Protein Tertiary Structure Interactions

Steps:

• Identify tertiary structure as the 3D folding of a polypeptide chain stabilized by interactions between R-groups.
• Recall key interactions: hydrogen bonds (1), ionic bonds/salt bridges (2), and hydrophobic effects (3).
• Confirm all three directly stabilize the globular shape in enzymes by minimizing energy.
• Eliminate options excluding any interaction, as all contribute.

Why A is correct:

• Tertiary structure requires all three interactions per biochemistry definitions, ensuring specific enzyme shape for function.

Why the others are wrong:

• B excludes hydrophobic effects, essential for core packing.
• C omits ionic bonds, critical for charged residue stabilization.
• D ignores hydrogen bonds, vital for polar group alignment.

Final answer: A