132. Cis-peptide unit corresponds to the O-C-N-H dihedral angle (degrees) of:
1. 0
2. -60
3. 120
4. 180

Question

Cis-peptide unit corresponds to the O-C-N-H dihedral angle (degrees) of:

1. 0

2. -60

3. 120

4. 180

Detailed Explanation

In the study of protein structure, the peptide bond between amino acids plays a critical role in the conformation of the protein chain. The dihedral angle refers to the angle between two planes formed by four atoms: O-C-N-H. This angle can help classify the cis and trans configurations of the peptide bond.

• Cis-Peptide Bond: In a cis-peptide bond, the alpha-carbon atoms on both sides of the bond are on the same side. The dihedral angle for this configuration is much smaller than for the trans-peptide bond.

• Trans-Peptide Bond: In a trans-peptide bond, the alpha-carbon atoms are on opposite sides of the peptide bond, which is energetically more favorable in most proteins.

The O-C-N-H dihedral angle (denoted by ω for omega) is an important angle in protein structure:

• The dihedral angle in a cis-peptide bond corresponds to 0 degrees or a very small positive value, indicating that the planes of the involved atoms are nearly parallel.

• In a trans-peptide bond, this angle is close to 180 degrees, which is more stable.

✅ Correct Answer: 1. 0

The cis-peptide bond has an O-C-N-H dihedral angle of approximately 0 degrees. This means the two planes formed by the atoms involved in the peptide bond are nearly parallel to each other in the cis configuration. The trans configuration typically corresponds to an angle close to 180 degrees, which is the more common and energetically stable form.