The document discusses the structure, damage, and repair mechanisms of DNA, outlining its significance as the genetic material in various organisms. It details types of DNA damage, such as single base changes and structural changes, and illustrates their causes and effects. Furthermore, it describes DNA repair mechanisms like mismatch repair, nucleotide-excision repair, and base-excision repair as essential systems to correct DNA injuries.

1. Submitted To: Submitted By:
SOS in Biotechnology Deepti Maheshwari
JIWAJI UNIVERSITY
DNA DAMAGEDNA DAMAGE
ANDAND
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 (4th
edition) by
David L. Nelson and Michael M. Cox
(page no. 966-975)
Principles Of Genetics (6th
edition) by D. Peter
Snustad and Michael J. Simmons
(page no. 347-350)