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345x Filetype PPTX File size 0.42 MB Source: www.colmed-alnahrain.edu.iq
MUTAGENESIS
DNA DAMAGE
DNA REPAIR
RECOMBINATION
MUTAGENESIS
Mutations
Mutations are heritable permanent changes
in the base sequence of DNA.
Point mutations may be transitions (e.g.
GC→AT) or transversions (e.g. GC→TA).
Deletions and insertions involve the loss or
addition of bases and can cause frameshifts
in reading the genetic code. Silent mutations
have no phenotypic effect, while missense
and nonsense mutations change the amino
acid sequence of the encoded protein.
Replication fidelity
The high accuracy of DNA replication
10
(one error per 10 bases
incorporated)
depends on a combination of proper
base pairing of template strand and
incoming nucleotide in the active
site of the DNA polymerase,
proofreading of the incorporated
base by 3→5 exonuclease and
mismatch repair.
Physical mutagens
Ionizing (e.g. X- and -rays) and
nonionizing (e.g. UV) radiation
produce a variety of DNA lesions.
Pyrimidine dimers are the
commonest product of UV
irradiation.
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