Question

Hemoglobin is a

• A. amino acid
• B. biological catalyst
• C. enzyme
• D. protein

Hint:

Hemoglobin is a classic example of a globular transport protein with a quaternary structure.
While all enzymes are proteins, not all proteins are enzymes. Hemoglobin is a protein, but it is not an enzyme because its function is transport, not catalysis.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
This question asks for the biochemical classification of hemoglobin, which is a vital biomolecule found in red blood cells.

Step 2: Key Formula or Approach:
To classify hemoglobin, we must analyze its structural composition:
- Amino acids are the simple monomeric building blocks of proteins.
- Enzymes are biological catalysts that speed up chemical reactions in living organisms.
- Proteins are large biomolecules consisting of one or more long chains of amino acid residues folded into complex three-dimensional structures.
- Hemoglobin is a metalloprotein with a quaternary structure composed of four polypeptide subunits.

Step 3: Detailed Explanation:
Let us examine the structural and functional details of hemoglobin:
1. Polypeptide Chains: Hemoglobin is a globular protein made of four polypeptide chains (subunits): two alpha (\(\alpha\)) chains and two beta (\(\beta\)) chains.
2. Prosthetic Group: Each subunit contains a non-protein prosthetic group called "heme," which consists of an iron ion (\(\text{Fe}^{2+}\)) coordinated in a porphyrin ring.
3. Function: The primary role of hemoglobin is to transport oxygen from the lungs to the body tissues and return carbon dioxide from the tissues back to the lungs. This is a transport function, not a catalytic one.
4. Classification: Since it does not catalyze metabolic chemical reactions, it is not classified as an enzyme or a biological catalyst (ruling out Options B and C). Because it is a large macromolecular polypeptide assembly, it is not a single amino acid (ruling out Option A).
Therefore, hemoglobin is classified as a transport protein.

Step 4: Final Answer
Thus, the correct option is (D).