Hello everyone, I am Dr. Ujwalkumar Trivedi, Head of Biotechnology Department at Marwadi University Rajkot. I teach Molecular Biology to the students of M.Sc. Microbiology and Biotechnology. The current presentation talks about the types of mutations, various mutagens and their mechanism of mutagenesis. The later part of the presentation describes various DNA repair mechanisms.

1. Presented by
Dr. Ujwalkumar Trivedi
Head
Department of Biotechnology
Marwadi University
Rajkot (Gujarat)

2. 1. Mutagenesis
• Mutation
• Replication Fidelity
• Mutagens
2. DNA Damage
• DNA lesions
• Oxidative Damage
• Alkylation
• Bulky Adducts
3. DNA Repair
• Photoreactivation
• Alkyltransferase
• Excision Repair
• Mismatch Repair
• SOS Repair
• Recombination Repair

3. Mutation
Replication
Fidelity
Mutagens
Mutagenesis

4. Mutation refers to a permanent, heritable
alterations in the base sequence of DNA
Reasons:
1. Spontaneous errors in DNA replication or meiotic
recombination.
2. A consequence of the damaging effects of physical
or chemical mutagens on DNA .

5. Transition : Purine or pyrimidine is replaced
by the other AG T C
Transversion: a purine is replaced by a
pyrimidine or vice verse
A T or C T  A or G
G T or C C  A or G
(A single base change)

6. •Noncoding DNA
•Nonregulatory DNA
•3rd position of a codon
Silent mutation
Coding DNA  altered Missense mutation
Phenotypic
effects
No
Coding DNA  stop codon
 truncated protein Nonsense mutation
Yes or No
Yes

7. Frameshift mutations
The translation of a protein encoded gene is
frameshifted , then changed the C-terminal side of the
mutation is completely changed.
The addition or loss of one or more bases in a DNA region

8. Example of Deletion Mutation and alteration
in coding frame

9. Rate of Mutation in Genomes
Bacteria: 3bp/1010bp
Humans: 1bp/1010bp
Rate of DNA replication
Prokaryotes: 1000bp/sec
Eukaryotes: 50bp/secs

10. Replication fidelity is Important to preserve the genetic information from
one generation to the next.
Mutation relevant
Spontaneous errors in DNA replication is very rare, one error per 1010 base
in E. coli.
Replication principle based on the base pairing is crucial to the high
accuracy of genetic information transfer
Protein (DNA Polymerase) involved in replication ensures high fidelity via
two mechanisms
1. Base Selection
2. Proofreading and real-time corrections.

11. 1. DNA polymerase: Watson-Crick base pairing
2. 3’ 5’ proofreading exonuclease.
3. RNA priming: proofreading the 5’ end of the lagging strand
4. Mismatch repair

12. Proof reading is mediated by
3’to 5’ exonuclease activity of
DNA polymerase

13. Mutation relevant
Cause DNA damage that can be converted to mutations.

14. Physical mutagens
High-energy ionizing radiation: X-rays and g-rays 
strand breaks and base/sugar destruction
Nonionizing radiation : UV light pyrimidine dimers
Chemical mutagens
Base analogs: direct mutagenesis
Nitrous acid: deaminates C to produce U
Alkylating agents
Intercalating agents
Lesions-indirect mutagenesis

16. 1.Base Analogues
2.Deamination Chemicals (Nitrous Acid)
3.Alkylating Agent
4.DNA Intercalating Agents

18. Nitrous acid: deaminates C to produce U, resulting in
G·C A·U

21. The great majority
of lesions
introduced by
chemical and
physical mutagens
are repaired by
one or more of
the error-free
DNA repair
mechanisms
before the lesions
is encounter by a
replication fork

32. The 360°
Education
Nurturing students for global care
Base Excision Repair

34. The 360°
Education
Nurturing students for global care
Nucleotide Excision Repair

37. The 360°
Education
Nurturing students for global care
Translesion Synthesis

42. Thank You
Kindly Reach us at:
Marwadi University
Rajkot-Morbi Highway Road, Gauridad, Rajkot, Gujarat 360003
Website: https://www.marwadieducation.edu.in/