Which of the following statements is unique to proteins, & doesn't apply to either carbohydrates or lipids?

• A. Proteins are composed of a chain of similar molecules bonded together.
• B. Proteins contain an abundance of nitrogen.
• C. Proteins have a carbon-based backbone.
• D. Proteins contain carbon, hydrogen, and oxygen.

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the composition of proteins. Proteins are made up of amino acids, which are organic compounds containing carbon (C), hydrogen (H), oxygen (O), and nitrogen (N). Nitrogen is a key element that distinguishes proteins from carbohydrates and lipids.
2. Step 2: Review the composition of carbohydrates and lipids. Both carbohydrates and lipids are primarily composed of carbon (C), hydrogen (H), and oxygen (O), but they do not contain nitrogen in significant amounts.
3. Step 3: Analyze the options provided in the question. Identify which statement highlights a characteristic unique to proteins and not shared by carbohydrates or lipids.
4. Step 4: Eliminate incorrect options. For example, 'Proteins are composed of a chain of similar molecules bonded together' is not unique to proteins, as carbohydrates (e.g., polysaccharides) and lipids (e.g., triglycerides) also have similar molecular structures. Similarly, 'Proteins have a carbon-based backbone' and 'Proteins contain carbon, hydrogen, and oxygen' are not unique to proteins, as these characteristics are shared by carbohydrates and lipids.
5. Step 5: Conclude that the correct answer is 'Proteins contain an abundance of nitrogen,' as this is the unique feature that sets proteins apart from carbohydrates and lipids.