Question

Three of the following DNA strands undergo a hyperchromic shift with a Tm of about 42°C. Which is the one with a Tm of 52°C?

A) ATGCAT
B) TAATGC
C) CGCGCG
D) GCGATC

Answer 1

The DNA strand with the Tm of 52°C is C) CGCGCG due to its high G-C content. Additionally, DNA has complementary strands where A pairs with T and G pairs with C. This fact is used to determine the sequence of a strand opposite to a given DNA segment.

Step-by-step explanation:

The question involves understanding the complementary strands of DNA nucleotides and concepts related to DNA denaturation and melting temperature (Tm).

The DNA strand with a higher proportion of G-C pairs has a higher Tm because guanine-cytosine base pairs form three hydrogen bonds, compared to adenine-thymine pairs which only form two.

Among the options given A) ATGCAT, B) TAATGC, C) CGCGCG, and D) GCGATC, the one with a Tm of 52°C is CGCGCG because it has the highest G-C content.

When the complementary strands of DNA are considered, A pairs with T, and G pairs with C, so the sequence 5'-ATTCCGGATCGA-3' will have a complementary strand: 5'-TAAGGCCTAGCT-3'. For a DNA segment with the sequence 5'-TCCATGAGTTGA-3', the complementary sequence would be 3'-AGGTACTCAACT-5'.