Final answer:
DNA repair mechanisms are vital for genome integrity, with nucleotide excision repair being one method that involves replacing incorrect nucleotides and sealing the site with a phosphodiester bond. Factors like cellular age and type affect repair rates, and ineffective repair can lead to cellular senescence.
Step-by-step explanation:
DNA repair mechanisms are critical for maintaining the integrity of the genome. The types of molecules involved and the mechanism of repair depend on the type of damage and the cell cycle phase. In eukaryotic cells, routine repair occurs with little consequence due to the non-coding regions of the genome.
In some cases, like in older cells, there can be thousands of repair 'footprints' per cell, indicative of the repair system's activity. DNA repair mechanisms include nucleotide excision repair, which involves removing incorrect bases flanked by cuts on both the 3' and 5' ends. The gap is then filled in with correct nucleotides and sealed with a phosphodiester bond by DNA ligase. Cellular age, cell type, and environmental factors can affect the rate of DNA repair. When cells fail to repair DNA effectively, they may enter senescence, a state of irreversible dormancy.