Microbiology DNA Damage and Repair Mechanism Overview
Explore the intricate mechanisms of DNA damage and repair in microbiology, including causes of DNA damage and various repair systems such as direct repair, excision repair, and methyl-directed mismatch repair. Gain insights into how enzymes and processes repair different types of DNA damage, providing a comprehensive understanding of maintaining genetic stability.
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SRR & CVR Govt. Degree College (A) Vijayawada DEPARTMENT OF MICROBIOLOGY DNA Damage and Repair Mechanism DNA Damage and Repair Mechanism BY Dr. K. Aruna Lecturer in Microbiology SRR & CVR Govt. Degree College (A) Vijayawada 6/27/2025 1
DNA Damage and Repair Mechanism DNA Damage and Repair Mechanism Causes of DNA damage Causes of DNA damage 1. 1. Spontaneous mutations Spontaneous mutations 2. Induced mutation 2. Induced mutation Enzyme based repair systems Enzyme based repair systems 1. Direct repair or Light Dependent or Photo reactivation 2. Excision repair a). Base excision repair b). Nucleotide excision repair 3. Methyl Directed mismatch repair 4. Post replication or recombination repair mechanism 5. SOS repair 6/27/2025 2
DNA Damage and Repair Mechanism Direct repair or Light Dependent or Photo reactivation DNA Damage and Repair Mechanism 1. Direct repaid: DNA polymerase , 3- to -5 Exo nuclease proofreading activity Incorrect nucleotide id detected and removed Repair of UV-induced pyrimidine Dimers : Exposed to UV light in the wavelength of 320 to 370 nm Photolyase split the dimers Repair of Alkylation damage: Methylguanine methyltransferase : 6/27/2025 3
DNA Damage and Repair Mechanism 2. Excision repair a). Base excision repair : Glycosyase enzyme It recognize and cleave the bond between base and deoxy ribose sugar Other enzymes cleave bond between sugar and phosphate , releasing the sugar and leaving a gap in DNA strand, gap is filled by DNA polymearse and and DNA ligase b). Nucleotide excision repair (NER) or dark repair or excision repair removes thymine dimers and DNA distortions It involves four proteins, Uvr A, UvrB, UvrC and UvrD (Helicase) DNA polymerase I : fill the gap DNA ligase seals the final gap DNA Damage and Repair Mechanism 6/27/2025 4
DNA Damage and Repair Mechanism DNA Damage and Repair Mechanism 6/27/2025 5
3. Methyl Directed mismatch repair 6/27/2025 6
3. Methyl Directed mismatch repair 6/27/2025 7
DNA Damage and Repair Mechanism 4. Post replication or recombination repair mechanism DNA Damage and Repair Mechanism Rec A protein initiate the recombination between two sister strands 6/27/2025 8
DNA Damage and Repair Mechanism 5. SOS repair: last resort , emergency response SOS repair or bypass or Emergency repair is one of the DNA repair mechanisms introduced in 1975 by a scientist named Miroslav Radman. SOS repair primarily recovers the DNA damage caused due to environmental stresses. It serves as a regulatory system, which comprises many complex inducer proteins that repair the damaged DNA. SOS system also includes a repressor protein, namely LexA. The RecA protein floats around the cell, which regulates the activity of LexA protein. The RecA regulatory protein mediates the repression or expression of LexA repressor. Lex A it repress the transcription of 17 genes , involve in repair DNA Damage and Repair Mechanism In the presence of damage Rec A: which activates and stimulates the lex A 6/27/2025 9
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