endogenous sources of DNA damage - ANSWERSHydrolysis, oxidation, methylation
Hydrolysis - ANSWERSabout 10,000 damages
Oxidation - ANSWERSabout 3,000 damages
reactive oxygen species from the body's cells (free radicals)
Methylation - ANSWERSabout 4,000 damages
How do damaged bases cause mutation? - ANSWERSBy changing base pairing properties and causing
incorportation of a wrong base during the next round of DNA replication
External sources of DNA damage - ANSWERSRadiation (IR and UV)
Passive mechanims to protect the DNA against oxidative damage - ANSWERSCompartmentalization
(reduced ROS in the nucleus)
Chromatin packaging (ROS protein "bumper")
Spurs and Blobs - ANSWERSRadiation interactions create multiple local ionization events and can attack
multiple bonds in the DNA in a single hit
Radiation and Compartmentalization - ANSWERSRadiation defeats compartmentalization by creating free
radicals inside the nucleus next to DNA
, Largest class of endogenous damage - ANSWERSDNA replication errors and ribonucleotide incorporation
DNA replication fidelity is determined by: - ANSWERSDNA polymerase proofreading activity and DNA
mismatch repair
Double strand breaks - ANSWERSCritical lesions
Potentially lethal
Lead to chromosomal rearrangements
Major sources of recombinogenic structures - ANSWERSDouble strand breaks
Sources of double strand breaks - ANSWERS- collapsed replication forks when single stand break is
present in template strand
- stalling and collapsing of replication fork when damaged base is present in the template strand
- radiation
Methods for detecting DSBs - ANSWERS- Pulse Field Gel Electrophoresis
- Comet Assay
- Immunofluoreresce microscopy detection of foci of DNA damage response enzymes
Pulse Field Gel Electrophoresis - ANSWERSseparate molecules up to 6 megabases, fragmented human
chromosomes or whole yeast chromosomes
Non-homogous end joining - ANSWERSPrevalent repair pathway in mammalian cells
NHEJ pitfalls - ANSWERSmay not join the corrent pair of DNA ends when multiple DSBs are present
Homologous recombination - ANSWERSuses an intact identical DNA molecule as template to repair DSBs
accuratley
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