Biology Qbank 1 #5

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Biology Qbank 1 #5

Post by NS_Tutor_Will » Tue Aug 14, 2018 11:04 am

A student stated about this question: "Even though DNA is stabilized through hydrogen bonding, hydrophobic interactions between DNA and water are also responsible for stability. The center of DNA consisting of nucleotides is non-polar which prevents disassociation of DNA within water. This is a hydrophobic interaction."

While it is true that there are hydrophobic interactions between nitrogenous bases (non-polar portions) and water (polar solvent), in this case one of the answer choices stipulates "DNA forms a double helix that is held together by hydrophobic interactions between the nitrogenous bases." In this case, that answer choice is incorrect because there are not hydrophobic interactions between nitrogenous bases. Between nitrogenous bases there are hydrogen bonds (three between G & C, two between A & T). Because this answer specifies that the interactions must be between nitrogenous bases, it is false.

If the answer choice had stated that hydrophobic interactions help stabilize DNA, then it would be true. But these hydrophobic interactions are not between nitrogenous bases, they are between nitrogenous bases and water.

Good luck!

Update: After further consultation with the content team, we've decided to revise this question to avoid potential ambiguity about hydrophobic interactions and to explicitly recognize the role of base stacking in DNA's structure and stability.
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