Question

Select a conjugated protein

• A. Collagen
• B. Albumin
• C. Keratin
• D. Hemoglobin

Hint:

• Simple proteins: Yield only amino acids upon hydrolysis.
• Conjugated proteins: Yield amino acids + a non-protein prosthetic group.
• Hemoglobin's prosthetic group is heme (an iron-containing porphyrin).

Answer 1

The Correct Option is D

Proteins can be classified based on their composition:

• Simple Proteins: On hydrolysis, yield only amino acids or their derivatives. Examples: Albumins, Globulins, Glutelins, Prolamins, Scleroproteins (like collagen, keratin, elastin).
• Conjugated Proteins: Proteins that are combined with a non-protein component, called a prosthetic group. On hydrolysis, they yield amino acids plus the prosthetic group. Examples:
  • Nucleoproteins: Protein + Nucleic acid (e.g., ribosomes, viruses).
  • Glycoproteins: Protein + Carbohydrate (e.g., mucin, some antibodies).
  • Lipoproteins: Protein + Lipid (e.g., chylomicrons, LDL, HDL).
  • Phosphoproteins: Protein + Phosphate group (e.g., casein in milk).
  • Chromoproteins (Metalloproteins): Protein + Pigment or Metal ion (e.g., Hemoglobin - contains heme group with iron; Chlorophyll-protein complexes).

Let's analyze the options: (a) Collagen: A fibrous simple protein (scleroprotein), a major component of connective tissue. (b) Albumin: A globular simple protein found in blood plasma and egg white. (c) Keratin: A fibrous simple protein (scleroprotein) found in hair, nails, skin. (d) Hemoglobin: A chromoprotein (specifically a metalloprotein) found in red blood cells. It consists of a protein part (globin) and a non-protein prosthetic group (heme), which contains an iron atom. The heme group is responsible for oxygen binding. Thus, hemoglobin is a conjugated protein. \[ \boxed{\text{Hemoglobin}} \]