Problem 80 - Chemistry: The Central Science

Question

Which statement best explains the chemical differences between DNA and RNA? (a) DNA has two different sugars in its sugar-phosphate backbone, but RNA only has one. (b) Thymine is one of the DNA bases, whereas RNA's corresponding base is thymine minus a methyl group. (c) The RNA sugar-phosphate backbone contains fewer oxygen atoms than DNA's backbone. (d) DNA forms double helices but RNA cannot.

Step-by-Step Solution

Answer

The correct answer is (b) Thymine is one of the DNA bases, whereas RNA's corresponding base is thymine minus a methyl group.

Step 1: Evaluate statement (a)

Statement (a) says DNA has two different sugars in its sugar-phosphate backbone, but RNA only has one. This is incorrect because both DNA and RNA contain only one type of sugar in their sugar-phosphate backbone: deoxyribose and ribose, respectively.

Step 2: Evaluate statement (b)

Statement (b) refers to the bases of DNA and RNA, stating that thymine is one of the DNA bases and the corresponding RNA base is thymine minus a methyl group. This is a correct statement because thymine is indeed a base in DNA, and its corresponding base in RNA is uracil, which lacks a methyl group.

Step 3: Evaluate statement (c)

Statement (c) says that the RNA sugar-phosphate backbone contains fewer oxygen atoms than DNA's backbone. This statement is incorrect; in fact, it's the other way around. The sugar in RNA, ribose, has one more oxygen atom than the sugar in DNA, deoxyribose.

Step 4: Evaluate statement (d)

Statement (d) claims that DNA forms double helices but RNA cannot. This statement is not entirely accurate. While it is true that DNA usually forms double helices, RNA can also form double helices in some cases, such as in its secondary structure or when forming double-stranded RNA molecules. In conclusion, the statement that best explains the chemical differences between DNA and RNA is: (b) Thymine is one of the DNA bases, whereas RNA's corresponding base is thymine minus a methyl group.