S.Nance: Gene Organization & Expression Flashcards
Chromosome
Chromosome – single circular, very little non-coding DNA
Exceptions for chromosome
two circular – vibrio, linear – Borrelia
Chromosome Function
Function – code for normal growth products
Plasmids
Plasmids – extrachromosomal DNA, covalently closed rings, some linear
Plasmid function
Function – non-essential for normal growth, antibiotic resistance and virulence genes, promote their own transfer (conjugative)
Horizontal gene transfer
Horizontal gene transfer – acquiring DNA from the environment and incorporating into bacterial genome (not from mother cell)
Pathogenicity islands
Pathogenicity islands – Type 3/4 secretion systems, MRSA, β lactam resistance
Genetic Replication of Chromosome
Chromosome – single origin (oriC) → DnaA recognizes oriC → bidirectional replication → forks meet on the opposite side
Genetic Replication of Plasmids
Plasmids – encode oriV → Rep to recognize oriV → replication, oriT → transfer to another cell
Gene Transcription: Operons
Operons – genes in the same metabolic pathways, induced or repressed when needed
Gene Transcription: RNA polymerase
RNA polymerase – single enzyme for transcription, reads until it reaches promoter sequence – terminator of hairpin repeats
Gene Transcription: Positive Control
Positive control – activate transcription, ex: cAMP inversely relates to glucose content
Gene Transcription: Negative Control
Negative control – block transcription, prevent RNA polymerase binding/leaving promoter region
Two component systems:
Two component systems: sensing environment signals
Sensor Kinase Component
Sensor kinase – auto-phosphorylates in response to signal → phosphorylates response regulator → regulates gene transcription, Ex: Salmonella in low Mg2+
Quorum Sensing Component
Quorum sensing - senses the number of bacteria in the area, higher signal/peptide with more bacteria → crosses threshold → alters behavior/expression/toxin release/biofilm
(+) Glucose & (-) Lactose
no cAMP
Lac repressor active
Lac operon repressed
(+) Glucose & (+) Lactose
no cAMP
Lac repressor inactive
Lac operon weakly expressed (10%)
(-) Glucose (+) Lactose
cAMP present
Lac Repressor Inactive
Lac Operon maximally expressed
(-) Glucose & (-) Lactose
high cAMP
Lac Repressor Active
Lac Operon Repressed
What is the preferred metabolic substrate of E. Coli?
Glucose
When glucose is absent and lactose is available, the lac operon is
activated to switch to lactose metabolism
Lac operon is a classic example of a genetic response to
environmental change
