Passage V
When DNA is heated to its melting temperature (Tm) it denatures (breaks apart) into 2 strands. When cooled, the strands can relink to form less stable DNA, indicated by a lower Tm(see Figure 1).
Figure 2 shows how the absorbance of light by a solution of DNA molecules, each initially composed of 2 completely linked strands, varied as it was heated and then cooled. When the DNA began to denature, the absorbance increased sharply. When the DNA began to renature, the absorbance decreased sharply.
Figure 3 shows how Tm for heating varied for identical solutions of DNA previously exposed to UV light for different amounts of time.
Figures 1-3 adapted from Charles M. Lovett, Jr., Thomas N. Fitzgibbon, and Raymond Chang, "Effect of UV Irradiation on DNA as Studied by Its Thermal Denaturation." ©1989 by Division of Chemical Education, Inc., American Chemical Society.
24. The following DNA molecules each consist of 2 identical strands. Based on Figure 1, a solution of which DNA would most likely have the lowest melting temperature?
Your Answer is
Correct Answer is J
Explanation
The less the link between two DNA strands, the easier it is to decompose, so the lowest temperature24. The less the link between two DNA strands, the easier it is to decompose, so the lowest temperature