This document summarizes several DNA repair mechanisms: mismatch repair removes errors that escape proofreading; base excision repair uses a base-flipping mechanism to remove damaged bases; nucleotide excision repair cleaves damaged DNA on either side of a lesion. It also discusses transcription coupled repair helping RNA polymerase past lesions, double strand break repair using homologous recombination, and photo reactivation using light energy to repair DNA. The document was authored by BHARATESHA.S for their 7th semester molecular biology course guided by CHANDRAKANTH.R.

1. BHARATESHA.S
7TH SEM
2014-15
GUIDED BY:
CHANDRAKANTH.R
MOLECULAR BIOLOGY DEPT.

2. CONTENTS
• Introduction
• Mismatch repair
• Base excision repair
• Nucleotide excision repair
• Transcription coupled DNA repair
• Double Strand Break repair
• Photo reactivation
• Conclusion
• References
• Acknowledgement

3. INTRODUCTION

4. Mismatch repair removes errors that escape
proofreading
★Increase the accuracy of DNA by an
additional 2-3 orders of magnitude
★Two challenges:
● Scan the genome rapidly
● Correct the mismatch accurately ( that is
it must recognize the newly synthesized
strand)

5. MutS scans the DNA,recognizing the mismatch from
the distortion they cause in the DNA backbone

7. Base excision repair enzymes remove damaged
bases by a base-flipping mechanism

8. Nucleotide excision repair enzymes cleave damaged
DNA on either side of the lesion

9. Transcription coupled DNA repair
Nucleotide excision repair system is capable of rescuing
RNA polymerase that has been arrested by the presence
of lesions in the DNA template

10. Double Strand Break repair model for homologous
recombination

11. Photo reactivation (the enzyme DNA photolyase
captures energy from light )

13. REFERENCES
I. James D.Watson, (2013)
Molecular biology of the gene 7th edition,
Cold Spring Harbour Laboratory Press,
New york- 313-324pp.
II. David L.Nelson, Michael M.Cox, (2011)
Principles of Biochemistry 5th edition ,
W.H.Freeman and Company,
New york- 993-999pp.

14. ACKNOWLEDGEMENT
I would like to thank my guide
Chandrakanth.R for his valuable guidance and
our course coordinator Dr.N.S.Devaki madam
for providing me this opportunity.