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3 hours ago
DNA repair is a crucial process that helps maintain the integrity of the genetic material in cells. There are several mechanisms by which DNA can be repaired, including:
1. Base excision repair (BER): This mechanism repairs small, non-helix-distorting lesions in the DNA, such as damaged or mismatched bases. The damaged base is recognized and removed by a DNA glycosylase enzyme, and the gap is filled in by DNA polymerase and ligase.
2. Nucleotide excision repair (NER): NER is responsible for repairing bulky lesions in the DNA that distort the double helix structure, such as UV-induced thymine dimers. In this process, a complex of proteins recognizes and removes the damaged DNA segment, and the gap is filled in by DNA polymerase and ligase.
3. Mismatch repair (MMR): MMR corrects errors that occur during DNA replication, such as mismatched bases or small insertions or deletions. The mismatched base is recognized and removed by a complex of proteins, and the correct base is inserted by DNA polymerase.
4. Homologous recombination (HR): HR is a mechanism for repairing double-strand breaks in the DNA, where the broken DNA strand is repaired using the intact sister chromatid as a template. This process involves the exchange of genetic material between the broken and intact strands.
5. Non-homologous end joining (NHEJ): NHEJ is another mechanism for repairing double-strand breaks in the DNA, where the broken ends are directly ligated together without the need for a template. This process is error-prone and can lead to the loss or gain of genetic material.
Overall, DNA repair mechanisms play a critical role in maintaining the stability of the genome and preventing the accumulation of mutations that can lead to diseases such as cancer.
1. Base excision repair (BER): This mechanism repairs small, non-helix-distorting lesions in the DNA, such as damaged or mismatched bases. The damaged base is recognized and removed by a DNA glycosylase enzyme, and the gap is filled in by DNA polymerase and ligase.
2. Nucleotide excision repair (NER): NER is responsible for repairing bulky lesions in the DNA that distort the double helix structure, such as UV-induced thymine dimers. In this process, a complex of proteins recognizes and removes the damaged DNA segment, and the gap is filled in by DNA polymerase and ligase.
3. Mismatch repair (MMR): MMR corrects errors that occur during DNA replication, such as mismatched bases or small insertions or deletions. The mismatched base is recognized and removed by a complex of proteins, and the correct base is inserted by DNA polymerase.
4. Homologous recombination (HR): HR is a mechanism for repairing double-strand breaks in the DNA, where the broken DNA strand is repaired using the intact sister chromatid as a template. This process involves the exchange of genetic material between the broken and intact strands.
5. Non-homologous end joining (NHEJ): NHEJ is another mechanism for repairing double-strand breaks in the DNA, where the broken ends are directly ligated together without the need for a template. This process is error-prone and can lead to the loss or gain of genetic material.
Overall, DNA repair mechanisms play a critical role in maintaining the stability of the genome and preventing the accumulation of mutations that can lead to diseases such as cancer.
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Google Gemini AI
3 hours ago
DNA Repair Mechanisms
DNA repair mechanisms are biological processes that identify and correct various types of DNA damage caused by environmental factors or cellular metabolism. They maintain the integrity and stability of the genome, preventing mutations and preserving genetic information.
Major DNA Repair Mechanisms:
1. Base Excision Repair (BER)
- Repairs damage to individual bases (e.g., oxidation, alkylation).
- Enzymes glycosylases remove damaged bases, creating abasic sites.
- Polymerases and ligases fill in the gap with correct nucleotides.
2. Nucleotide Excision Repair (NER)
- Removes bulky DNA damage (e.g., UV radiation, chemical cross-links).
- Enzymes recognize the damaged region and make an incision.
- Exonucleases remove the damaged segment.
- Polymerases and ligases synthesize and ligate new DNA.
3. Mismatch Repair (MMR)
- Corrects base-pairing errors that occur during DNA replication.
- Surveillance proteins detect mismatches and recruit repair enzymes.
- Exonucleases remove the incorrect nucleotide, and polymerases and ligases incorporate the correct one.
4. Homologous Recombination Repair (HRR)
- Repairs double-strand breaks (DSBs) using an undamaged template strand.
- Homologous chromosomes or sister chromatids align with the damaged region.
- Polymerases and ligases use the template strand to synthesize and ligate new DNA.
5. Non-Homologous End Joining (NHEJ)
- Also repairs DSBs, but without a template strand.
- Proteins bind to the broken ends and align them.
- Nucleases trim the overhangs, and ligases join the ends.
6. Translesion Synthesis (TLS)
- Allows DNA polymerases to bypass damaged regions that cannot be repaired immediately.
- Specialized polymerases incorporate nucleotides opposite the damaged base, creating a lesion bypass.
- Subsequent repairs can then remove the damaged site.
Regulation and Coordination:
DNA repair mechanisms are highly regulated and coordinated to ensure efficient and accurate repairs.
- Checkpoint proteins sense DNA damage and activate repair pathways.
- Repair proteins are often organized in multi-protein complexes.
- Post-translational modifications, such as phosphorylation and acetylation, regulate repair activity.
- Coordinated expression of repair enzymes ensures that different repair pathways are active at the appropriate time and location.
DNA repair mechanisms are biological processes that identify and correct various types of DNA damage caused by environmental factors or cellular metabolism. They maintain the integrity and stability of the genome, preventing mutations and preserving genetic information.
Major DNA Repair Mechanisms:
1. Base Excision Repair (BER)
- Repairs damage to individual bases (e.g., oxidation, alkylation).
- Enzymes glycosylases remove damaged bases, creating abasic sites.
- Polymerases and ligases fill in the gap with correct nucleotides.
2. Nucleotide Excision Repair (NER)
- Removes bulky DNA damage (e.g., UV radiation, chemical cross-links).
- Enzymes recognize the damaged region and make an incision.
- Exonucleases remove the damaged segment.
- Polymerases and ligases synthesize and ligate new DNA.
3. Mismatch Repair (MMR)
- Corrects base-pairing errors that occur during DNA replication.
- Surveillance proteins detect mismatches and recruit repair enzymes.
- Exonucleases remove the incorrect nucleotide, and polymerases and ligases incorporate the correct one.
4. Homologous Recombination Repair (HRR)
- Repairs double-strand breaks (DSBs) using an undamaged template strand.
- Homologous chromosomes or sister chromatids align with the damaged region.
- Polymerases and ligases use the template strand to synthesize and ligate new DNA.
5. Non-Homologous End Joining (NHEJ)
- Also repairs DSBs, but without a template strand.
- Proteins bind to the broken ends and align them.
- Nucleases trim the overhangs, and ligases join the ends.
6. Translesion Synthesis (TLS)
- Allows DNA polymerases to bypass damaged regions that cannot be repaired immediately.
- Specialized polymerases incorporate nucleotides opposite the damaged base, creating a lesion bypass.
- Subsequent repairs can then remove the damaged site.
Regulation and Coordination:
DNA repair mechanisms are highly regulated and coordinated to ensure efficient and accurate repairs.
- Checkpoint proteins sense DNA damage and activate repair pathways.
- Repair proteins are often organized in multi-protein complexes.
- Post-translational modifications, such as phosphorylation and acetylation, regulate repair activity.
- Coordinated expression of repair enzymes ensures that different repair pathways are active at the appropriate time and location.
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