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
- 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.
