Question

Because hydrogen bonds hold the two strands of a DNA molecule together, the strands can be separated without breaking any covalent bonds. Every unique DNA molecule "melts" at a different temperature. In this context, Tm (melting temperature) is the point at which two strands separate, or become denatured. Assuming that all of the sequences below begin as stable double-stranded DNA molecules, which has the lowest melting temperature?

A) CAACTGG
B) TATGTCT
C) GACTCCTG
D) GGCGCACC

Answer 1

The sequence with the lowest G+C content will have the lowest melting temperature. Upon comparison, sequence B) TATGTCT has the lowest G+C content, thus the lowest melting temperature.

Step-by-step explanation:

The melting temperature (Tm) of DNA is influenced by its base-pair content, specifically the number of guanine (G) and cytosine (C) bases. These pairs are held together by three hydrogen bonds, while adenine (A) and thymine (T) are held together by two. Therefore, the DNA sequence with the highest G+C content will have the highest Tm, and the one with the lowest G+C content will have the lowest Tm.

Comparing the given sequences: A) CAACTGG - 3G/C pairs, B) TATGTCT - 1G/C pair, C) GACTCCTG - 4G/C pairs, D) GGCGCACC - 6G/C pairs. The sequence with the lowest number of G/C pairs, and consequently the lowest melting temperature, is B) TATGTCT.