Download A mutation can be defined as an alteration in DNA sequence. Types

A mutation can be defined as an alteration in
DNA sequence.
Types of mutation:
Point mutations
single base-pair substitution
Frameshift mutations
deletion or insertion of one or
more base pairs
Chomosomal aberrations
a major alteration in the structure
of a chromosome
Mutations can also be classified as
spontaneous or induced.
Point mutations – Base pair substitutions
Point mutations – Base pair substitutions
Effects at the polypeptide level
Point mutations – Base pair substitutions
Effects at the polypeptide level
Frameshift mutations – Insertions and
deletions
Effects at the polypeptide level
Processes that lead to spontaneous
mutations:
• Tautomeric shifts
• Changes in base structure
– deamination
– depurination
• Replication slippage – insertions and
deletions
Tautomeric shifts
Figure 16.2
Spontaneous mutation
Tautomeric shift
Deamination
Replication slippage - addition and deletion mutants
DNA looping
Induced mutations:
Base analogs as
mutagenic agents
Induced mutations – base analogs
Mechanism of mutation
5-bromouracil (5BU)
Induced mutations – base modifying compounds
Deamination by nitrous acid
Induced mutations – base modifying compounds
•Hydroxylamine is a hydroxylating agent that reacts only with cytosine
adding an OH group so that it pairs with adenine instead of guanine. Only
CG to TA transitions.
Induced mutations – intercalating mutagenic agents
(acridine dyes)
Induced mutations – intercalating mutagenic agents
Induced mutations – UV light
DNA repair
Repair of damaged bases or thymine dimers
1. Direct repair
2. Base excision repair (BER) and
nucleotide excision repair (NER)
Mismatch repair
Direct repair
Photoreactivation
enzyme
Ultraviolet repair genes