Question

In which of the following will DNA melt at the lowest temperature?

• A. $5′-AATAAAGC-3′ \\ 3′-TTATTTCG-5′$
• B. $5′-AATGCTGC-3′ \\ 3′-TTACGACG-5′$
• C. $5′-ATGCTGAT-3′ \\ 3′-TACGACTA-5′$
• D. $5′-GCATAGCT-3′ \\ 3′-CGTATCGA-5′$

Answer 1

Answer: (A)

In a double helix structure of DNA the bases in the two complimentary strands are paired with the help of hydrogen bonds. There are two hydrogen bonds between one adenine and thymine base pairs where as there are three hydrogen bonds between one guanine and cytosine base pairs. The energy required to break the bond between G-C will be more as compared to energy required for A-T bonds. So the DNA with maximum number of A-T pairing will melt faster at lower temperature as compared to others.