Lecture 5 Flashcards
What dose genetically stable mean
That there is no errors in the DNA
What is DNA damage
It is any alteration to DNA that distorts its geometry
What are the 2 characteristics of DNA damage
Single stranded damage (SSD)
Double stranded damage (DSD)
What is SSD
It’s damage on one of the 2 DNA strands and is caused by endogenous replication errors alkylating/oxidative chemicals Nonionising radiation eg UY rays
What is DSD
It’s damage on both strands due to anti tumour agents such as Cisplatin, ionising radiation eg gamma rays
Damage caused by replication errors is fixed by
Mismatch repair
What is damage cause by uv light fixed by
NER
What is damage caused by X-rays fixed by
Recombinational repair
What are the types of SSD
Base mismatch
Depurination
Deamination
Thymine dimers
Bulky adducts
What is base mismatch
Distorted geometry of DNA (associated with errors in DNA replication)
What is depurination
Reaction resulting in removal of purines A or G from sugar and phosphate
What is deamination
Loss of an amino group from cytosine to produce uracil or adenine to produce hypoxanthine=change of base chemical properties
What is thymine dimers
Covalent linkage of 2 adjacent thymines together (associated with UV radiation)
What is bulky adducts
That occur from DNA intercalating agents eg ethidium bromide or anticancer agents eg cisplatin binds to bases and forms bulky lesions in DNA helix
What is base mismatch a result from
Endogenous replication error
What are depurination and deamination a result from
Endogenous spontaneous errors from metabolic processes
What is the difference between damage and mutation
DNA damage is often defined as a mutation but this is only when randomly produced permanent in a sequence of DNA is caused
What happens when a mutation affects a single nts pair
It can severely compromise an organisms fitness if the change occurs in a vital position in the defective protein
If a mutation occurs in the coding DNA
It can result in a defective protein
Example of mutation
Sickle cell anaemia
3 DNA repair processes for single strand damage
Mismatch repair (MMR)
Base pairs excision repair (BER)
Nucleotide excision repair (NER)
What is mismatch repair
It’s for repairing rare mistakes made during DNA replication process that escape DNA polymerase III and I proofreading error rate 1 in 10p9 nts
What is BER
It’s for repairing modified DNA bases from depurination or deamination
What is NER
It’s for repairing bulky lesions and distortion in DNA
What happens if the mismatch is left
It will result in a permanent mutation in the next round of DNA replication
