Final answer:
DNA methylation is critical for DNA repair, particularly in the repair of methylated guanine bases and in mismatch repair, where it facilitates the identification of newly synthesized DNA for error correction. These methylation patterns also regulate gene expression and can be targets for drugs used in cancer treatment.
Step-by-step explanation:
DNA methylation plays a critical role in the DNA repair process. Certain types of DNA damage, such as the methylation of the guanine bases, are reversed by the protein methyl guanine methyl transferase (MGMT). When guanine is methylated, the MGMT protein transfers the methyl group from the guanine to itself, effectively repairing the guanine base. However, this process consumes the MGMT protein, making it a stoichiometric, one-time repair mechanism.
Another DNA repair process is mismatch repair, which occurs for errors that escape DNA polymerase's proofreading during replication. This system uses the newly synthesized, unmethylated DNA strand to identify and repair errors. This makes use of DNA's native methylation patterns, which are essential for epigenetic regulation of gene expression and inherited through generations.
The methylation patterns of DNA, especially within CpG islands in promoter regions, play a substantial role in regulating gene expression by silencing genes when methylated. This epigenetic control can be inherited, and when disrupted can be related to diseases such as cancer. Understanding these methylation patterns can therefore be crucial in both characterizing specific forms of cancer and designing drugs that alter these patterns to target and destroy cancer cells.