1. Presented By
Shouvik Mondal
Netaji Subhas Chandra Bose Institute of Pharmacy

2. Deoxyribonucleic acid (DNA) is a macromolecule that carries
genetic information from generation to generation. It is
responsible to preserve the identity of a species over
millions of year.

3. DNA damage is an alteration in Chemical structure of
DNA such as a break in a strand of DNA, a base missing
from the back of a DNA, or a chemically changed base.
Causes of DNA Damage
 Radiation
 Free Radicals
 Chemicals etc.

4. Types of DNA
Damage
G A CT
ds DNA Break
C-U deamination
AP site
Covalent X-linking
Thymidine dimer
ss Break
Mismatch

5. Major types of DNA Damage
Category Types
1. Single Base Alteration
Deamination
(C →U, A→ Hypoxanthine)
Depurination
Base Alkylanation
2. Two Base Alteration UV light induced pyrimidine dimer alteration
(T-T)
3. Chain Breaks Oxydative free radical formation
4. Cross Linkage
Between bases in the same or opposite
strands.
Between the DNA and protein molecules.

6. Mutation
•Transitions → Purine Purine
OR Pyrimidine Pyrimidine is
replaced
•Transversation → Purine
Pyrimidine OR Pyrimidine
Purine is replaced
PointMutation
•Insertion → Insert of base
•Deletion → Delete of base
Frameshit
Mutation

7. Mechanism of DNA
Repairing
1. •Base Excision Repair
2. •Nucleotide Excision Repair
3. •Mismatch Repair
4. •Double Stand Break Repair

8. BASE EXICISION REPAIR
The bases Cytosine, adenine
and guanine can undergo
spontaneous depurination to
respectively from Uracil,
hypoxanthine and xanthine.
These altered bases do not
exist in the normal DNA, and
therefore need to be removed.
This is carried out by base
exicision repair.

9. NUCLEOTIDE EXCISION
REPAIR
The DNA damage due to
ultraviolet light ionizing
radiation and other
environmental factors
often results in the
modification of certain
bases, strand breaks,
cross linkage, etc.
Nucleotide excision
repair is ideally suited for
such large scale defects
in DNA
Disease- Xerodrma
Pigmentosum

10. MISMATCH REPAIR
Disease- Hereditary Nonpolyposis Colon Cancer (HNPCC)

11. DOUBLE-STRAND
BREAK REPAIR
 Double Strand Breaks in DNA are dangerous.
 They result in genetic recombination which may lead
to chromosomal trans location, broken chromosomes
and finally cell death.
 DSBs can be repaired by homologous recombination
or non-homologous end Joining.

12. Thank You