Final answer:
Damage to DNA bases from oxidative stress is predominantly repaired by Base Excision Repair, involving several steps that excise and replace the damaged base. Direct reversal methods are also employed for specific types of damage without the need for a template. These repair mechanisms are vital for cellular health and preventing mutations.
Step-by-step explanation:
DNA base damage from oxidative stress is primarily repaired through the Base Excision Repair (BER) mechanism. This process involves the recognition and excision of a damaged base by specific DNA glycosylases, followed by end processing, repair synthesis by DNA polymerase, and finally ligation by DNA ligase. Another important mechanism is the direct reversal of damage, such as the removal of abnormal bonds by photoreactivation or the reversal of methylated guanine bases by MGMT. These intricate systems of DNA repair ensure that cells can cope with the daily onslaught of DNA damage due to environmental factors and metabolic processes.
Reactive oxygen species can cause oxidation of bases, such as the formation of 8-oxo-7,8-dihydroguanine (8-oxoG), which is effectively repaired by BER. The importance of DNA repair mechanisms lies in preventing mutations that can lead to diseases such as cancer. These processes are highly conserved across evolution due to their critical role in maintaining genomic integrity.