
What role does chromatin structure and remodeling play in gene expression?
Chromatin structure determines DNA accessibility. Active genes are associated with open euchromatin, while silent genes are packed in heterochromatin
. Chromatin remodelers like SWI/SNF and histone modifiers such as HATs (acetylation) and HDACs (deacetylation) adjust chromatin to either facilitate or inhibit transcription
