Question

A $\text{DNA}$ sample if first boiled for a few minutes and then cooled down then what will show :-

• A. Initial rise and then fall in UV absorbance
• B. Constant UV absorbance
• C. Initial drop and then rise in UV absorbance
• D. Steady drop in UV absorbance

Answer 1

The correct option is A Initial rise and then fall in UV absorbance

When a double-stranded $\text{DNA}$ is denatured, the stacked bases break apart and thus becomes less stable. It also absorbs more ultraviolet light since the bases no longer forms hydrogen bonds and therefore are free to absorb light. The phenomenon of $\text{UV}$ absorbance increases as $\text{DNA}$ is denatured, it is known as the hyper chromic shift. The purine and pyrimidine bases in $\text{DNA}$ strongly absorb ultraviolet light. Double-stranded $\text{DNA}$ absorbs less strongly than denatured $\text{DNA}$ due to the stacking interactions between the bases.
So, the correct answer is Initial rise and then fall in UV absorbance.