DNA DAMAGE

AND REPAIR

By Souvik Pal

B.Pharm, 6th Sem

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 air.

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.

Types of DNA Damage

SummarisedG A CT

ds DNA BreakC-U deamination

AP siteCovalent X-linking

Thymidine dimer

ss Break

Mismatch

Major types of DNA Damage

Category Types

Single Base Alteration

Deamination (C →U, A→ Hypoxanthine)

DepurinationBase Alkylanation

Two Base Alteration UV light induced pyrimidine dimer alteration (T-T)

Chain Breaks Oxydative free radical formation

Cross LinkageBetween bases in the same or opposite strands.Between the DNA and protein molecules.

Mutation refers to a change in DNA structure of gene

Point Mutation•Transitions → Purine Purine OR Pyrimidine Pyrimidine is replaced•Transversation → Purine Pyrimidine OR Pyrimidine Purine is replaced

Frameshit Mutation

•Insertion → Insert of base•Deletion → Delete of base

Mechanism of DNA Repairing

1. •Base Excision Repair

2. •Nucleotide Excision Repair

3. •Mismatch Repair

4. •Double Stand Break Repair

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.

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

MISMATCH REPAIR

DOUBLE-STRAND BREAK REPAIR