Quarternary structure of protein is

Options

A. arrangement of amino acids in polypeptide chain
B. inter-relationship of amino in a polypeptide chain
C. inter-relation between polypeptide chains of a protein having more than two polypeptide chains
D. all of the above

Answer

**Step-by-Step Solution:**

1. **Understanding Protein Structure Levels:**
- Proteins have four levels of structure: primary, secondary, tertiary, and quaternary.
- The primary structure refers to the linear sequence of amino acids in a polypeptide chain.

2. **Defining Secondary and Tertiary Structures:**
- The secondary structure involves the folding or coiling of the polypeptide chain into structures such as alpha helices and beta sheets.
- The tertiary structure is the overall three-dimensional shape of a single polypeptide chain, which results from interactions among various side chains (R groups) of the amino acids.

3. **Introducing Quaternary Structure:**
- The quaternary structure refers to the assembly of multiple polypeptide chains (subunits) into a larger functional protein complex.
- These subunits can be arranged in various ways, such as linear, plate-like, or cube-like formations.

4. **Example of Quaternary Structure:**
- A classic example of quaternary structure is hemoglobin, which consists of four subunits: two alpha and two beta chains. The arrangement of these subunits allows hemoglobin to function effectively in transporting oxygen in the blood.

5. **Conclusion:**
- The quaternary structure of a protein is defined by the interrelationship and arrangement of multiple polypeptide chains or subunits, distinguishing it from the other levels of protein structure.

**Final Answer:**
The quaternary structure of a protein is the arrangement and interaction of multiple polypeptide chains (subunits) into a larger functional complex, such as hemoglobin.

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