Based on what you know of the peptide bonds that link together amino acid residues, why would proline's side chain reduce the flexibility of the backbone?

Verified step by step guidance

1. Step 1: Understand the structure of proline. Proline is unique among the 20 standard amino acids because its side chain forms a cyclic structure that includes the backbone nitrogen. This structure restricts the conformational freedom of the backbone.
2. Step 2: Understand the nature of peptide bonds. Peptide bonds are the chemical bonds that link amino acids together in a protein. They are formed by a dehydration reaction between the carboxyl group of one amino acid and the amino group of another.
3. Step 3: Understand the impact of proline's structure on peptide bonds. Because of its cyclic structure, proline introduces a fixed kink into the protein chain and restricts the flexibility of the backbone. This is because the nitrogen atom in the peptide bond lacks the ability to donate a hydrogen bond, which is crucial for the formation of secondary structures.
4. Step 4: Understand the role of flexibility in protein structure. The flexibility of the protein backbone is crucial for the protein to fold into its correct three-dimensional structure. The reduced flexibility due to proline can therefore impact the protein's structure and function.
5. Step 5: Summarize the answer. Proline's side chain reduces the flexibility of the backbone due to its unique cyclic structure that restricts the conformational freedom of the backbone and impacts the protein's ability to fold into its correct structure.