Week 6 microbiology

Where does transcription and translation occur in prokaryotes?

-occurs in the same compartment -translation can begin before transcription is complete and multiple ribosomes can translate the same mRNA strand

What are open reading frames (ORFs)?

-between START and STOP codons -nucleotides are 'read' in groups of three (codon) -functional ORF are translated to functional proteins -microbial DNA are a series of ORFs

What is initiation of transcription?

-fewer elements than eukaryotes -RNA polymerase binds to promoter region located -35 to -10 upstream -the sense strand is the same sequence as the transcribed mRNA

What is polycistronic mRNA?

in bacteria genes from related functions are often clustered and transcribed together

What are gene clustered organised in?

operons

What does an operon include?

a promoter, an operator and a cluster of genes

What is the initiation of translation?

the 50S subunit then binds and begins translation at the first start codon AUG

Why does bacteria need to regulate which genes are on and off?

-some genes are expressed all the time, others are switched on and off as needed -this allows bacteria to rapidly respond to their environment -phase variation -transcriptional variation -translational variation

What are the steps to phase variation?

1. site specific inversion 2. slipped strand mispairing

What is site specific inversion?

a recombinant event that flips the orientation of a gene or segment of DNA

What is slipped strand mispairing?

-short repeats displace DNA, this occurs during DNA synthesis (replication or repair) -frameshift mutation

What are the two mechanisms that regulate transcription?

-repression: turn off gene expression -induction: turns on gene expression

What are transcription factors?

-activator proteins and repressor proteins -activator proteins bind to promoter -repressor proteins bind to the operator

What happens when effector molecules bind to transcription factors?

changes its shapes to either allow binding to DNA or inhibit binding (allosteric change)

How is Lac operon expression regulated?

-by an activator (CAP - catabolite activator protein) -the activator must be bound to the promoter for transcription to occur

What is regulatory RNA?

small RNAs (sRNAs) are able to base pair directly to other RNAs to modulate translation

What are riboswitches?

segment in mRNA that resembles repressors or activators to control expression of genes

How does bacteria respond to their environment?

-bacteria sense their environments by detecting molecules either internally or on their surface -nutrient availability -pH -temperature -oxygen

How does bacteria adapt to a changing environment?

-changing their metabolism -changing direction of movement

What is signal transduction?

a signal will be detected on the bacterial cell surface and needs to be relayed internally to the regulatory protein

What is the process of signal transduction?

1. sensor kinase 2. response regulator 3. feedback loop

What is sensor kinase (integral protein)?

detects stimulus and autophosphorylates

What is response regulator (cytoplasmic protein)?

phosphate is transferred to the regulator which then alters gene expression

What is feedback loop?

removes phosphate at a constant rate so cycle can start again

How is Chemotaxis achieved?

-achieved with a modified two-component regulatory system -attracted to a molecule (e.g. a nutrient) -repelled by a molecule (e.g. a harmful substance)

What does chemotaxis do?

-alters action of an existing protein rather than transcription 1. response to signal 2. regulation of flagella rotation 3. feedback loop

What is quorum sensing?

-communication amongst bacteria, which allow them to coordinate gene expression -density-dependent -biofilm development -virulence factors

How does quorum sensing work?

-cells produce autoinducers that can freely cross the cell envelope (the more cells present, the stronger the signal) -autoinducers can bind to a transcriptional activator proteins or sensor kinase

What do quorum sensing and biofilms do?

regulates metabolism, virulence factors, matrix development and dispersal