# User:Eric Martz/Ramachandran Principle Quiz

The nine-question quiz below is offered to accompany the interactive Tutorial:Ramachandran principle and phi psi angles, which is also available as a Slideshow and a YouTube video.

1. How many bonded atoms are required to constitute a dihedral (torsion) angle, such as phi or psi?

 None 1 2 3 4 5 → The phi dihedral (torsion) angle is defined by (1) the carboxy carbon from the previous amino acid; (2) N in the amino acid containing the phi bond; (3) Cα in the amino acid containing the phi bond; and (4) the carboxy carbon of the amino acid containing the phi bond.

2. The number of phi and psi angles in an isolated amino acid (not in a polypeptide chain) is:

 None 1 2 3 4 5 → The phi angle involves the carboxy carbon of the previous amino acid in a polypeptide chain. The psi angle involves the N of the subsequent amino acid. Therefore an isolated single amino acid has neither phi nor psi angles.

3. The number of atoms held into a geometric plane by a peptide bond is:

 3 4 5 6 7 8 →

Questions below may have more than one correct answer.

4. The peptide bond is unable to rotate because

 It is a covalent bond. It is a non-covalent bond. Rotation would cause clashes. It is a partially double bond.

5. Phi and psi angles directly determine

 Primary structure. Secondary structure. Tertiary structure. Quaternary structure. → See Protein primary, secondary, tertiary and quaternary structure.

6. Alpha helices are compatible with

 All possible phi-psi angle combinations. A limited range of phi-psi angle combinations. A limited range of phi angles with all possible psi angles. A limited range of psi angles with all possible phi angles. → See Ramachandran Plot.

7. Common secondary structures are energetically favored because

 They optimize main-chain hydrogen bonds. They represent all possible conformations. They maximize clashes between atoms. They minimize clashes between atoms.

8. Overlap of van der Waals radii

 Between two non-bonded atoms is called a clash. Between two covalently bonded atoms is called a clash. Occurring between two non-bonded atoms in a molecular model signifies an energetically favorable interaction. Is physically impossible between two non-bonded real atoms.

9. In a Ramachandran plot, the dots cluster

 Where clashes occur. Where clashes do not occur. Where alpha helices occur. Where beta strands occur. Where alpha helices, beta strands, and turns do not occur. Where the phi and psi angles are energetically favorable.

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