The correct answer is Option A: A-III, B-IV, C-II, D-I.

Here's a breakdown of the protein structures and their corresponding characteristics:

1. Primary Structure:

The primary structure refers to the linear sequence of amino acids in a polypeptide chain. This sequence is determined by the genetic code and is crucial for the protein's function.

Match: A - III (Polypeptide chain)

2. Secondary Structure:

The secondary structure arises from the hydrogen bonding between amino acids within the polypeptide chain. This results in the formation of regular, repeating patterns such as:

• Alpha-helix: A coiled structure resembling a spring.
• Beta-sheet: A sheet-like structure formed by hydrogen bonding between adjacent polypeptide segments.

Match: B - IV (Alpha helix and $\beta$ sheet)

3. Tertiary Structure:

The tertiary structure describes the three-dimensional shape of a single polypeptide chain. This structure is formed by interactions between various amino acid side chains, including:

• Hydrogen bonds
• Ionic bonds
• Hydrophobic interactions
• Disulfide bonds (formed between cysteine residues)

Match: C - II (Disulphide bonds)

4. Quaternary Structure:

The quaternary structure refers to the arrangement of multiple polypeptide chains (subunits) into a functional protein complex. This structure is stabilized by the same interactions responsible for the tertiary structure.

Match: D - I (Human haemoglobin)

Human haemoglobin is a classic example of a protein with a quaternary structure. It is composed of four polypeptide chains (two alpha and two beta chains), each of which binds to a heme group, enabling oxygen transport.