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Chemistry Question 50 – NEET-UG 2026

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The correct statement about peptides and proteins is

Recall the four levels of protein structure: primary, secondary, tertiary, and quaternary, and the types of bonds involved in each.

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Ninja Strategy•Identify Definitional Errors and Absolutes

Quickly eliminate options that contain absolute terms like 'only' or provide incorrect definitions for fundamental protein structures (e.g., tertiary vs. quaternary, right-handed vs. left-handed helices).

Step 1: Understand Protein Structure Levels✦ Active

Proteins exhibit four levels of structure: primary (amino acid sequence), secondary (α-helix and β-pleated sheet formed by hydrogen bonds), tertiary (overall 3D folding of a single polypeptide chain), and quaternary (arrangement of multiple polypeptide subunits).

💡 Teacher's Secret Hint

Remember that hydrogen bonds are crucial for secondary structures, while various interactions (ionic, hydrophobic, disulfide, H-bonds) stabilize tertiary structure.

Step 2: Analyze Secondary Structures and Bonding○ Expand

The α-helix is a right-handed coiled structure stabilized by intramolecular hydrogen bonds between the carbonyl oxygen of one amino acid and the amide hydrogen of an amino acid four residues away. β-pleated sheets are formed by hydrogen bonds between adjacent polypeptide chains (intermolecular) or segments of the same chain (intramolecular), creating a pleated, sheet-like structure.

💡 Teacher's Secret Hint

Distinguish between intramolecular (within one molecule/chain) and intermolecular (between different molecules/chains) bonds.

Step 3: Evaluate the Given Options○ Expand

Option (1) is incorrect because tertiary structure refers to a single polypeptide chain's 3D folding; quaternary structure involves multiple subunits. Option (2) is incorrect as many proteins are biologically active with only tertiary structure (e.g., myoglobin). Option (4) is incorrect because α-helices are typically right-handed. Option (3) correctly states that β-pleated sheets are held together by hydrogen bonds, which can be intermolecular when multiple chains or distant segments interact.

💡 Teacher's Secret Hint

Pay close attention to specific details like 'two or more subunits', 'only', 'left-handed', and 'intermolecular' vs 'intramolecular'.

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