Explains why DNA must be repaired rather than discarded, and distinguishes DNA damage from mutation, with the common lesion types and the mutagens that cause them. Walks through the main repair pathways: direct reversal, base and nucleotide excision, mismatch repair, the several routes for double-strand breaks, and translesion synthesis. Closes with bacterial SOS and eukaryotic checkpoint responses and the genetic disorders linked to repair defects, including xeroderma pigmentosum, Bloom and Fanconi anaemia.
Topic 12 of 105 in the MU Sofia syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 7 sections, about 604 words (4 min of reading), with 10 flashcards.
In this note
DNA repair
Understanding DNA Repair
DNA Damage vs Mutation
Common Types of DNA Damage
Key DNA Repair Mechanisms
Global DNA Damage Responses
Genetic Disorders Linked to DNA Repair Defects
Understanding DNA Repair
DNA is constantly exposed to damage but cannot be discarded like RNA or proteins — it must be repaired.
Repairing DNA is essential for accurate cell function and reproduction.
Cells can experience thousands of DNA-damaging events daily — for instance, mammalian cells may get over 50,000 single-strand breaks a day.
If left unrepaired, this damage could threaten genome stability and cell survival.
Cells have developed various repair systems to detect and fix these problems.
DNA Damage vs Mutation
DNA Damage:
Refers to physical or chemical abnormalities in DNA structure.
It blocks processes like replication and gene expression.
It is usually incompatible with life if not repaired.
Mutation:
A change in the DNA sequence that still forms a stable DNA structure.
May look chemically normal but may not perform its original function.
Can result from repair attempts when the original sequence cannot be restored.
Mutagens (agents that cause DNA damage) include:
Physical factors: UV light, radiation.
Chemical factors: reactive oxygen species, alkylating agents.
Continue reading free
The whole note, all 7 sections, is free with an AceMed account, with its 10 flashcards. Premium adds flashcard recall, highlights and Ask AI.
