Primary Structure: Amino Acid Sequence Steps:

• Define primary structure as the linear sequence of amino acids linked by peptide bonds.
• Assess each statement against this definition to identify correct ones.
• Eliminate statements misattributing features of higher structures (secondary, tertiary) to primary.
• Select option matching only the accurate statements (2 and 4).

Why D is correct:

• Option D identifies statements 2 and 4, which accurately describe primary structure as the amino acid sequence and its role in determining higher-level folding, per the central dogma of protein biosynthesis.

Why the others are wrong:

• A includes 1 and 3, which incorrectly link primary structure to 3D folding or non-peptide bonds.
• B includes 1, wrongly associating primary structure with quaternary assembly.
• C omits 2, excluding the core definition of amino acid sequence.

Final answer: D