The correct answer is (2) B is obtained with protein with positive cooperativity.
Introduction
The analysis of ligand binding isotherms provides insight into protein-ligand interactions, stoichiometry, and cooperative behavior in molecular biology and biochemistry. Classical binding curves distinguish between monomeric proteins exhibiting simple binding and oligomeric proteins displaying cooperative binding. This article explores the meaning of two distinct binding profiles in terms of cooperativity and protein structure.
Understanding the Binding Isotherms
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Curve A (straight line):
Represents non-cooperative binding, typically seen with monomeric proteins or proteins with a single binding site. Ligand binding increases linearly with available binding protein and is described by simple, hyperbolic (Michaelis-Menten-like) kinetics. -
Curve B (sigmoidal curve):
Indicates positive cooperativity, found in oligomeric proteins with multiple ligand-binding sites (e.g., hemoglobin). The binding of one ligand increases the affinity of the protein for additional ligand molecules, resulting in a sigmoidal isotherm.
Statement Analysis
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Option (1): A is oligomeric, B is monomeric
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Incorrect. Monomeric proteins usually yield curve A, not B. Oligomeric proteins with cooperativity yield curve B.
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Option (2): B is protein with positive cooperativity
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Correct. The sigmoidal shape in curve B is the hallmark of positive cooperative binding, often described by the Hill equation.
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Option (3): A and B are same protein at different temperatures
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Not correct. Temperature can influence binding but does not convert a hyperbolic into a sigmoidal curve solely due to temperature change.
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Option (4): Profile B not possible
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Incorrect. Sigmoidal curves are classical evidence for cooperative binding.
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Molecular Basis of Positive Cooperativity
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Positive cooperativity occurs in proteins with multiple subunits.
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Allosteric interactions between subunits mean that binding of the first ligand increases the probability of subsequent ligand binding.
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Examples include oxygen binding to hemoglobin.
Summary Table
| Curve | Shape | Protein Type | Cooperativity | Example |
|---|---|---|---|---|
| A | Linear | Monomeric | None (1:1 binding) | Myoglobin, typical enzyme |
| B | Sigmoidal | Oligomeric | Positive cooperativity | Hemoglobin, multi-subunit proteins |
Conclusion
Curve B in the binding isotherm demonstrates positive cooperativity, which is characteristic of oligomeric proteins containing multiple ligand-binding sites capable of allosteric regulation. Hence, option (2) correctly identifies the molecular mechanism behind the observed binding behavior.
29 Comments
Khushi Vaishnav
September 12, 2025B is obtained with protein with positive cooperativity
Varsha Tatla
September 13, 2025Bis protein with positive cooperativity bcz binding of one mol facilitate the 2nd next molecule binding and thus sigmoidal curve obtained
Kanica Sunwalka
September 13, 2025B is obtained with protein with + ve cooperativity
(Sigmoid curve = Hill rxn )
Aakansha sharma Sharma
September 13, 2025The correct answer is (2) B is obtained with protein with positive cooperativity.
Kajal
September 14, 2025Option 2 is correct as B showing positive cooperation found in oligomeric protein with multiple ligand binding sites
Pratibha Jain
September 14, 2025correct answer is option (2) B is obtained with protein with positive cooperativity.
Rishita
September 14, 2025B is the correct answer
Mohd juber Ali
September 14, 2025Curv A straight line (hyperbolic) monomeric protein
Curv B sigmoid curv oligomeric protein
Tmp does not effect the curve from hyperbolic to sigmoid only influence binding
CurvB is +co opretive
Option B is right
Aafreen Khan
September 14, 2025B is obtained with protein with positive cooperativity ( sigmoid curve – Hill reaction)
Anju
September 14, 2025Ans:2
The sigmoid curve shows the +ve cooperation
Santosh Saini
September 14, 2025Sigmoidal curve show positive cooperativity with oligomeric protein bcz oligomeric protein have multiple binding site where the binding of one ligand molecules increase the protein affinity
Dharmpal Swami
September 14, 2025Curve B is represent positive cooperativity and found in oligomeric protein
Pooja
September 14, 2025B is obtained with protein with positive cooperativity
Soniya Shekhawat
September 14, 2025Temperature can influence binding but does not convert a hyperbolic into a sigmoidal curve solely due to temperature change and only 2nd option is correct which is B protein is from positive cooperation.
yashika
September 14, 2025Linear monomeric
Vanshika Sharma
September 14, 2025Curve b represent the positive cooperativity
Muskan singodiya
September 14, 2025B is obtained with protein with positive cooperative
Kirti Agarwal
September 14, 2025Shape in curve B is the hallmark of positive cooperation
Opt b is correct
Pallavi Ghangas
September 14, 2025Straight line curve shows monomeric protein and sigmoid shows positive cooprativity
Palak Sharma
September 14, 2025Curve B (sigmoidal curve): as seen in hill’s rxn
Indicates positive cooperativity, found in oligomeric proteins with multiple ligand-binding sites (e.g., hemoglobin).
Deepika sheoran
September 15, 2025B is obtained with protein with positive cooperativity.
Ajay Sharma
September 15, 2025Isotherms means temp is same , a shows monomeric protein binding hence is incorrect and b shows oligomeric binding and positive cooperation hence is correct and a is showing non coperativity
Nilofar Khan
September 15, 2025Curve A (straight line)= monomaric protein and non cooperative binding
Curve B(sygmoid)= oligomaric protein and positive cooperation= hill’ s rex
Correct answer is (b)
B is obtained with protein with positive cooperativity.
Tanvi Panwar
September 15, 2025B is sigmoidal representing positive cooperativity with multiple substrate binding sites.
Khushi Agarwal
September 16, 2025The correct answer is (2) B is obtained with protein with positive cooperativity
Avni
September 16, 2025The correct answer is (2) B is obtained with protein with positive cooperativity.
Priti khandal
September 17, 2025Be is correct sigmoid curve
Muskan Yadav
September 18, 2025B is obtained with protein with positive cooperativity.
Minal Sethi
September 19, 2025B is obtained by positive cooperativity