5.Mutation of DNA and mechanisms involved in repairing DNA mutation

Answer 1

Mutation of DNA refers to any change or alteration in the sequence of bases within the DNA molecule. These changes can occur due to various factors, including errors during DNA replication, exposure to mutagens (such as radiation or certain chemicals), or processes like recombination and transposition.

There are several mechanisms involved in repairing DNA mutations, which help maintain the integrity and stability of the genetic material. Some of the major DNA repair mechanisms include:

1. Mismatch repair (MMR): MMR corrects errors that occur during DNA replication, where the wrong base is incorporated into the newly synthesized DNA strand. MMR proteins recognize and remove the mismatched base, followed by re-synthesis and ligation of the correct base.

2. Base excision repair (BER): BER repairs damaged or modified bases in the DNA. DNA glycosylases recognize and remove the damaged base, creating an apurinic/apyrimidinic (AP) site. AP endonucleases then cleave the DNA backbone near the AP site, followed by replacement of the correct base and subsequent ligation.

3. Nucleotide excision repair (NER): NER repairs bulky DNA lesions, such as those caused by UV radiation or certain chemical compounds. NER proteins scan the DNA for lesions, remove a stretch of nucleotides encompassing the lesion, and then synthesize and ligate new DNA in the gap.

4. Homologous recombination (HR): HR repairs DNA double-strand breaks (DSBs) and large-scale DNA damage. It involves the exchange of genetic material between homologous DNA molecules, either between two sister chromatids or between homologous chromosomes.

5. Non-homologous end joining (NHEJ): NHEJ repairs DNA DSBs by directly ligating the broken ends of the DNA molecule. It is a rapid but potentially error-prone repair pathway, as it can lead to small insertions or deletions at the repaired site.

6. Translesion synthesis (TLS): TLS is a DNA damage tolerance mechanism that allows replication to continue in the presence of DNA lesions. Specialized DNA polymerases can bypass the lesion and insert a non-specific base, which may cause a mutation but allows for bypassing the damage.

These DNA repair mechanisms play crucial roles in maintaining the fidelity and stability of the genetic material in cells. However, if the repair mechanisms fail or are overwhelmed, DNA mutations can persist, leading to various genetic disorders, cancer, or evolutionary changes.