# DBT JRF 2022 — Question 15

Exam: DBT JRF 2022 · Section: B · Topic: Biochemistry › Protein Structure - Peptide Bond Conformation · Difficulty: Medium

## Question

Amide bonds between two amino acids (as shown below) are generally in trans-conformation. The atoms are labeled as A1 through A6. The angle measured for defining the trans-conformation of the amide bond is the angle between: ![figure](https://res.cloudinary.com/dxil5euku/image/upload/v1779453123/pyq/6a104cb5920734408bc0c6d8/DBTJRF22-IMGB15.png)

## Options

- **A.** the atoms A2, A3 and A4.
- **B.** the planes formed by A1,A3,A4 and A3,A4,A6.
- **C.** the planes formed by A2,A3,A4 and A6,A4,A5.
- **D.** the planes formed by A2,A3,A4 and A3,A4,A6.

## Answer

Option D

## Explanation

Omega dihedral angle and trans-conformation of the peptide bond: The peptide bond's conformation is described by the omega ( $\omega$ ) dihedral angle, measured around the C-N bond. Dihedral angle measurement: • The $\omega$ angle is defined by 4 consecutive atoms: $\text{C}\alpha_1 - \text{C} - \text{N} - \text{C}\alpha_2$ • This corresponds to atoms A2-A3-A4-A6 in the labelling of the question. • In practice, it is measured as the angle between the two PLANES: plane(A2,A3,A4) and plane(A3,A4,A6). In the trans-conformation: $\omega = 180°$ (the two Cα atoms are on opposite sides of the peptide bond). ~99.9% of peptide bonds are trans. In the cis-conformation: $\omega = 0°$ (less stable, mostly found before Pro residues — ~5%). Answer: Planes formed by A2,A3,A4 and A3,A4,A6 (Option 4).

Source: https://mypyqbuddy.com/questions/amide-bonds-between-two-amino-acids-as-shown-6a104cd5920734408bc0c71e