Final answer:
Homologous recombination and nucleotide excision repair are DNA repair mechanisms involving both DNA strands, activated by DNA damage such as double-stranded breaks and pyrimidine dimers, ensuring genome integrity and preventing mutations.
Step-by-step explanation:
Repair mechanisms that involve both strands of DNA are homologous recombination and nucleotide excision repair. Both of these mechanisms are activated by DNA damage, such as incorrect bases or thymine dimers often caused by environmental factors like ultraviolet light. Homologous recombination deals with the repair of double-stranded breaks using sister chromatids or homologous chromosomes to ensure accurate DNA repair. Nucleotide excision repair removes damaged bases by making cuts on both sides of the abnormal base and then filling in the correct nucleotides.
Homologous recombination can repair a double-stranded DNA break with the assistance of several enzymes and proteins. Nucleotide excision repair is particularly important for repairing pyrimidine dimers, which result from UV exposure and involve enzymes that make cuts around the damaged bases to remove and replace them. This process is vital to maintaining the integrity of genetic information and preventing potential mutations that could lead to conditions such as skin cancer.