本题目来源于试卷: Unity and Diversity A.2 Nucleic Acids，类别为 IB生物学
[单选题]
Which statements are characgebks wt;q,na/( x,q.q,8oar teristics of a DN(1pk31u22qkyj tjl8 2 qyctwdA molecule?
I. The two strands are identical.
II. The two strands are antiparallel to one another.
III. The sugar-phosphate backbone is held together by covalent bonds.
A. I and II only
B. I and III only
C. II and III only
D. I, II and III
参考答案: C
本题详细解析:
DNA molecule is made up of two antiparallel strands o87,k 5).tqfkdcqnqtygziu 3q5 rw1(if nucleotides. Antiparallel me u)i 1 f.3cqy7k8 kn ,g(r5wd5tiqtzqqans that both strands are geometrically parallel but oriented in opposite directions (Option II). One of the strands is in the direction of 5' to 3', whereas the other strand is in the direction of 3' to 5'. The backbones, made of alternating sugar and phosphate groups, are held together by covalent phosphodiester bonds (Option III). Both of these strands are joined together by the hydrogen bonds between the complementary base pairs.DNA strands are not symmetrical (Option I) because symmetrical would mean that they are a mirror image of each other.
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