3.3.1 Temperature

Introduction

Temperature is one of the most important factors affecting the rate of enzyme action. Enzymes are proteins, and their activity is highly sensitive to temperature changes. Understanding how temperature affects enzyme activity is essential for understanding enzyme function in living organisms and in industrial applications.

Definition

Optimum Temperature: The temperature that promotes maximum activity is called an optimum temperature.

In simple words: Optimum temperature is the temperature at which an enzyme works best.

Core Concept

• Heating increases molecular motion.
• The molecules of the substrate and enzyme move more quickly.
• The probability of a reaction to occur is increased.
• Increasing temperature affects the rate of reaction:
• An increase of just 10°C in the existing temperature doubles the rate of reaction.
• But this effect remains up to a certain limit.
• Optimum Temperature: The temperature that promotes maximum activity.
• Maximum Temperature: The temperature which causes denaturation of enzyme.
• Minimum Temperature: The temperature where an inactive enzyme becomes active again.

Detailed Explanation

Effect of Temperature on Enzyme Activity

1. Increasing Temperature (Up to Optimum):

• Heating increases molecular motion.
• Substrate and enzyme molecules move more quickly.
• More collisions occur between enzyme and substrate.
• The probability of a reaction increases.
• The rate of reaction increases.
• For every 10°C rise in temperature, the rate of reaction doubles (Q10 effect).

2. At Optimum Temperature:

• The rate of reaction is at its maximum.
• The enzyme works most efficiently.
• The active site is perfectly shaped for the substrate.
• The rate of reaction is highest.

3. Above Optimum Temperature:

• A decrease in the rate of reaction occurs.
• Despite the increasing frequencies of collision, the rate decreases.
• This is because the secondary and tertiary structures of the enzyme have been disrupted.
• The enzyme is said to be denatured.
• The enzyme unfolds.
• The precise structure of the active site is gradually lost.
• The substrate can no longer bind to the active site.
• The reaction stops.

4. Low Temperature (Below Optimum):

• If temperature is reduced to near or below freezing point, enzymes are inactivated, not denatured.
• They will regain their catalytic influence when higher temperatures are restored.
• This temperature where an inactive enzyme becomes active again is called minimum temperature.

Temperature Range for Enzyme Activity

Denaturation

Definition: Denaturation is the loss of the three-dimensional structure of a protein, leading to loss of function.

• Caused by high temperature.
• Hydrogen bonds, ionic bonds, and hydrophobic interactions are disrupted.
• The enzyme unfolds.
• The active site is destroyed.
• The enzyme can no longer bind to the substrate.
• Denaturation is usually irreversible.

Bonds Affected: - The bonds which are most sensitive to temperature change are hydrogen bonds.

Examples of Optimum Temperature

• All human enzymes have an optimum temperature of about 37–38°C.
• This is the normal body temperature.
• At this temperature, enzymes work most efficiently.
• Above this temperature, enzymes begin to denature.
• Below this temperature, enzymes are less active.

• Bacteria living in hot springs may have an optimum temperature of 70°C or higher.
• Such enzymes have been used in biological washing powders for high-temperature washes.
• These enzymes are called thermophilic enzymes or thermozymes.
• They are stable at high temperatures.

Graph of Temperature vs. Rate of Reaction

Key Features:

• Bell-shaped curve.
• Rising phase: increasing temperature increases rate.
• Peak: optimum temperature.
• Falling phase: decreasing rate due to denaturation.

Q10 (Temperature Coefficient)

Definition: Q10 is the factor by which the rate of a reaction increases for every 10°C rise in temperature.

• For most enzymes, Q10 is 2–3.
• This means the rate doubles or triples for every 10°C rise.

• If the rate at 20°C is 10 units, at 30°C it will be 20–30 units.
• This holds true up to the optimum temperature.

Applications of Temperature Effects

Science Tidbits (from textbook)

• All human enzymes have an optimum temperature of about 37–38°C.
• Bacteria living in hot springs may have an optimum temperature of 70°C or higher.
• Such enzymes have been used in biological washing powders for high-temperature washes.
• If temperature is reduced to near or below freezing point, enzymes are inactivated, not denatured.
• They will regain their catalytic influence when higher temperatures are restored.
• This temperature where an inactive enzyme becomes active again is called minimum temperature.

