What type of β-sheet is presented in the figure below? Draw all hydrogen bonds between appropriate groups.

• A. Antiparallel β-sheet.
• B. Parallel β-sheet.

Answer: (A)

Verified step by step guidance

1. Examine the orientation of the polypeptide chains in the image. In an antiparallel β-sheet, the N-terminus of one strand aligns with the C-terminus of the adjacent strand, while in a parallel β-sheet, the N-termini and C-termini of adjacent strands align.
2. Identify the direction of the peptide bonds in each strand. In the image, observe that the peptide bonds in one strand are oriented in the opposite direction to those in the adjacent strand, indicating an antiparallel arrangement.
3. Look for the hydrogen bonding pattern between the strands. In antiparallel β-sheets, hydrogen bonds are formed between the carbonyl oxygen of one amino acid and the amide hydrogen of the adjacent strand, typically in a straight line.
4. Draw the hydrogen bonds between the carbonyl oxygen of one strand and the amide hydrogen of the adjacent strand. Ensure that these bonds are perpendicular to the direction of the strands, characteristic of antiparallel β-sheets.
5. Conclude that the β-sheet in the image is antiparallel based on the opposite orientation of the strands and the linear hydrogen bonding pattern between them.