Download Mutations

Mutations
Categories of Mutations by Type
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Deletions
Inversions
Insertions
Duplications
Point mutations
– Change of a single nucleotide in the DNA
• Nucleotide change – transition or transversion
• Single nucleotide insertion
• Single nucleotide deletion
Categories of Mutations by Affect
• Regulatory
– Affect production or steady state levels of gene
product
• promoters, splicing sequences, ribosome binding sites
• Structural (Coding)
– Affect actual sequence of gene product
• point mutations within coding sequence
• Silent
– a change in DNA sequence that has no detectable
affect on gene expression or gene product function
• SNP – single nucleotide polymorphisms
Point Mutations in Coding Sequences
Missense – changes amino acid
Nonsense – creates stop codon
Frameshift – alters remainder
of reading frame results in
completely different amino
acid sequence.
Base Changes
• Transitions
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pyrimidine replaces pyrimidine - C to T or T to C
purine replaces purine – G to A or A to G
GC changed to A=T or vice versa
Most common base change
• Transversion
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purine replaces pyrimidine or vice versa
G to C or T
A to C or T
C to G or A
T to G or A
GC changed to CG or T=A
Rare
Tautomeric
Shifts Lead to
Transitions
Figure 16.10
Tautomeric Base-Pairing
Normal
amino-A = keto-T
amino-C  keto-G
Tautomeric
imino-A = amino-C
amino-A = imino-C
enol-T  keto-G
keto-T  enol-G
Tautomeric Shifts Alter Base-Pairing Specificity
Tautomer
Figure 16.10
Modification of Bases by Alkylating Agents
EMS – ethylmethane sulfonate
DMS – Dimethyl sulfonate
ENU - Ethylnitrosourea
Alkylation Leads to Transitions
Deamination leads to Transitions
Oxidative DNA Damage Leads to
Transversion Mutations
free
radicals
Intercalation Leads to Insertions/Deletions
Ionizing Radiation
VIS
DNA Damage
Shortwave UV (UVA) Causes Thymidine
Dimers
X-rays & γ-rays Cause DNA Strand Breaks