Multiple Choice
Which set correctly lists the four nitrogenous bases found in DNA?
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7. DNA and Chromosome Structure
DNA Structure
Multiple Choice
Which of the following best describes the structure of a DNA molecule?
A
A double-stranded, antiparallel helix composed of nucleotide chains with sugar-phosphate backbones and complementary base pairing (A with T, G with C)
B
A double-stranded, parallel helix composed of amino acids linked by peptide bonds
C
A single-stranded helical polymer made of ribose sugars and bases that pair A with U and G with C
D
A triple-stranded helix in which all bases pair identically (A with A, T with T, G with G, C with C)
Verified step by step guidance1
Step 1: Understand the basic components of DNA. DNA is made up of nucleotides, each consisting of a sugar (deoxyribose), a phosphate group, and a nitrogenous base (A, T, G, or C).
Step 2: Recognize the structure of DNA as a double helix, meaning it has two strands twisted around each other.
Step 3: Note that the two strands run in opposite directions, which is called antiparallel orientation. One strand runs 5' to 3', and the other runs 3' to 5'.
Step 4: Understand complementary base pairing: adenine (A) pairs with thymine (T) via two hydrogen bonds, and guanine (G) pairs with cytosine (C) via three hydrogen bonds. This pairing holds the two strands together.
Step 5: Differentiate DNA from other molecules: DNA is not composed of amino acids (which make proteins), nor is it single-stranded RNA (which pairs A with U), nor does it form triple helices with identical base pairing.
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