This document summarizes different types of DNA damage and repair systems. It discusses: 1) Mutations can be induced by external mutagens like physical agents (ionizing radiation, UV rays), chemical agents (alkylating agents, nitrosoamines), and biological agents (retroviruses). 2) Spontaneous mutations also occur naturally without external factors at rates of 10^10 per cell in prokaryotes and 10^6 in eukaryotes. 3) DNA damage can be repaired through direct repair mechanisms like photoreactivation which uses photolyase enzyme and visible light to remove pyrimidine dimers.

1. Presented by,
Mutation
Asst.Prof-Mr. Pradeep D. Devkate
M.Sc Microbiology, B.ED, MH-SET, 2-GATE (AIR 559), Ph.D. pursing.

3. DNA Damage and repair system
• Any kind of alteration or changes in genetic material and which was
transmit to one generation to next generation called Mutation.
or
alteration in DNA sequence or Single stranded or double stranded Break
or unusual covalent bonding among nucleotides.
SS cut Ds Cut Thymine=Thymine  Dimer formation

4. Mutation or DNA Damage
Induced Mutation
Inducing agents.
known external agents which is responsible for
DNA damage (Mutagen)
Agents=Physical, chemical, Biological
(Reterotransposons)..
Spontaneous Mutation
Naturally occur.
done without any known external
agents(Mutagen)
Spontaneous mutation Rate in prok=10^10
in euk= 10^6
Evolution is a slow gradual process because the spontaneous mutation rate is very low…..

5. Induced Mutation
Presence of known external factors (Mutagen).
1) Physical Agents---Radiation-
Ionizing and non ionizing radiation
Ionizing High energy Radiation
High strength Radiation
e.g- Gamma rays
X-Rays
Break ssDNA,dsDNA
• H2O H2O2 Reactive oxygen species.
• Low strength Radiation
• UV-Rays
• 260nm =UV-B this wavelength of
light was maximum absorb by
nitrogen base.
• Formation of pyrimidine
dimer(T=T,,C=C,,C=T)…and
cyclobutene ring formation ..
• DNA Replication Inhibition
• Transcription inhibition

6. Induced Mutation
2) Chemical Agents- base analogus=5 BU
Methylating agents or Alkylting Agents
Ethyl Methyl Sulfate(EMS) ,MMS.
Nitrosoamine
N-methyl –N’-Nitro-N-Nitrosoguandine
Transition Type of mutation
Purine= A,G
Pyrimidine= T,C, U(RNA)
Nitrogen
Base

7. Induced Mutation
3) Biological agents (Reterotransposons)
Insertional inactivation of gene.
Virus integrate DNA into Host Genome. Eg- Reteroviruses
Virus can play a role in causing cancer.

8. 3’ 3’
5’ 5’
Nucleotide=NB+d-R.S+P
Nucleoside= NB+R.S

9. Mutation
Gain of function
Loss of function

13. Direct Repair
Bacterial culture
UV light expose- T=T Dimer--/
Replication/Tncr
Death of bacteria
Visible light(blue light)
photoreactivation.
Chromophore group FAD active in presence
of blue light/visible light.
FAD bind to Photolyase Enzyme.
T=T dimer removed
Photolyase present
Bacteria to animals
except placental
mammals

18. Heat
,Alkline
pH,Tem

19. Uracil DNA glycosidase