1. Which of the following best describes the term 'peptide chain' in the context of amino acid groups?

• A. A circular arrangement of amino acids forming a ring structure
• B. A single amino acid with a modified side chain
• C. A group of amino acids with similar side chain properties
• D. A linear sequence of amino acids linked by peptide bonds

Answer: (D)

Verified step by step guidance

1. Understand the term 'peptide chain': A peptide chain refers to a linear sequence of amino acids that are covalently linked together by peptide bonds. Peptide bonds are formed through a condensation reaction between the carboxyl group (-COOH) of one amino acid and the amino group (-NH2) of another amino acid.
2. Clarify the structure: Unlike circular arrangements or single amino acids, a peptide chain is a linear structure. It has a defined directionality, starting with the amino (N-) terminus and ending with the carboxyl (C-) terminus.
3. Eliminate incorrect options: The first option, 'A circular arrangement of amino acids forming a ring structure,' describes a cyclic peptide, which is not the same as a peptide chain. The second option, 'A single amino acid with a modified side chain,' refers to an individual amino acid, not a chain. The third option, 'A group of amino acids with similar side chain properties,' describes a classification based on side chain characteristics, not a peptide chain.
4. Focus on the correct definition: The correct answer is 'A linear sequence of amino acids linked by peptide bonds,' which accurately describes the structure and formation of a peptide chain.
5. Relate to biological significance: Peptide chains are fundamental components of proteins, which are essential macromolecules in biological systems. Proteins are formed when one or more peptide chains fold into specific three-dimensional structures.