Lecture 5 Flashcards
Operon
A cluster of 2 or more genes that share an upstream control (regulatory) region and a termination sequence. Co-transcribe genes.
Trip Operon
Response to Environmental stimuli
E. coli can synthesize most molecules needed for growth
Repressible Operon
Something is added or accumulates (Trp) that turns off transcription
Inducible genes
Genes get “turned on” or activated when conditions change
Example:
E. coli prefers glucose but in glucose-free conditions, it can metabolize lactose
-but first, it needs to make genes that can metabolize lactose
Inducible Operon—Lac Operon
Default is off
-When lactose is added, it binds to repressor and pushes it off allow transcription to occur
Catabolism repression
Catabolite activator protein (CAP)
Two mechanisms:
-Lactose present, but no glucose
-Lactose present+glucose present
Inducible promoter
-E. coli prefers glucose
-when glucose is gone:
•lactose inactivates the repressor
•cAMP increases to activate transcription
Operon vs regulon
Regulon—when more than one Operon is under control of the same regulatory protein, the Operon are referred to as regulons
-Stress response
-Pathogenesis
-Phosphate deprivation
-Presence of maltose
Translation
Protein synthesis
sRNA
Small RNA
Mutation
Change in the DNA base sequence (nucleotides) of genome
Spontaneous mutation
Errors in DNA replication
Missense mutation
Change in amino acid
Nonsense mutation
Stop codon
Silent mutation
No amino acid change (wobble)
Frameshift mutation
Insertion or deletion of one or more nucleotide pairs
Spontaneous mutation rate
1 error every 10^9 replicated base pairs=1 error in every 10^6 replicated genes
Mutagens
Increase to 1 error in every 10^3 replicated gene
Chemical mutagen examples
-Nitrous acid (HNO2)
-Nitrosamine (HN2O2)
Physical mutagen examples
-UV light
•absorbed by DNA
-ionizing radiation
•causes breaks in DNA
•for cancer treatment + nuclear bombs
•nasty radiation
Clastogens
-Lead to Genomic instability
Examples:
Acridine yellow, arsenic, benzene
Three types of DNA repair
- SOS repair
- Photolyases
- Nucleotide excision repair
SOS repair
Initiates regulon activity where over 40 genes are involved in different types of repair, growth arrest, & apoptosis.
Photolyases
Separate thymine dimers
