Question

You are studying two strands of DNA. They have exactly the same length but the first one has a very high G +C/A + T ratio of 3.4. The second DNA strand has a G+ C/A +T ratio of 2.3. Which of the two strands will have the lowest melting temperature and why?

a. the first strand because it contains more H bonds
b. the second strand because it contains more H bonds
c. the first strand because it contains fewer H bonds
d. the second strand because it contains fewer H bonds
e. neither since their melting temperatures are the same.

Answer 1

The second DNA strand with a G+C/A+T ratio of 2.3 will have the lowest melting temperature because it contains fewer G+C base pairs, and therefore, fewer hydrogen bonds that need to be broken during denaturation compared to the first strand with a higher G+C/A+T ratio of 3.4.

Step-by-step explanation:

The melting temperature of DNA is influenced by the number of hydrogen bonds between the nitrogenous bases. Adenine (A) pairs with thymine (T) forming two hydrogen bonds, while cytosine (C) pairs with guanine (G) forming three hydrogen bonds. Therefore, a DNA strand with a higher G+C content will have a higher melting temperature as it contains more bonds that require more energy to break.

The second DNA strand, which has a G+C/A+T ratio of 2.3, will have the lowest melting temperature because it contains fewer G+C base pairs, and thus, fewer hydrogen bonds compared to the first DNA strand which has a G+C/A+T ratio of 3.4. The correct answer to the question is d. the second strand because it contains fewer H bonds.