Cellular response to DNA Damage and Repair Flashcards
What type of DNA damage does Base Excision Repair take care of?
DBSC; Depurination, Base Oxidation, Single-stranded break, or cytosine deamination.
How are double stranded breaks repaired?
Double Stranded Break Repair. or non-homologous end joining.
Thymine Dimers
UV light introduces thymine dimers (Fixed by nucleotide excision repair)
What type of DNA damage does Nucleotide Excision Repair take care of
Thymine Dimers and Bulky Adducts.
Base Mismatch
wrong base is attached to each other (Fixed by Mismatch repair)
How is base alkylation repaired?
Direct Reversal.
How do point mutations occur?
Mispairing; insertion of base analogs, or chemical mutagens (Nitrous acid, hydroxylamine and alkylating agents)
How do DNA mutations occur (3)
1) Mistakes during DNA replication 2) DNA subject to spontaneous damage (Deamination or Depurination) 3) Induced damage can lead to mutations caused by environmental agents (Chemical mutagens, UV radiation)
Oxidative Deamination
1 ) C to U (Now pairs with A) 2) A to hypoxanthine (now pairs with C) 3) G to Xanthine ( still pairs with C) 4) 5-methylcytosine to Thymine.
8-Oxoguanine
Produced when guanine is oxidized; base pairs with Adenine now.
Alkylation
Methylation; Guanine goes to O5-methyl guanine; binds with T, when guanine should bind with C
Oxygen Radical Damage
Breaks sugar rings
Spontaneous Base Loss
Glycosyl bond linking DNA bases with deoxyriboes is labile under physiological condition. Loss of a purine or pyrimidine base creates an apurinic or apyrimidic site. Happens through hydrolysis.
Nitrous acid
HNO2 Causes Oxidative deamination
Intercalating agents
Ethidium bromide, acridine orange) distort the helic causing frameshift mutations.
