The Question is from neet-botany biomolecules-biology enzymes, and it was created by the author NISHANTH

Question

An enzyme exhibiting positive cooperativity shows a sigmoidal kinetic curve.  Which statement is FALSE regarding this type of enzyme?

NISHANTH · Accepted Answer

## CORE INFORMATION
✓ **Answer**: A
## CONCEPT FRAMEWORK
 **Primary Concept**: Enzyme kinetics and cooperativity
 **Related Topics**: Michaelis-Menten kinetics, Hill equation, allosteric enzymes
 **Prerequisites**: Understanding of enzyme-substrate binding, reaction rates, and sigmoidal curves.
## SOLUTION PATHWAY
**Given Information**:
  An enzyme exhibits positive cooperativity and a sigmoidal kinetic curve.
**Method & Steps**:
 1. Understanding Positive Cooperativity: Positive cooperativity means that the binding of one substrate molecule increases the enzyme's affinity for subsequent substrate molecules. This leads to a sigmoidal curve instead of the hyperbolic curve seen in Michaelis-Menten kinetics.
  Reasoning: The initial binding of substrate is weak, but subsequent bindings become progressively stronger, leading to a steeper increase in reaction rate at intermediate substrate concentrations.
 2. Analyzing the Options:
  Option A is FALSE because the binding of the first substrate molecule *increases* the enzyme's affinity for subsequent molecules. This is the defining characteristic of positive cooperativity.
  Option B is TRUE.  Cooperative enzymes typically have multiple subunits, allowing for interactions between subunits that influence substrate binding.
  Option C is TRUE. The Hill coefficient ($n_H$) quantifies cooperativity.  A Hill coefficient greater than 1 indicates positive cooperativity.
  Option D is TRUE. The sigmoidal curve shows that the enzyme's activity is much more sensitive to changes in substrate concentration at intermediate concentrations than a Michaelis-Menten enzyme.
 3. Conclusion:
  Result: Option A is the false statement.
  Verification: The definition of positive cooperativity directly contradicts option A.
 ## OPTION ANALYSIS
A ✓: :x:  This statement is false. Positive cooperativity means the binding of the first substrate *increases* the affinity for subsequent substrates.
B :x: ✓ This statement is true. Multi-subunit enzymes allow for cooperative binding.
C :x: ✓ This statement is true. A Hill coefficient > 1 indicates positive cooperativity.  The Hill equation is given by: $v = \frac{V_{max}[S]^n_H}{K_m^n_H + [S]^n_H}$, where $n_H$ is the Hill coefficient.
D :x: ✓ This statement is true.  The sigmoidal curve reflects a greater sensitivity to changes in substrate concentration compared to the hyperbolic Michaelis-Menten curve.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing positive and negative cooperativity: Remember that positive cooperativity enhances binding, while negative cooperativity diminishes it.
  2.Misinterpreting the Hill coefficient: A Hill coefficient of 1 indicates no cooperativity, while values greater than 1 indicate positive cooperativity and values less than 1 indicate negative cooperativity.
 **Quick Tips**:
  1.Visualize the sigmoidal curve:  The shape itself indicates the increased sensitivity to substrate concentration at intermediate levels.
  2.Remember the key characteristic of positive cooperativity:  enhanced binding affinity with increasing substrate binding.

NISHANTH · Answer

The correct Option is "The binding of the first substrate molecule decreases the enzyme's affinity for subsequent substrate molecules."

NISHANTH · Answer

The enzyme likely has multiple subunits.

NISHANTH · Answer

The Hill coefficient is greater than 1.

NISHANTH · Answer

The enzyme's activity is more sensitive to substrate concentration changes compared to enzymes with Michaelis-Menten kinetics.

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