- Excessive ultraviolet (UV) radiation is harmful to life. The damage caused to the biological systems by ultraviolet radiation is by:
a) Inhibition of DNA synthesis
b) Formation of thymidine dimers
c) Ionization
d) DNA fragmentation
Explanation:
Exposure of cell to ultra-violet light can result in the covalent joining of two adjacent pyrimidines usually thymines producing a dimmer.
These thymine dimmers prevent DNA polymerase from the replicating the DNA strand beyond the site of dimmer formation.
Important point:
First a UV specific endo-nuclease also called UV specific excinuclease recognizes the dimmer and cleaves the damage strand. Damaged oglio-nucleotide is released.
Answer: Formation of thymidine dimers
Ref: Harper 30th Ed. Page-