Multiple Choice
Which of the following nitrogenous bases is found in DNA but not in RNA?
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7. DNA and Chromosome Structure
DNA Structure
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Which of the following accurately describes DNA base pairing and the number of hydrogen bonds formed between each pair?
A
Adenine pairs with Cytosine via 3 hydrogen bonds; Guanine pairs with Thymine via 2 hydrogen bonds.
B
Adenine pairs with Thymine via 2 hydrogen bonds; Guanine pairs with Cytosine via 3 hydrogen bonds.
C
Adenine pairs with Thymine via 3 hydrogen bonds; Guanine pairs with Cytosine via 2 hydrogen bonds.
D
Adenine pairs with Guanine via 2 hydrogen bonds; Thymine pairs with Cytosine via 3 hydrogen bonds.
Verified step by step guidance1
Recall the base pairing rules in DNA, which are based on complementary nitrogenous bases: Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C).
Understand that the number of hydrogen bonds between base pairs differs: A-T pairs form 2 hydrogen bonds, while G-C pairs form 3 hydrogen bonds.
Evaluate each option by matching the base pairs and the number of hydrogen bonds they form according to the rules: A-T with 2 bonds, G-C with 3 bonds.
Identify that any statement pairing Adenine with Cytosine or Guanine with Thymine is incorrect because these are not complementary pairs in DNA.
Conclude that the correct description is: Adenine pairs with Thymine via 2 hydrogen bonds; Guanine pairs with Cytosine via 3 hydrogen bonds.
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