DNA damage and repair mechanism

The presentation briefs about the ways in which the DNA can get damaged and what are the mechanisms through which it gets repaired.

1. Submitted To: Submitted By:


SOS in Biotechnology Deepti Maheshwari
Jiwaji University M.Sc. 2
nd
Semester
JIWAJI UNIVERSITY
DNA DAMAGE DNA DAMAGE
AND AND
REPAIR MECHANISMREPAIR MECHANISM

2. CONTENTS:
Introduction
Structure of DNA
DNA Damage
DNA Repair

3. INTRODUCTION
DNA makes up the genetic material in
prokaryotes, eukaryotes and some viruses
also.
 It is the ultimate source of biological information.
The shapes and activities of individual cells are, to
a large extent, determined by genetic instructions

contained in DNA.

They carry the information in the form that can be
passed from one generation to another.

4. STRUCTURE OF DNA:

5. It is an event that introduces a deviation from the
usual double-helical structure of DNA.



DNA DAMAGE:
 Single Base Changes Structural Changes
DNA damage can lead to :
•Conversion of one base to another
•Affect the DNA sequence.
•Does not interferes with the process
of replication or transcription and
translation
•E.g.(a) Deamination of cytosine to
uracil
(b) Insertion of adenine in place
of cytosine.
•Change in the structure of
DNA occurs.
•Physical impediment to the
process of replication or
transcription.
E.g.(a) Formation of thymine

dimers.
(b) Methylation of a
base.

6. FIG: (A ) Mismatched base pairing

between U and G
FIG: (B ) Mismatched base pairing

between A and G
Cause : NITROUS ACID, causes
oxidative deamination of the
amino groups in cytosine.
Cause: REPLICATION ERROR
which inserts adenine in place of
cytosine.
EXAMPLES OF SINGLE BASE CHANGES IN DNA:

7. EXAMPLES OF STRUCTURAL CHANGES IN DNA :
FIG: (A ) Dimer formation between
adjacent thymine dimers
FIG: (B) Addition of methyl group
to guanine
Cause :UV IRRADIATION causes
dimers which blocks the
replication process.
Cause : ALKALYTING AGENTS
causes methylation of guanine.

8. DNA REPAIR:
Injury to DNA is minimized by DNA repair systems
that recognize and correct the damage.
In Escherichia coli , following type of DNA repair
mechanisms exist:
1.) Mismatch repair mechanism
2.) Nucleotide-excision repair mechanism
3.) Base-excision repair mechanism

9. 1.) Mismatch repair mechanism:
Fig: Early steps of
methyl-directed
mismatch
repair.

10. Fig: Completing methyl-directed mismatch repair.
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11. 2.) Nucleotide-excision repair mechanism:

13. 3.) Base-excision repair mechanism:

15. REFRENCES:
GENES VII by Benjamin Lewin
(page no. 447-453)
Principles Of Biochemistry (4
th
edition) by
David L. Nelson and Michael M. Cox
(page no. 966-975)
Principles Of Genetics (6
th
edition) by D. Peter
Snustad and Michael J. Simmons
(page no. 347-350)