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DNA Mutations and Genetic Repair Complete Summary
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Fully indepth summary of the DNA mutations and genetic repair section of MCB2023S
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DNA Mutations, Damage and RepairLECTURE 1
• Mutations = inherited change in genetic information
• DNA is susceptible to change
o Weak molecule
o Driving force in evolution
o But too much change is lethal
GENETIC VARIATION IN BACTERIA
• Much easier to study than eukaryotes
• Rapid growth
o 1-109 in 12 hrs
• Approx 1/109 = spontaneous mutation
• Haploid genome à easy to spot changes
• External agents can increase mutation rate
CONSEQUENCES OF MUTATIONS
• General value
o Bad
§ Antibiotic resistance
§ Pathogenicity
o Good
§ Industrial processes/biotech
§ Evolution
• Scientific value
o Useful tools
§ Gene regulation
§ Assign function to genes
§ Understand biological processes
Genotype = genetic information on the genome
Phenotype = physical characteristics in that environment (genotype + environment)
Wild type = not altered with respect to the particular geno/phenotype being
Examined
CAUSES OF MUTATIONS
• Induced mutations
o Radiation
§ UV
§ X rays
o Chemicals
, § Nicotine
§ Nitrate and nitrate preservatives
§ Benzoylperoxide
o Infectious agents
§ HPV
HOW DO INDUCED MUTATIONS OCCUR
• Induced errors
o External factors
§ Contact with damaging agent (mutagen) in the environment
• Chemical
• Physical
• Infectious agent
Mutagen directly damages DNA, alters its chemistry or interferes with its functioning
MUTAGEN & GENOTOXICITY
• Mutagen = substance or agent that induces heritable changes in cells or
organisms
o Raises the frequency of mutation above the spontaneous rate
• Carcinogen = mutagen that induces unregulated growth processes in cells or
tissues of multicellular animals leading to cancer (tumour)
o Carcinogenesis = result of mutagenic events
• Genotoxicity = property of chemical agents to cause damage to genetic
information within a cell causing mutations which are not necessarily
heritable
ALL MUTAGENS = GENOTOXIC BUT NOT ALL GENOTOXIC SUBSTANCES =
MUTAGENIC
SPONTANEOUS MUTATION OCCURANCE
• Spontaneous errors
o Natural errors – normal cell processes
§ Metabolism
• By products of metabolism
o Free radicals
o ROS = reactive oxygen species
§ DNA replication errors
• Incorrect proof reading by DNA pol
§ Mobile genetic elements
, MUTANT TYPES
1. Auxotrophic mutants
a. Identify bacteria unable to grow under certain nutrient conditions
i. Need particular growth element to be supplied in order to grow
1. Eg. Amino acids
ii. Cannot use particular carbon source
1. Select on MacConkey agar medium + Carbon source (eg
lactose)
2. Drug resistant/sensitive mutants
a. Direct selection on nutrient agar + drug
3. Conditional lethal mutations
a. Gene product not entirely inactive, mutations in the gene
b. Functions at permissive temp and non functional at others
c. Used for studying regulatory genes
d. Temperature sensitive mutants (Ts)
i. Bacteria cannot grow at high temps
e. Cold sensitive mutants (Cs)
i. Bacteria can form colonies at low temps
BACTERIAL GENOTYPE NOMENCLATURE
E. coli BL21(DE3) pLysS
– – – +
F ompT gal dcm lon hsdS (r m ) λ(DE3 [lacI lacUV5-T7p07 ind1 sam7 nin5]) [malB ]
B B B K-
S R
(λ ) pLysS[T7p20 ori ](Cm )
12 p15A
• Gal à strain cannot use galactose
• Deficient in OmpT and Lon proteases
• λ = phage
• pLysS = plasmid resistant to chloramphenicol
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