Which of the following is a conjugated protein ?

Options

A. Keratin
B. Albumin
C. Collagen
D. Haemoglobin

Answer

To determine which of the following is a conjugated protein, we first need to understand what a conjugated protein is.

### Step-by-Step Solution:

1. **Definition of Conjugated Protein**:
- A conjugated protein is a type of protein that requires a non-polypeptide component, known as a prosthetic group, to function properly. This non-polypeptide component can be a metal ion, a vitamin, or another organic molecule.

2. **Understanding Prosthetic Groups**:
- The prosthetic group is essential for the biological activity of the conjugated protein. For example, in hemoglobin, the prosthetic group is the heme group, which contains iron and is crucial for oxygen transport in the blood.

3. **Analyzing the Options**:
- **Option 1: Keratin**:
- Keratin is a fibrous protein found in hair, nails, and skin. It does not require a prosthetic group to function, so it is not a conjugated protein.
- **Option 2: Albumin**:
- Albumin is a globular protein found in egg whites and blood plasma. It serves various functions but does not require a prosthetic group, making it a simple protein, not a conjugated one.
- **Option 3: Collagen**:
- Collagen is another fibrous protein that provides structure to connective tissues. Like keratin, it does not require a prosthetic group and is not classified as a conjugated protein.
- **Option 4: Hemoglobin**:
- Hemoglobin is a complex protein found in red blood cells. It is a conjugated protein because it contains a heme prosthetic group that is essential for its function in oxygen transport.

4. **Conclusion**:
- Based on the analysis of the options, the correct answer is **Hemoglobin**, as it is the only option that qualifies as a conjugated protein due to its requirement for a prosthetic group (heme) to function.

### Final Answer:
**Hemoglobin** is a conjugated protein.