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Given below are two statements
Statement (I) : DNA usually absorbs maximum at 260 nm, entirely due to its aromatic bases
Statement (II) : On denaturation, DNA's ultraviolet absorbance decreases by nearly 40%, though the absorbance maximum
wavelength remains the same
In light of the above statements, choose the most appropriate answer from the options given below.
EXPLANATION
DNA & RNA Structure, Replication, & Repair
- Statement (I) is True: Native nucleic acids exhibit maximum UV absorbance at 260 nm ($A_{260}$) driven by the conjugated $\pi$-electron systems of the purine (adenine, guanine) and pyrimidine (cytosine, thymine) aromatic heterocyclic bases.
- Statement (II) is False: Thermal or alkaline denaturation of double-stranded DNA into single strands disrupts base stacking, resulting in hyperchromicity—an increase in absorbance by 30 to 40% at 260 nm, rather than a decrease.
- Conclusion: Statement (I) is true but Statement (II) is false.
Correct option: (3) Statement (I) is true but Statement (II) is false.
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