Tertiary Structure Forms Globular Proteins

Steps:

• Define protein structure levels: primary is amino acid sequence; secondary involves local folds like helices; tertiary is the full 3D shape from side-chain interactions; quaternary assembles multiple chains.
• Recognize amylase as a single-chain enzyme with a compact, globular form for function.
• Link globular folding to interactions stabilizing the overall 3D conformation.
• Confirm tertiary level matches this global folding process.

Why C is correct:

• Tertiary structure arises from hydrophobic, ionic, and disulfide bonds between distant amino acids, creating the stable, globular 3D shape essential for enzyme activity like in amylase.

Why the others are wrong:

• A: Primary structure is just the linear amino acid sequence, not folding.
• B: Secondary structure forms local patterns like alpha helices, not the overall globular shape.
• D: Quaternary structure involves multiple subunits, but amylase is a single polypeptide.

Final answer: C