Final answer:
Cells possess DNA repair mechanisms such as direct reversal to prevent permanent mutations by chemically reversing damage to DNA. Processes like photoreactivation and the use of enzymes like MGMT repair specific types of damage like thymine dimers and DNA methylation, respectively.
Step-by-step explanation:
DNA Repair Mechanisms
Cells have developed various mechanisms to repair damage to our hereditary material and prevent permanent mutations. Direct reversal is a type of DNA repair process where damage is chemically reversed without the need for a template. For example, the enzyme photolyase can directly reverse the formation of thymine dimers, which are caused by UV light and result in abnormal covalent bonds between adjacent thymidine bases. This process, called photoreactivation, requires blue/UV light to activate the photolyase enzyme for catalysis.
Another mechanism involves the enzyme methyl guanine methyl transferase (MGMT) which directly reverses methylation of guanine bases. Since each MGMT molecule can be used only once, this process is considered expensive for the cell. Similarly, certain methylations of cytosine and adenine are directly reversed by the cell's repair mechanisms.
These repair processes are vital as they rectify the damage before cell division, preventing the passing on of mutations to daughter cells, which would make the original DNA sequence unrecoverable. While DNA polymerases have proofreading abilities to correct incorrect bases during replication, additional repair systems such as mismatch repair further prevent mutations. It is essential to fix these errors to avoid consequences like cancer and to maintain the integrity of genetic information.