The Question is from neet-botany , and it was created by the author K SURESH KUMAR

Question

A researcher isolates an enzyme from a thermophilic bacterium and finds that its activity dramatically decreases when incubated at 25°C compared to its optimal temperature of 70°C. This decrease in activity is MOST likely due to:

K SURESH KUMAR · Accepted Answer

## CORE INFORMATION
✓ **Answer**: B
## CONCEPT FRAMEWORK
 **Primary Concept**: Enzyme structure and function; effect of temperature on enzyme activity
 **Related Topics**: Protein folding, denaturation, activation energy, enzyme kinetics
 **Prerequisites**: Understanding of enzyme active sites, protein structure (primary, secondary, tertiary, quaternary), and the relationship between temperature and molecular motion.
## SOLUTION PATHWAY
**Given Information**:
  * Enzyme isolated from a thermophilic bacterium (adapted to high temperatures).
  * Enzyme activity decreases significantly at 25°C compared to 70°C (optimal temperature).
**Method & Steps**:
 1. Analyze the effect of temperature on protein structure.
  Reasoning:  Proteins, including enzymes, maintain their three-dimensional structure through various weak bonds (hydrogen bonds, van der Waals forces, hydrophobic interactions).  Changes in temperature disrupt these bonds.
  Formula/Rule: None directly applicable, but understanding of protein folding principles is crucial.
 2. Consider the impact of temperature change on enzyme activity.
  Working: At lower temperatures (25°C), the decreased kinetic energy of molecules reduces the frequency of enzyme-substrate collisions.  More importantly, the weaker bonds holding the enzyme's tertiary structure (and thus the active site) together are disrupted, leading to a change in the enzyme's shape and a loss of function.  At the optimal temperature (70°C), the enzyme's structure is best suited for binding its substrate and catalyzing the reaction.
  Key Point:  Thermophilic enzymes are adapted to high temperatures; their structures are more stable at those temperatures than at lower ones.
 3. Evaluate the given options.
  Result: Option B correctly identifies the primary reason for the decreased activity: changes in the enzyme's three-dimensional structure, specifically affecting the active site's ability to bind substrate and catalyze the reaction.
  Verification: The other options are incorrect because: A (increased substrate affinity is unlikely at a temperature far from the optimum); C (activation energy is not directly affected by temperature in this context, the enzyme's ability to lower activation energy is affected by its structure); D (there's no evidence to suggest an increase in inhibitor concentration at lower temperatures).
 ## OPTION ANALYSIS
A :x: Increased substrate affinity is generally observed closer to optimal temperatures, not far below.  Lower temperatures would usually reduce the kinetic energy of substrate molecules, decreasing the rate of enzyme-substrate collisions.
B ✓: Correct.  Lower temperatures disrupt the enzyme's three-dimensional structure, altering the active site and reducing its catalytic activity. This is especially true for an enzyme from a thermophilic organism.
C :x:  The activation energy is lowered *by* the enzyme's catalytic action, not affected directly by temperature in this scenario.  The enzyme's ability to lower activation energy is compromised by structural changes at 25°C.
D :x: There is no information supporting a change in inhibitor concentration related to temperature.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing the effects of temperature on reaction rate with the effects of temperature on enzyme structure:  While temperature affects reaction rate, the primary effect here is on enzyme structure.
  2.Assuming that lower temperatures always increase substrate affinity:  While substrate binding can be affected by temperature, it's not the primary cause of the dramatic decrease in activity in this thermophilic enzyme at 25°C.
 **Quick Tips**:
  1.Remember that enzymes are proteins, and their activity is highly dependent on their three-dimensional structure.
  2.Thermophilic enzymes are adapted to high temperatures; their structures are less stable at lower temperatures.

K SURESH KUMAR · Answer

Increased substrate affinity at lower temperatures.

K SURESH KUMAR · Answer

The correct Option is "Changes in the enzyme's three-dimensional structure affecting the active site."

K SURESH KUMAR · Answer

A decrease in the activation energy of the catalyzed reaction.

K SURESH KUMAR · Answer

An increase in the concentration of competitive inhibitors at lower temperatures.

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