Which of the following statements about the two strands of a DNA molecule is true?
Select one:
A. The strands are a pair of sister chromatids.
B. The strands are connected to each other by sugar-phosphate bonds.
C. A T base on one strand always pairs with an A base on the other strand.
D. An A base on one strand always pairs with a G base on the other strand.
E. The strands have identical base sequences.
Answer (2)
The two strands of a DNA molecule are connected to each other by sugar-phosphate bonds. Each DNA strand is comprised of a sugar-phosphate backbone, with nitrogenous bases protruding from the backbone. The bases of the two strands pair up in a complementary manner; adenine (A) always pairs with thymine (T) and guanine (G) always pairs with cytosine (C). These base pairings are stabilized by hydrogen bonds, with A-T forming two hydrogen bonds and G-C forming three hydrogen bonds. Therefore, option B is the correct statement.
The correct statement is C: A T base on one strand always pairs with an A base on the other strand. The DNA strands are held together by hydrogen bonds that connect complementary bases. The strands are not identical; rather, they are complementary, following specific pairing rules: A-T and G-C.
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