DNA Damage And Repair Flashcards
What happens if DNA is not repaired before the next replication cycle
The error becomes permanent and forms a mutation
What happens to damaged DNA in germ cells if it is not repaired
The lesion will be transmitted to the offspring
Where does DNA damage come from
Errors of DNA replication: despite its proofreading capabilities, DNA polymerase still has an error rate of 10^-10
Mutagens: chemical and environmental agents that cause changes in DNA molecules
What is a tautomere
Isomers with slightly different chemical structures
What are the different types of DNA damage
Single base alterations
Two base alterations
Chain breaks
Cross linkages
What are some deaminating agents and how do they effect DNA
Nitrous acid or sodium bisulphate
Deaminating base pairs like adenine will form hypoxanthine
Hypoxanthine pairs with C instead of T
What does the deamination of cytosine cause
Uracil
Binds with A instead of G
What does the deamination of guanine do
Forms xanthine
Blocks DNA replication
How does UV light cause DNA damage
It causes thymines to bind together (thymine dimerisation)
What is an intercalating agent
A chemical agent that inserts itself between base pairs
Ethidium bromide
What arc the different categories of mutations
Chromosomal mutations
Base pair mutations
What are the different types of chromosomal mutations
Duplication
Inversion
Deletions
Insertion
Translocations
What are the different base pair mutations
Insertion
Deletion substitution
What is a base pair transition
When a purine mutates into another purine (A to G) / pyrimidine into another pyrimidine (T to C)
What is a base pair transversion
When a purine mutates into a pyrimidine or vice versa (A to T or G to C)
Why are point mutations dangerous
If the mutation forms a premature stop codon the protein will be truncated and likely stop functioning
What are the different effects of point mutations
Silent: mutation has no effect since degenerate code means the same amino acid is generated
Missense: mutation cause a single amino acid to change in a sequence
Nonsense: mutation causes a premature stop codon to form
Frameshift mutation: insertion/deletion causes a shift in the reading frame likely altering a large portion of the peptide chain
What are the different pathways of DNA repair
Direct repair
Repair by excision
Mismatch repair
What happens during direct damage reversal (DDR) of DNA
An enzyme corrects a nucleotide alteration caused by mutagens
What happens during the mismatch repair of DNA
DNA is corrected during DNA replication
Parent strand has the correct nucleotide, daughter strand contains mutation
The parent strand is distinguished from the daughter strand through hemimethylation (only the parent strand is methylated
MutS, MusL, MutH mediated the process
MutS bind to the mutation, MusL follows and MutH cuts out a large portion of DNA including the mismatch
DNA polymerase III and DNA ligase then repair
What are the two types of excison repair in DNA
Base excision repair (BER): a single altered base is repaired
Nucleotide excision repair (NER): a chain of DNA containing the altered base is removed
