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 best statement that 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." This statement highlights the differences in nitrogenous bases, specifically the presence of uracil in RNA, which is a key chemical difference between the two molecules.

Step 1: Overview of DNA and RNA structures

DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are both nucleic acids that store genetic information. They share a three-component structure, consisting of a phosphate group, a sugar molecule, and a nitrogenous base. The key differences between DNA and RNA lie in the sugar and nitrogenous base components.

Step 2: Analyze statement (a)

Statement (a) claims that DNA has two different sugars in its sugar-phosphate backbone, while RNA only has one. This statement is incorrect. Both DNA and RNA contain only one type of sugar; DNA has deoxyribose and RNA has ribose.

Step 3: Analyze statement (b)

Statement (b) focuses on the nitrogenous bases, stating that thymine is present in DNA, while RNA contains a similar base with one less methyl group. This statement is accurate; thymine is found in DNA, while RNA contains uracil, which is identical to thymine but lacks a methyl group.

Step 4: Analyze statement (c)

Statement (c) states that the RNA sugar-phosphate backbone contains fewer oxygen atoms than DNA's backbone. This statement is incorrect; RNA actually contains more oxygen atoms in its backbone due to the presence of the hydroxyl group on the ribose sugar.

Step 5: Analyze statement (d)

Statement (d) says that DNA forms double helices but RNA cannot. This statement is partially correct, as DNA does form a double helix structure, while RNA usually forms a single-stranded structure. However, RNA can also form complex secondary and tertiary structures, including double-stranded regions. Thus, this statement does not focus on the chemical differences between DNA and RNA.

Step 6: Select the best statement

Based on the analysis of each statement, the best explanation of the chemical differences between DNA and RNA is found in statement (b): "Thymine is one of the DNA bases, whereas RNA's corresponding base is thymine minus a methyl group." This statement addresses both the differences in nitrogenous bases (key components of nucleic acids) and the presence of uracil in RNA, which is a direct chemical difference between the two molecules.