Q61.Given below are two statements:
Statement I:
Myoglobin and haemoglobin are oligomeric proteins.
Statement II:
Myoglobin and haemoglobin are heme-containing proteins.
In the light of the above statements, choose the most appropriate answer from the options given below:
(1) Both Statement I and Statement II are correct
(2) Both Statement I and Statement II are incorrect
(3) Statement I is correct but Statement II is incorrect
(4) Statement I is incorrect but Statement II is correct
Statement I is incorrect while Statement II is correct, so option (4) is the answer. Myoglobin is monomeric (single chain), not oligomeric, whereas hemoglobin is tetrameric (four chains). Both contain heme groups for oxygen binding.
Protein Structures
Myoglobin functions as a monomeric globular protein with one polypeptide chain and a single heme prosthetic group for oxygen storage in muscles. Hemoglobin, however, is an oligomeric tetramer (two α and two β subunits), enabling cooperative oxygen binding and transport. The heme group is present in both, binding Fe²⁺ reversibly to O₂.
Option Analysis
-
Option 1: Incorrect—Statement I wrongly groups myoglobin as oligomeric.
-
Option 2: Incorrect—Statement II correctly identifies both as heme proteins.
-
Option 3: Incorrect—Statement I false; myoglobin lacks multiple subunits.
-
Option 4: Correct—myoglobin monomeric, both heme-containing.
Introduction to Myoglobin Haemoglobin Oligomeric Proteins Heme-Containing
Myoglobin haemoglobin oligomeric proteins heme-containing tests protein classification in exams like NEET. Statement I claims both are oligomeric; Statement II says both contain heme. This guide verifies structures, evaluates options, and clarifies differences for biology students.
Myoglobin Structure and Function
Myoglobin is a monomeric protein (single 153-amino-acid chain) with 75% α-helices forming a globular fold around one heme group. It stores oxygen in muscle cells, showing hyperbolic O₂-binding due to non-cooperative binding. Unlike hemoglobin, it lacks quaternary structure.
Haemoglobin Structure and Function
Haemoglobin is an oligomeric tetramer (α₂β₂, ~64 kDa) where subunits interact for cooperative O₂ binding, yielding a sigmoidal curve. Each subunit has a heme prosthetic group; conformational shifts (T to R state) enhance O₂ delivery from lungs to tissues.
Evaluating the Statements
Statement I incorrect: myoglobin monomeric, haemoglobin oligomeric. Statement II correct: both bind O₂ via heme iron (Fe²⁺). Option (4) fits perfectly.
Exam Options Breakdown
Biological Significance
These differences enable specialization: myoglobin stores O₂ locally, haemoglobin transports systemically. Understanding myoglobin haemoglobin oligomeric proteins heme-containing aids exam prep and biochemistry insights.
