PROKARYOTIC AND EUKARYOTIC DNA DAMAGE DETECTION AND REPAIR MECHANISMS

DNA damage can occur due to various factors such as UV radiation, chemical agents, and errors during DNA replication. Both prokaryotic and eukaryotic cells have evolved intricate mechanisms to detect and repair DNA damage to maintain genomic integrity.

Prokaryotic DNA Damage Detection and Repair Mechanisms:

1. Direct Reversal: Some prokaryotes use direct reversal mechanisms to repair DNA damage. For instance, photolyases in bacteria can repair UV-induced DNA damage by directly reversing the damage caused by UV radiation.
2. Base Excision Repair (BER): This mechanism involves the removal of damaged bases by specific glycosylases, followed by the action of other enzymes to complete the repair process.
3. Nucleotide Excision Repair (NER): NER is a versatile repair mechanism used by prokaryotes to remove a wide range of DNA lesions caused by bulky adducts, chemical agents, and UV radiation.
4. Mismatch Repair (MMR): Prokaryotic cells utilize MMR to correct errors that occur during DNA replication, thereby preventing the accumulation of mutations.
5. SOS Response: In some prokaryotes, such as Escherichia coli, the SOS response is activated upon DNA damage. This response involves the upregulation of genes involved in DNA repair and mutagenesis.

Eukaryotic DNA Damage Detection and Repair Mechanisms:

1. Nucleotide Excision Repair (NER): Similar to prokaryotes, eukaryotic cells also employ NER to remove a wide range of DNA lesions caused by various factors including UV radiation.
2. Base Excision Repair (BER): Eukaryotic cells utilize BER to repair damaged bases in DNA, involving a series of enzymatic reactions to excise and replace the damaged bases.
3. Mismatch Repair (MMR): MMR in eukaryotes is crucial for correcting base-base mismatches and insertion-deletion loops that occur during DNA replication.
4. Homologous Recombination (HR): Eukaryotic cells use HR to repair double-strand breaks in DNA by utilizing an undamaged homologous sequence as a template for repair.
5. Non-Homologous End Joining (NHEJ): This mechanism is employed by eukaryotic cells to repair double-strand breaks in DNA without the need for a homologous template.
6. Cell Cycle Checkpoints: Eukaryotic cells have evolved cell cycle checkpoints that halt cell cycle progression upon detecting DNA damage, allowing time for repair before cell division proceeds.

In summary, both prokaryotic and eukaryotic cells possess sophisticated mechanisms for detecting and repairing DNA damage, ensuring the maintenance of genomic stability and integrity.

Effects of Radiation on Yeast DNA

Radiation can induce various types of damage to yeast DNA, including single-strand breaks, double-strand breaks, base modifications, and crosslinks. Ionizing radiation, such as X-rays and gamma rays, generates free radicals that can directly damage DNA or lead to the formation of reactive oxygen species, causing oxidative stress and additional DNA damage. Ultraviolet (UV) radiation primarily induces the formation of photoproducts, such as cyclobutane pyrimidine dimers and 6-4 photoproducts.

The study of radiation effects on yeast DNA provides valuable insights into the cellular responses to genotoxic stress. Yeast cells have conserved DNA repair pathways similar to those found in higher eukaryotes, making them an excellent model system for investigating the molecular mechanisms underlying radiation-induced DNA damage and repair.