Lecture 3 - Regulation of Gene Expression in Prokaryotes Flashcards
What is the central dogma of molecular biology?
DNA is transcribed into RNA, and RNA is translated into proteins.
What are structural RNAs, and how do they differ from mRNAs?
Structural RNAs (e.g., tRNAs, rRNAs) are not translated into proteins but play functional roles in cellular processes.
How are transcription and translation coupled in prokaryotes?
In prokaryotes, ribosomes begin translating mRNA while it is still being transcribed because there is no nuclear membrane.
What are the key regions of a gene in transcription?
Promoter: Upstream region where RNA polymerase binds.
Terminator: Downstream region signalling RNA polymerase to stop transcription.
5’ UTR: Contains the ribosome binding site.
What is an operon?
An operon is a cluster of genes transcribed together from a single promoter, producing polycistronic mRNA.
What is the role of sigma factors in prokaryotic transcription?
Sigma factors guide RNA polymerase to specific promoters and determine which genes are transcribed.
How is transcription terminated in prokaryotes?
Transcription ends when a hairpin structure followed by a stretch of uracils destabilizes the RNA-DNA hybrid, causing dissociation.
Why do cells need different amounts of proteins?
Different proteins have specific roles and are required in varying quantities depending on cellular needs.
How do strong and weak promoters affect transcription?
Strong promoters: RNA polymerase binds frequently, leading to high transcription.
Weak promoters: RNA polymerase binds less often, resulting in lower transcription.
How can promoter strength be tested?
By fusing promoters to reporter genes like GFP or lacZ and measuring fluorescence or enzymatic activity.
What are the four levels at which gene expression can be regulated?
Transcription, post-transcription, translation, and post-translation.
What is the role of alternative sigma factors?
Alternative sigma factors enable RNA polymerase to recognize and transcribe specific sets of genes in response to environmental changes.
What is a regulon?
A group of genes scattered across the genome that are co-regulated by the same sigma factor.
How does negative regulation work in gene expression?
A repressor binds to the operator, blocking RNA polymerase from binding to the promoter, turning transcription off.
How does positive regulation work in gene expression?
An activator binds near the promoter, helping RNA polymerase bind and initiate transcription.
What is the lac operon?
A transcriptional unit in bacteria that contains genes (lacZ, lacY, lacA) needed for lactose metabolism.
How does the lac repressor (LacI) regulate the lac operon?
LacI binds to the operator in the absence of lactose, preventing transcription.
What is the role of CAP and cAMP in positive regulation of the lac operon?
cAMP binds to CAP, enabling it to bind near the promoter and enhance RNA polymerase binding when glucose is absent.
What is allosteric regulation?
A regulatory molecule binds to a site other than the active site, causing a conformational change that affects protein function.
What is the role of allolactose in the lac operon?
Allolactose binds to LacI, causing it to release from the operator and allowing transcription.
What causes lactose intolerance?
Reduced expression of the LCT gene after infancy due to regulatory elements in the MCM6 gene.
How do bacteria prioritize glucose over lactose for metabolism?
Glucose inhibits cAMP production, preventing CAP activation and reducing lac operon transcription.
What is a partial diploid in bacteria?
A bacterial cell with two copies of certain genes, one on the chromosome and one on a plasmid.
What are bacterial plasmids, and why are they important?
Plasmids are circular DNA molecules that carry genes for antibiotic resistance, toxin production, or metabolic functions.
How is transcription different in prokaryotes and eukaryotes?
In prokaryotes, transcription and translation are coupled, while in eukaryotes, transcription occurs in the nucleus and translation in the cytoplasm.
How is lactose commercially produced?
Using fungi like Kluyveromyces lactis or Aspergillus niger to enzymatically convert lactose into glucose and galactose.
How can lactose production be increased in bacteria?
Mutate the CAP gene to no longer require cAMP and delete the LacI gene to remove repression.
What is the significance of -10 (TATA box) and -35 sequences in promoters?
These sequences are recognized by sigma factors to initiate transcription.
What is the relationship between glucose, cAMP, and CAP?
High glucose inhibits cAMP production, which prevents CAP from activating transcription.
Why do cells regulate gene expression?
To conserve energy and resources by producing only the proteins needed for current conditions.
