Lecture 2 - regulation of microbial gene expression Flashcards
(20 cards)
what happens in gene expression in prokaryotes?
RNA polymerase binds to promoter
Sigma factor binds to RNA polymerase and guides it to promoter
Following transcription initiation, Sigma factor will dissociate and transcription will continue
what is an operon?
A cluster of functional co-regulated genes
Adjacent genes on the same chromosome
A set of genes regulated together, controlled by a single promoter
what is the Importance of mRNA structure in transcription and translation?
Prokaryotes have no introns, eukaryotes do (mostly)
Eukaryotic mRNA has 5’ cap and 3’ poly A-tail to protect transcript when moving from nucleus to cytoplasm from degradation
Prokaryotic mRNA does not, as transcription and translation are coupled, and both occur in cytoplasm
what is the genomic structure and transcription?
Bacteria often have genes clustered together-operon
These genes are transcribed all at once as a single mRNA
Termed ‘polycistronic mRNA’
Promoter-binding of RNA polymerase
Operator-binds transcription factors
-responds to changes in environment allowing for alterations in synthesis of proteins, conserving energy
what is the e.colis genome structure?
Housekeeping genes
-constitutively expressed
-example-metabolism-catabolic process
Inducible genes
-Certain genes not required all the time
-example-biosynthesis of amino acids
Enzymes are synthesized only when they are needed no wasted energy
how do you control the lactose operon?
Inducible genes -
three structural genes coding for lactose uptake and metabolism
Lactose is broken down into glucose and galactose
lac repressor (lacI) binds operator
inhibits transcription
Enzymes normally not produced unless lactose present
In the lac operon of E. coli, which of the following scenarios would result in the highest level of transcription of the lac operon genes?
Low levels of glucose and high levels of lactose.
Lac operon only operates when lactose available, binds repressor, blocking binding to operator, allowing transcription.
The trp operon in E. coli is involved in the synthesis of tryptophan. Which of the following statements about the trp operon is correct?
The trp operon is repressed when tryptophan levels are high.
Tryptophan binds to repressor molecule that binds to operator, blocking translation
how is Transcription And Translation In Prokaryotes are coupled?
mRNA is transcribed as one long molecule, then ribosomal subunits bind, synthesising proteins
what is the lac operon?
NO LATCOSE
lac repressor binds to operator, blocking transcription
LACTOSE
Lactose binds to lac repressor, allowing RNA polymerase to transcribe 3 lac genes
Negative control mechanism
-repression
how do you Control of the trp operon?
Tryptophan metabolism: biosynthesis of the amino acid tryptophan if not available in environment
Low levels of trp present-new trp synthesised
High levels of trp present-no trp synthesised
Trp repressor binds to trp, blocking transcription of operon
what is the The Tryptophan (trp) Operon?
Consists of 5 structural genes which code for enzymes needed to synthesize tryptophan
Transcriptional control of repressible genes by trp repressor
Operon only functions in the absence of tryptophan
what is Attenuation-trp operon?
Blocks transcription of mRNA transcript, not initiation
Occurs when levels of tryptophan high
RNA polymerase stops prematurely during transcription due to structural changes in secondary structure
Shortened mRNA does not function
what is the New research in the field/application?
Regulators well studied in E.coli, not pathogenic bacteria
New research from Dr Gill Douce on uropathogenic E.coli (urinary tract & bloodstream infections)
Regulates pathogenic ability using a transcriptional regulator YhaJ that coordinates tryptophan biosynthesis and fimbrial adhesion
Could be used to design inhibitors of biosynthetic pathways
what are the Transcriptomics-monitoring gene expression differences?
Transcriptome: All RNA molecules in a cell, or a population of cells
Transcriptome analysis methods
Examples: mRNA levels of genes during life cycle or growth stages, effects of a mutation on other genes
Often work with cDNA=complementary DNA
Use Reverse transcriptase to make DNA from RNA→cDNA
Useful for PCR, as can only use DNA as a template
RNA-Sequencing Methods-different methods now available
Next generation sequencing technology-whole transcriptome information
what are Molecular mechanisms of human infectivity of African trypanosomes?
African sleeping sickness →Trypanosoma brucei
what is the Human infectivity of African trypanosomes?
T.b.gambiense: causes a chronic disease that can take years to develop. 98 % of cases
T.b.rhodesiense: causes an acute disease that can be fatal in a matter of months if not treated. 2 % of cases
Fatal if not treated
No vaccine
what is Polycistronic transcription & translation?
Ribosomal binding sites in between each gene
5’ and 3’ UTRs at either end of each gene transcribed
what is lac operon-a second, positive control mechanism -activation?
Also regulated by catabolite activator protein (CAP)
Binds to CAP site, driving transcription
Regulates in response to presence or absence of glucose
Low glucose-CAP activates transcription (of many operons)
cAMP produced in response to no glucose, binds to CAP, in turn activates RNA polymerase and initiates transcription
what is T.b.brucei?
Cannot survive in human serum due to ApoL-1 killing parasite
