Question

Which of the following oligonucleotides would have the highest melting point when paired with the proper complementary strand?

A. 5’-AAAAAAAA-3’
B. 5’- ATGCATGC-3’
C. 5’- CGCGCGCG-3’
D. 5’- TTTTGGGG-3’
E. 5’- TATATATA-3’

Answer 1

Strand C will have the highest melting point.

Explanation:

The melting point depends on the amount of H-Bonds that need to be broken in order for the two strands to be separatet. Remember that Adenin (A) forms a base pair with Thymin (T) which results in 2 H-Bonds, while Guanine (G) forms a base pair with Cytosine (C) which results in 2 H-Bonds.
By counting the number of H-Bonds you can determine which strand will have the highest melting point. The more H-Bonds there are, the more energy you need to break those intermolecular interactions and separate the 2 strands.