133. Which of the following corresponds to the amino acid pair having maximum and minimum number of
allowed conformations in the Ramachandran plot?
1. Max: Gly, Min: Pro
2. Max: Pro, Min: Gly
3. Max: Ala, Min: Lys
4. Max: Lys, Min: Ala

Question

Which of the following corresponds to the amino acid pair having the maximum and minimum number of allowed conformations in the Ramachandran plot?

1. Max: Gly, Min: Pro

2. Max: Pro, Min: Gly

3. Max: Ala, Min: Lys

4. Max: Lys, Min: Ala

Detailed Explanation

The Ramachandran plot is a graphical representation of the dihedral angles (phi (ϕ) and psi (ψ)) of amino acid residues in the protein structure. It is used to visualize the allowed and forbidden regions for different types of amino acids, which helps to understand the conformation and folding of proteins.

• Glycine (Gly): Glycine is unique because it has a small side chain (a hydrogen atom), which allows it to adopt a wide range of dihedral angles, providing maximum flexibility in its conformation. Therefore, it has the highest number of allowed conformations on the Ramachandran plot.

• Proline (Pro): Proline, due to its cyclic side chain, is rigid and restricts the range of allowable dihedral angles. As a result, Proline has the fewest allowed conformations, especially in the Ramachandran plot, where it typically occupies a distinct, more limited region.

✅ Correct Answer: 1. Max: Gly, Min: Pro

• Maximum Allowed Conformations: Glycine (Gly), with its small side chain, is highly flexible and has the maximum number of allowed conformations.

• Minimum Allowed Conformations: Proline (Pro), due to its cyclic structure, restricts the flexibility of its peptide bond and has the minimum number of allowed conformations on the plot.

Conclusion

The Ramachandran plot is a useful tool for understanding protein secondary structure. Glycine, with its small side chain, has more conformational freedom, while proline, with its rigid ring structure, is much more constrained.