This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins bonds and structure, Subject name: Biochemistry
[{'content': 'How many amino acids are present in a single turn of a-helix? \nSelect and explain. \nA. 3.3, B. 3.6, C. 10.5, D. 11.5', 'role': 'user'}, {'content': 'Answer: B \nExplanation: a-helix is a rod-like helical structure where peptide backbone wound around a long axis, the side chains (R groups) radiate outward N-H group of one amino acid is hydrogen bonded to the C=O group of the amino acid located four residues earlier along the protein sequence. This hydrogen bonding creates a right-handed spiral or helix (coiled, rod-like structure). Most of the naturally occurring a-helix are right-handed. One turn of a-helix contains 3.6 amino acids. Distance between two adjacent amino acids is 1.5 Adeg', 'role': 'assistant'}]