DNA mutations and repair Flashcards
(25 cards)
what can mutations affect
protein structure and function
what is a mutation
a permanent change to the nucleotide sequence in DNA
how do mutations arise
mistakes made during DNA replication
DNA damage from environmental agents
spontaneous hydrolytic reactions
mistakes made during DNA replication
mutation introduced by misincorporation of a base in first round of replication. in second round the mutation becomes permanently incorporated in the DNA sequence
DNA damage from environmental agents
eg nitrous acid
changing cytosine to uracil lead to a C-G –> T-A
eg. uv radiation
links carbons 5 and 6 of each ring to one another
intercalating agents
a planer molecule that can insert between two adjacent base pairs in a molecule of double-stranded
what is Ethidium bromide an example of ?
intercalating agents
what do intercalating agents lead to?
the incorporation of additional base on opposite strand
causes a frameshift mutation
spontaneous hydrolytic reactions
depurination results in the deletion of a base
does depurination break the phosphodiester bond ?
depurination does not break the phosphodiester bond
what are the three types of mutations?
point mutations
insertions
deletions
point mutations
single base pair change or substitution
what are the three types of point mutations
missense
nonsense
silent
missense
change in DNA sequence-changes amino acid encoded
nonsense
change in a coding region creates a stop codon
silent mutations
change in a coding region does not affect AA encoded
insertions
an extra base pair is inserted into the DNA
deletions
a base pair is deleted from the DNA
what does deletions result in
alters the codon
Changes the reading frame so all down stream codons are read out of frame
frame shift mutation
what does nuclease do in nucleotide excision repair ?
it hydrolyses 2 phosphodiester bonds, 1 on either side of the damage/distortion/thymine dimer and removes a single strand sequence of DNA
what does DNA polymerase do in nucleotide excision repair ?
reads the template strand and incorporates complementary nucleotides
what does DNA ligase do in nucleotide excision repair ?
catalyses the phosphodiester bond between the newly replaced DNA and the old DNA
Xeroderma pigmentosum
rare recessive disease
inability to repair DNA damage caused by UV light
no nucleotide excision repair
what are the results of xeroderma pigmentosum
multiple pigmented spots appear over the area of exposed skin
skin becomes wrinkled, dry and old
skin cancers develop
