8. All are characteristics of pyrimidines EXCEPT:(A) six membered ring.(B) heterocyclic.(C) conjugated.(D) fused five membered rings.(E) two nitrogens separated by a carbonyl.

7. DNA double helix structure is stabilized by all of the following EХСЕРТ:(A) the sugar-phosphate backbones are oriented in opposite directions.(B) the glycosidic bonds holding paired bases are directly across the helix from one another.(C) cations such as Mg2+ bind to the anionic phosphates.(D) bases stack together through hydrophobic interactions and van der Waals forces.(E) appropriate base pairing builds a polymer whose external dimensions are uniform.

8. All are characteristics of pyrimidines EXCEPT:
(A) six membered ring.
(B) heterocyclic.
(C) conjugated.
(D) fused five membered rings.

(E) two nitrogens separated by a carbonyl.

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