Multiple Choice
Which two components make up the backbone of a DNA molecule?
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7. DNA and Chromosome Structure
DNA Structure
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Which of the following pairs of double-stranded DNA molecules would have the lower melting temperature, and why?
A
A DNA molecule with 30% G-C content and a DNA molecule with 60% G-C content; the one with 30% G-C content has a lower melting temperature because G-C pairs form three hydrogen bonds, making the DNA more stable.
B
Melting temperature is independent of G-C content and depends only on the length of the DNA molecule.
C
Two DNA molecules with identical G-C content will always have different melting temperatures due to random sequence variation.
D
A DNA molecule with 60% G-C content and a DNA molecule with 30% G-C content; the one with 60% G-C content has a lower melting temperature because G-C pairs are less stable than A-T pairs.
Verified step by step guidance1
Understand that the melting temperature (Tm) of double-stranded DNA is the temperature at which half of the DNA molecules become single-stranded, reflecting the stability of the DNA double helix.
Recall that G-C base pairs form three hydrogen bonds, while A-T base pairs form only two hydrogen bonds, making G-C pairs more thermally stable.
Recognize that a higher percentage of G-C content in a DNA molecule generally increases its melting temperature because more energy is required to break the additional hydrogen bonds.
Compare the two DNA molecules: one with 30% G-C content and the other with 60% G-C content, noting that the molecule with 30% G-C content has fewer hydrogen bonds overall and thus lower stability.
Conclude that the DNA molecule with 30% G-C content will have a lower melting temperature than the one with 60% G-C content due to the difference in hydrogen bonding and stability.
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