Alpha helix and Beta pleated sheet are examples of: (A) Primary structure, (B) Secondary structure, (C) Teiary structure, (D) Quaternary structure
Answer is B. Regions of ordered secondary structure arise when a series of aminoacyl residues adopt similar phi and psi angles. Extended segments of polypeptide (example, loops) can possess a variety of such angles. The angles that define the two most common types of secondary structure, the ` helix and the a sheet, fall within the lower and upper left-hand quadrants of a Ramachandran plot, respectively. Ref: Harper's Illustrated Biochemistry, 30E (2015) pg no 38.