Final answer:
DNA differs from RNA in that it contains the nitrogenous base thymine instead of uracil, has a double-stranded structure, and uses the sugar deoxyribose instead of ribose.
Step-by-step explanation:
The nucleic acid polymers DNA and RNA have several differences between them. One such difference is that DNA contains thymine while RNA contains uracil. Specifically answering the question, which of the following is true of DNA but not true of RNA: (a) It contains uracil, (b) It contains thymine, (c) It is single-stranded, (d) It has 5′-to-3′ directionality, the correct answer is (b) It contains thymine.
DNA is generally double-stranded with a double helix structure, whereas RNA is typically single-stranded. Furthermore, DNA's sugar is deoxyribose, while the sugar in RNA is ribose. These core distinctions help delineate their specific roles in the cell, with DNA storing genetic information and RNA playing direct roles in protein synthesis.