BABS1201 Lecture Notes - Lecture 14: Xeroderma Pigmentosum, Radon, Methylation
28 May 2018
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Mutation
DNA damage
• Genetic change is required for evolution
• Genetic stability is also required:
o Accurate replication of DNA
▪ For genetic information to be passed on to progeny
o Mechanisms for repairing DNA
Mutation - a change in the nucleotide sequence of an organism's DNA, ultimately creating genetic
diversity
E.g. British Peppered Moth (Biston betularia)
o Dark and light coloured moths
o Light coloured moths dominated
▪ Camouflaged with the tree bark
o Industrial area became polluted, black soot covered the trees
▪ Dark coloured moths dominated
o Light coloured moths dominated again when pollution levels subsided
o
Types of Mutations
• Point mutations - single base changes (substitution)
• Nucleotide insertion
• Nucleotide deletions
• Duplication of sequences
• Larger-scale chromosomal rearrangements
o Whole chromosome is rearranged
o Fusion, fission, inversion and translocation
• Mutations that occur in somatic cells do not get passed on,
• Mutations in gametes affects offspring
Causes of mutation
• Replication errors
o Nucleotide replication errors
o Parental strand is separated and replicated
▪ A base pair is mis-incorporated during replication
o Mutation becomes fixed when DNA is replicated again
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•
o DNA polymerase has an accuracy of 1 error in 10^7 nucleotides
o Proof-reading activity
▪ DNA mismatch repair
• Recognises mismatch
• Replaces with correct nucleotide
• Improves accuracy to 1:10^9
• Spontaneous damage
o DNA is susceptible to damage from the environment within the cell
▪ Inevitable
o Oxidative damage
▪ Cells require oxygen to breathe, produced as a by-product during the production of
ATP
▪ Oxygen produces oxygen free radicals
o Hydrolytic damage
▪ Within the aqueous environment
▪ Water breaks the bonds between base and sugar backbone
• Creates an abasic site (lacks a base)
o Methylation
▪ Methyl groups are added
▪ Causes DNA to be miscoded
•
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Dna damage: genetic change is required for evolution, genetic stability is also required, accurate replication of dna. For genetic information to be passed on to progeny: mechanisms for repairing dna. Mutation - a change in the nucleotide sequence of an organism"s dna, ultimately creating genetic diversity. British peppered moth (biston betularia: dark and light coloured moths, light coloured moths dominated, camouflaged with the tree bark. Industrial area became polluted, black soot covered the trees: dark coloured moths dominated, light coloured moths dominated again when pollution levels subsided. Types of mutations: point mutations - single base changes (substitution, nucleotide insertion, nucleotide deletions, duplication of sequences. Larger-scale chromosomal rearrangements: whole chromosome is rearranged, fusion, fission, inversion and translocation, mutations that occur in somatic cells do not get passed on, mutations in gametes affects offspring. Spontaneous damage: dna is susceptible to damage from the environment within the cell.
