Quaternary structure is present in

Options

A. Histone
B. Haemoglobin
C. Globulin
D. Elastin

Answer

### Step-by-Step Solution:

1. **Understanding Protein Structure**: Proteins have four levels of structure: primary, secondary, tertiary, and quaternary. Each level represents a different aspect of the protein's formation and organization.

2. **Defining Quaternary Structure**: The quaternary structure of a protein refers to the arrangement of multiple polypeptide chains (subunits) that come together to form a functional protein. This structure is stabilized by various interactions, including hydrogen bonds, ionic bonds, and disulfide bridges.

3. **Identifying Examples**:
- **Hemoglobin**: This is a classic example of a protein with quaternary structure. Hemoglobin consists of four polypeptide chains (two alpha and two beta chains) that are linked together. The interaction between these chains is crucial for its function in transporting oxygen in the blood.
- **Histone Proteins**: While histones have a three-dimensional structure, they primarily function in the context of DNA packaging and do not exhibit quaternary structure in the same way hemoglobin does.
- **Globulin and Elastin**: Both of these proteins exhibit tertiary structure but do not have quaternary structure like hemoglobin.

4. **Conclusion**: Based on the information provided, the correct answer to the question "Quaternary structure is present in" is **hemoglobin**.