bacterial gene structures Flashcards
What is the genetic composition of bacteria?
Bacteria are haploid, with one circular chromosome. Accessory genes may be on plasmids.
Why do bacteria regulate gene expression?
To adapt to environmental changes by switching on necessary genes and switching off unneeded ones, preventing functional interference.
What are the three essential features of bacterial genes?
Promoter: Contains sequences for expression and regulation (not part of mRNA).
Transcribed Region: Includes one or more ORFs; part of mRNA.
Terminator: Defines the end of the gene or operon (often a stem-loop structure).
What are the components of bacterial mRNA?
5’ Untranslated Region (UTR) before the start codon (AUG).
Translated Region containing ORFs.
3’ UTR with terminator for stability.
What is the role of RNA polymerase in bacteria?
Synthesizes mRNA by binding the promoter (-10 and -35 motifs).
Core enzyme + Sigma factor = Holoenzyme.
Starts transcription at the +1 site and ends at the terminator.
What are the two modes of transcription termination in bacteria?
Intrinsic (Rho-independent): RNA pol slows down at a stem-loop structure and polyA sequence.
Rho-dependent: Rho protein acts as a molecular motor to separate RNA from RNA pol.
How does bacterial translation begin?
Ribosome binds to the Ribosome Binding Site (RBS) and starts at the AUG codon (methionine).
What is an operon?
A set of related genes regulated by a single promoter, producing polycistronic mRNA with multiple ORFs.
What is meant by polar mutations in bacterial genes?
Mutations in the first gene of an operon can introduce an early terminator, affecting downstream gene expression.
What is coupled transcription and translation?
In bacteria, transcription and translation occur simultaneously in the cytoplasm, with translation often beginning before transcription ends.
What is the difference between positive and negative regulation in bacteria?
Negative Regulation: Repressor proteins block RNA polymerase (e.g., LacI). Inducers relieve repression.
Positive Regulation: Activators help RNA polymerase bind to weak promoter motifs.
What are the learning outcomes for bacterial gene regulation?
Identify elements of the promoter (-10, -35 motifs).
Describe operon structure and polycistronic mRNA.
Explain coupled transcription and translation.
Understand positive and negative gene regulation.
