Question:
Given below are two statements :
Statement (I): Irradiation of DNA with UV light cause formation of covalent bond between the thymine molecules on the same strand.
Statement (II): Thiamine dimerization in DNA caused by UV radiations can be reverted by Photo-reactivation.
In light of the above statements, choose the most appropriate answer from the options given below.
Given below are two statements :
Statement (I): Irradiation of DNA with UV light cause formation of covalent bond between the thymine molecules on the same strand.
Statement (II): Thiamine dimerization in DNA caused by UV radiations can be reverted by Photo-reactivation.
In light of the above statements, choose the most appropriate answer from the options given below.
Statement (I): Irradiation of DNA with UV light cause formation of covalent bond between the thymine molecules on the same strand.
Statement (II): Thiamine dimerization in DNA caused by UV radiations can be reverted by Photo-reactivation.
In light of the above statements, choose the most appropriate answer from the options given below.
Show Hint
Photoreactivation is a direct, error-free DNA repair mechanism found in bacteria, plants, and many animals, but is absent in placental mammals (including humans), which must rely on excision repair instead.
Updated On: Jul 23, 2026
- Both Statement (I) and Statement (II) are false.
- Both Statement (I) and Statement (II) are true.
- Statement (I) is true but Statement (II) is false.
- Statement (I) is false but Statement (II) is true.
Show Solution
Verified By Collegedunia
The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
Ultraviolet (UV) radiation is a physical mutagen that damages DNA structure.
Cells have evolved various DNA repair mechanisms, such as photoreactivation, to fix this UV-induced damage.
Step 2: Detailed Explanation:
Let us evaluate both statements:
- Statement (I): Exposing cells to UV light (specifically UV-B and UV-C) damages DNA.
It excites adjacent pyrimidine bases, primarily thymines, located on the same strand of DNA.
This excitation causes them to form covalent bonds with each other (cyclobutane rings), producing thymine dimers.
These dimers distort the DNA double helix, blocking replication and transcription.
Thus, Statement (I) is true.
- Statement (II): Pyrimidine dimerization (referred to in the exam as "thiamine dimerization") can be directly repaired by a process called photoreactivation.
This pathway uses the enzyme DNA photolyase, which binds specifically to the dimers.
When activated by absorbing visible blue light, photolyase uses this energy to break the covalent bonds of the dimer, restoring the original bases without damaging the phosphodiester backbone.
Thus, Statement (II) is true.
Therefore, both statements are correct.
Step 3: Final Answer:
Both Statement (I) and Statement (II) are true, corresponding to option (B).
Ultraviolet (UV) radiation is a physical mutagen that damages DNA structure.
Cells have evolved various DNA repair mechanisms, such as photoreactivation, to fix this UV-induced damage.
Step 2: Detailed Explanation:
Let us evaluate both statements:
- Statement (I): Exposing cells to UV light (specifically UV-B and UV-C) damages DNA.
It excites adjacent pyrimidine bases, primarily thymines, located on the same strand of DNA.
This excitation causes them to form covalent bonds with each other (cyclobutane rings), producing thymine dimers.
These dimers distort the DNA double helix, blocking replication and transcription.
Thus, Statement (I) is true.
- Statement (II): Pyrimidine dimerization (referred to in the exam as "thiamine dimerization") can be directly repaired by a process called photoreactivation.
This pathway uses the enzyme DNA photolyase, which binds specifically to the dimers.
When activated by absorbing visible blue light, photolyase uses this energy to break the covalent bonds of the dimer, restoring the original bases without damaging the phosphodiester backbone.
Thus, Statement (II) is true.
Therefore, both statements are correct.
Step 3: Final Answer:
Both Statement (I) and Statement (II) are true, corresponding to option (B).
Was this answer helpful?
0
0
Top ICAR AIEEA Plant Sciences Questions
- Both plant and animal cells contain some small organelles called 'peroxisomes', which are dedicated to the metabolism of substances such as
- Chemicals that store energy for the majority of work within cells are called
- The longest phase during the eukaryotic cell cycle is
- The formula: [Sum of (Observed-Expected)$^2$/Expected] is also known as
- Human beings have a large-sized 'proteome'. The principal and more significant reason for this is-
View More Questions
Top ICAR AIEEA Molecular Biology Questions
- Human beings have a large-sized 'proteome'. The principal and more significant reason for this is-
- The number of possible combinations in a polypeptide containing any 7 amino acids is given by the figure
Given below are two statements:
• [Statement (I):] Vertical resistance is exploited in agriculture by pathologists and breeders for crop improvement.
• [Statement (II):] Vertical resistance is mostly monogenic in nature.
In light of the above statements, choose the most appropriate answer from the options given below.
- Cannulae and Hami are the cellular structures found in
Given below are two statements, one is labelled as Assertion (A) and other labelled as Reason (R).
• [Assertion (A):] Deuteromycetes are known as 'Fungi Imperfecti'.
• [Reason (R):] In 'Deuteromycetes' only the asexual phase is known.
In light of the above statements, choose the correct answer from the options given below.
View More Questions
Top ICAR AIEEA Questions
- Which of the following statements is false?
- Which of the following is an example of an inventory?
- According to Adam Smith, productivity gains could be brought about through .
- The supply curve for an artificially scarce good is .
- Which of the following would not be considered an opportunity cost of paid employment?
View More Questions