Question

Given below are two statements:
Statement (I): Irradiation with UV light causes mutations in DNA
Statement (II): UV light causes formation of covalent bond between the thymine molecules on the same strand causing thymine dimerization
In light of the above statements,choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are true.
• B. Both Statement (I) and Statement (II) are false.
• C. Statement (I) is true but Statement (II) is false.
• D. Statement (I) is false but Statement (II) is true.

Hint:

UV radiation causes mutagenesis primarily by inducing the formation of covalent thymine dimers between adjacent pyrimidine bases on the same DNA strand.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Ultraviolet (UV) radiation is a common physical mutagen that damages DNA molecules, leading to replication errors and mutations if left unrepaired.

Step 2: Detailed Explanation:
Let us evaluate each statement describing UV-induced DNA damage:
Statement (I) states that UV irradiation causes mutations in DNA.
This is correct because UV light damages DNA, which can lead to base-substitution or deletion mutations during replication or error-prone DNA repair.
Thus, Statement (I) is true.
Statement (II) describes the molecular mechanism of this mutagenic activity.
Non-ionizing UV radiation (specifically UV-C and UV-B) is absorbed by pyrimidine bases in DNA.
This absorption excites electrons, leading to the formation of covalent bonds (specifically a cyclobutane ring) between adjacent thymine bases on the same strand of DNA.
This creates a thymine-thymine (T-T) dimer, distorting the double helix and blocking DNA replication and transcription.
Thus, Statement (II) is also true.
Because both statements are scientifically correct, the most appropriate choice is that both statements are true.

Step 3: Final Answer:
The correct option is (A).