93. Which one of the statements relating to properties and structures of two proteins is most
appropriate?
(a) Two proteins with very similar secondary structures will have similar stability,
(b) Two proteins with very similar secondary structures will have similar tertiary structures
(c) Two proteins with very similar tertiary structures will be localized to similar compartments inside
the cell
(d) Two proteins with very simple tertiary structures will have very similar secondary structures

Correct Answer:

(b) Two proteins with very similar secondary structures will have similar tertiary structures

Detailed Explanation:

Proteins have four levels of structure: primary, secondary, tertiary, and quaternary. Understanding how these levels relate helps in predicting a protein’s function and localization.

Let’s break down the options:

• (a) Two proteins with very similar secondary structures will have similar stability
  Incorrect. Stability is influenced by more than just secondary structure—it also depends on interactions in the tertiary structure, disulfide bridges, hydrophobic packing, salt bridges, and environmental conditions like pH and temperature.

• (b) Two proteins with very similar secondary structures will have similar tertiary structures
  Correct. While not always guaranteed, similar secondary structures (like α-helices and β-sheets arranged in the same topology) often lead to similar tertiary structures, especially if their folding patterns are conserved. Structural similarity often reflects evolutionary conservation and may imply a shared function or origin.

• (c) Two proteins with very similar tertiary structures will be localized to similar compartments inside the cell
  Incorrect. Localization depends on signal sequences and post-translational modifications, not just structure. Two proteins may have similar structures but function in different compartments.

• (d) Two proteins with very simple tertiary structures will have very similar secondary structures
  Incorrect. Simple tertiary structures don’t necessarily imply similar secondary structures. Secondary structure refers to local folding patterns, which can differ even in simple proteins.

Summary:

While secondary structure refers to local conformations (like helices and sheets), tertiary structure is about the overall 3D folding. If two proteins share very similar secondary structures, it’s a good indicator—but not a guarantee—that their overall fold (tertiary structure) might be similar. That’s why option (b) is the most appropriate choice in the context of structural biology.