MCAT Biochemistry Question 78: Answer and Explanation
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Question: 78
3. Which of the following DNA sequences would have the highest melting temperature?
- A. CGCAACCATCCG
- B. CGCAATAATACA
- C. CGTAATAATACA
- D. CATAACAAATCA
Correct Answer: A
Explanation:
The melting temperature of DNA is the temperature at which a DNA double helix separates into two single strands (denatures). To do this, the hydrogen bonds linking the base pairs must be broken. Cytosine binds to guanine with three hydrogen bonds, whereas adenine binds to thymine with two hydrogen bonds. The amount of heat needed to disrupt the bonding is proportional to the number of bonds. Thus, the higher the GC-content in a DNA segment, the higher the melting point.