Melting temperature of DNA is:-
**Core Concept**
The melting temperature of DNA is a critical parameter that determines the stability of the double helix structure. It is the temperature at which half of the DNA double helix is denatured, and the two strands separate. This temperature is influenced by the base composition of the DNA, specifically the percentage of guanine (G) and cytosine (C) bases.
**Why the Correct Answer is Right**
The melting temperature of DNA is directly related to the hydrogen bonding between the base pairs. The double helix is stabilized by the hydrogen bonds between adenine (A) and thymine (T) and between G and C. The melting temperature is higher when there are more G-C base pairs, as these base pairs have three hydrogen bonds, whereas A-T base pairs have only two. The correct answer is 69°C, which is the melting temperature for DNA with a G-C content of 50%.
**Why Each Wrong Option is Incorrect**
**Option A:** 45°C - This is too low, as it would not be possible for DNA to maintain its double helix structure at such a low temperature.
**Option B:** 85°C - This is too high, as it would be above the denaturation temperature of most DNA molecules.
**Option C:** 55°C - This is close, but not as high as the correct answer, as it would not reflect the increased stability of DNA with a higher G-C content.
**Clinical Pearl / High-Yield Fact**
The melting temperature of DNA is an important parameter in molecular biology, and it can be used to estimate the G-C content of a DNA sample.
**Correct Answer:** D. 69°C