Structural analogy — α-amylose compared to protein secondary structures The polysaccharide α-amylose adopts a helical conformation. To which common protein secondary structure is this most analogous?

Introduction / Context:
α-Amylose is a component of starch consisting of glucose units linked by α(1→4) glycosidic bonds. Its three-dimensional structure is helical, which invites comparison with canonical protein secondary structures. Recognizing this analogy helps relate carbohydrate conformations to familiar protein motifs.

Given Data / Assumptions:

• α(1→4) linkages favor a regular, repeating geometry.
• Helical cavities in amylose can host iodine, forming the characteristic blue complex.
• Protein α-helices are stabilized by intrachain hydrogen bonds between backbone groups.

Concept / Approach:

Although stabilization forces differ (glycosidic torsion preferences and inter-residue interactions in polysaccharides versus backbone H-bonds in proteins), both α-amylose and α-helices exhibit a right-handed helical geometry with repeating pitch and rise per residue, making α-helix the closest structural analogy among the listed choices.

Step-by-Step Solution:

Verification / Alternative check:

The iodine–amylose color reaction relies on helical cavity formation, experimentally supporting helix geometry; structural models of α-helices show similar overall topology.

Why Other Options Are Wrong:

β-sheets are extended, not helical. β-turns are short directional reversals, not long helices. A hydrophobic core is a tertiary packing phenomenon, not a secondary structure. Random coil lacks the periodicity observed in amylose.

Common Pitfalls:

Assuming all polysaccharides are random coils; ignoring that linkage stereochemistry dictates regular conformations.

Final Answer:

α-helices