7) Which of the following statements best describes the location of the water mo

Question

7) Which of the following statements best describes the location of the water molecules in the crystal structure of the DNA double helix? [Hint: make the water molecules visible and color the DNA atoms and bonds gray.]

A) Water is found mostly in the interior of the double helix.

B) Water is found mostly on the exterior of the double helix.

C) Water is equally distributed in the interior and exterior of the double helix.

D) There are no water molecules in this structure.

8) When compared to the phosphodiester backbone, the interior of the double helix is ________.

A)polar

B)nonpolar

9)Crystallographic studies indicate H2O #91 (B 91 HOH) is hydrogen-bonded to the double helix. Which of the following atoms could serve as the hydrogen bond acceptor for this noncovalent interaction?

A) N6 of dA18 on chain B

B) O4 of dT19 on chain B

C) C7 of dT19 on chain B

D) N6 of dA6 on chain A

10) The hydrogen bond involving H2O #91 is located in the _____________ of the double helix.

A) minor groove

B) major groove

Explanation / Answer

7) (B) The DNA's double helix never occurs in isolation; instead, its entire surface is always covered by water molecules which attach themselves with the help of hydrogen bonds.

8) (B) The structure places the non-polar bases of DNA in the center of the double-stranded molecule, surrounded by the charged phosphate groups.

9) (A) (B) (D) Only Electronegative atoms can create hydrogen bonding.

10) (A) Minor groove

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