Intermediate Level

Temperature Effects in Detail

Denaturation vs. Inactivation

Graph Analysis

Comparison of Human and Thermophilic Enzymes

Important Points

• 1. Heating increases molecular motion.
• 2. Thus the molecules of the substrate and enzyme move more quickly, so probability of a reaction to occur is increased.
• 3. Increasing temperature affects the rate of reaction in such a way that an increase of just 10°C in the existing temperature doubles the rate of reaction but this effect remains up to a certain limit.
• 4. The temperature that promotes maximum activity is called an optimum temperature.
• 5. If the temperature is increased above this level, then a decrease in the rate of the reaction occurs despite the increasing frequencies of collision.
• 6. This is because the secondary and tertiary structures of the enzyme have been disrupted and the enzyme is said to be denatured.
• 7. The enzyme unfolds and the precise structure of the active site is gradually lost.
• 8. This temperature which causes denaturation of enzyme is called maximum temperature.
• 9. The bonds which are most sensitive to temperature change are hydrogen bonds.
• 10. All human enzymes have an optimum temperature of about 37–38°C.
• 11. Bacteria living in hot springs may have an optimum temperature of 70°C or higher.
• 12. Such enzymes have been used in biological washing powders for high-temperature washes.
• 13. If temperature is reduced to near or below freezing point, enzymes are inactivated, not denatured.
• 14. They will regain their catalytic influence when higher temperatures are restored.
• 15. This temperature where an inactive enzyme becomes active again is called minimum temperature.

Remember

• - Temperature = increases rate up to optimum; denaturation above; inactivation below
• - Optimum temperature = maximum activity
• - Maximum temperature = denaturation
• - Minimum temperature = inactivation (reversible)
• - **Human enzymes** = 37–38°C
• - Thermophilic bacteria = 70°C or higher
• - Q10 = rate doubles for every 10°C rise
• - Hydrogen bonds = most sensitive to temperature
• - Denaturation = irreversible loss of structure and function
• - Inactivation = reversible loss of activity at low temperature

Common Mistakes

• 1. Thinking enzymes are denatured at low temperature – Enzymes are inactivated at low temperature, not denatured.
• 2. Confusing optimum temperature and maximum temperature – Optimum = maximum activity; Maximum = denaturation.
• 3. Thinking denaturation is reversible – Denaturation is usually irreversible.
• 4. Thinking all enzymes have the same optimum temperature – Different enzymes have different optimum temperatures.
• 5. Forgetting the Q10 effect – Rate doubles for every 10°C rise (up to optimum).
• 6. Thinking temperature only affects the substrate – Temperature affects the enzyme's structure as well.
• 7. Confusing inactivation and denaturation – Inactivation = reversible; Denaturation = irreversible.
• 8. Thinking human enzymes work best at 70°C – Human enzymes work best at 37–38°C.
• 9. Thinking thermophilic enzymes work at low temperatures – Thermophilic enzymes work at high temperatures.
• 10. Forgetting the role of hydrogen bonds – Hydrogen bonds are most sensitive to temperature changes.
• 11. Thinking enzymes can work at any temperature – Enzymes have a specific temperature range.
• 12. Confusing the graph shape – The graph is a bell-shaped curve (rising, peak, falling).

Quick Revision

• Heating increases molecular motion.
• Thus the molecules of the substrate and enzyme move more quickly, so probability of a reaction to occur is increased.
• Increasing temperature affect the rate of reaction in such a way that an increase of just 10°C in the existing temperature doubles the rate of reaction but this effect remains up to a certain limit.
• The temperature that promotes maximum activity is called an optimum temperature.
• If the temperature is increased above this level, then a decrease in the rate of the reaction occurs despite the increasing frequencies of collision.
• This is because the secondary and tertiary structures of the enzyme have been disrupted and the enzyme is said to be Denatured.
• The enzyme unfolds and the precise structure of the active site is gradually lost.
• This temperature which causes denaturation of enzyme is called maximum temperature.
• The bonds which are most sensitive to temperature change are hydrogen bonds.
• All human enzymes have an optimum temperature of about 37–38°C, but bacteria living in hot springs may have an optimum temperature of 70°C or higher.
• Such enzymes have been used in biological washing powders for high temperature washes.
• If temperature is reduced to near or below freezing point, enzymes are inactivated, not denatured.
• They will regain their catalytic influence when higher temperatures are restored.
• This temperature where an inactive enzyme becomes active again is called minimum temperature.

60-Second Revision

• Temperature = increases rate up to optimum; denaturation above; inactivation below
• Optimum temperature = maximum activity
• Maximum temperature = denaturation
• Minimum temperature = inactivation (reversible)
• **Human enzymes** = 37–38°C
• Thermophilic bacteria = 70°C or higher
• Q10 = rate doubles for every 10°C rise
• Hydrogen bonds = most sensitive to temperature
• Denaturation = irreversible loss of structure and function
• Inactivation = reversible loss of activity at low temperature
• Warning: Enzymes are inactivated at low temperature, not denatured. Optimum temperature = maximum activity; Maximum temperature = denaturation. Denaturation is usually irreversible. Human enzymes = 37–38°C. Thermophilic enzymes = 70°C or higher. Hydrogen bonds are most sensitive to temperature. The graph is a bell-shaped curve.