If the backbone dihedral angles phi (φ) and psi (ψ) for every residue in a protein are known, what global structural feature can be determined?

Introduction:
Backbone dihedral angles phi (φ) and psi (ψ) define the local geometry of each residue. Knowing them for all residues largely specifies the polypeptide backbone conformation, enabling reconstruction of the three-dimensional fold.

Given Data / Assumptions:

• All φ, ψ angles are known for each residue.
• Bond lengths and bond angles are near standard values.
• No consideration of absolute position (translation/rotation) needed to define shape.

Concept / Approach:

With φ, ψ for each residue and standard peptide geometry (including planar peptide bonds), one can sequentially place each backbone atom in 3D space, yielding the protein’s tertiary structure up to overall rigid-body transformations.

Step-by-Step Solution:

Verification / Alternative check:

Backbone reconstruction from φ, ψ is standard in computational modeling; the resulting coordinates align with experimentally determined tertiary folds.

Why Other Options Are Wrong:

Secondary structure is a subset of tertiary structure; quaternary assembly requires inter-subunit information; thermodynamic stability cannot be deduced solely from geometry; primary sequence cannot be inferred from angles.

Common Pitfalls:

Equating backbone reconstruction with side-chain packing accuracy; ignoring cis peptide bonds and proline exceptions.

Final Answer:

Complete tertiary (3D) structure of the polypeptide chain