Biological Molecules » Temperature Effects on Enzymes

What you'll learn this session

Study time: 30 minutes

How temperature affects enzyme activity
The optimum temperature for enzymes
Why enzymes denature at high temperatures
How cold temperatures affect enzyme function
Real-world applications of enzyme temperature relationships

Introduction to Temperature Effects on Enzymes

Enzymes are biological catalysts that speed up chemical reactions in living organisms. Without enzymes, these reactions would happen too slowly to support life. But enzymes are sensitive to their environment, especially temperature. Let's explore how temperature affects these vital proteins and why this matters for living organisms.

Key Definitions:

Enzyme: A protein molecule that acts as a biological catalyst, speeding up chemical reactions without being used up.
Substrate: The molecule that an enzyme acts upon.
Active site: The region of an enzyme where the substrate binds.
Denaturation: The process where proteins lose their structure due to external stress like high temperature.
Optimum temperature: The temperature at which an enzyme works most efficiently.

🔥 Temperature and Reaction Rate

As temperature increases, molecules move faster and collide more frequently. This means enzyme-substrate collisions happen more often, increasing the rate of reaction. However, this is only true up to a certain point!

🌡 Enzyme Sensitivity

Enzymes are proteins with delicate 3D structures. Their shape is crucial for function. Temperature changes can alter this shape, affecting how well they work.

The Temperature-Enzyme Activity Relationship

The relationship between temperature and enzyme activity follows a bell-shaped curve. This pattern is crucial to understand for your IGCSE exams.

The Enzyme Activity Curve

If we plot enzyme activity against temperature, we see a curve that rises, reaches a peak and then falls sharply. Let's break this down:

🥶 Low Temperatures

At low temperatures (0-10°C), enzymes and substrates have less kinetic energy. They move slowly and collide less frequently. This results in a slow reaction rate.

👍 Optimum Temperature

As temperature increases, reaction rate increases until it reaches the optimum temperature. For human enzymes, this is typically around 37°C (body temperature).

🔥 High Temperatures

Above the optimum, the enzyme's protein structure begins to break down (denature). The active site changes shape and can no longer bind to the substrate.

Why Enzymes Denature

Denaturation is a key concept in understanding enzyme function. When an enzyme denatures, it loses its 3D shape and can no longer function properly.

📈 The Science of Denaturation

Enzymes are held in their specific 3D shape by weak bonds (hydrogen bonds, ionic bonds and hydrophobic interactions). High temperatures provide enough energy to break these bonds. When these bonds break, the enzyme unravels and loses its specific shape.

💡 Key Point to Remember

Denaturation is usually permanent! Once an enzyme has denatured due to high temperature, cooling it down won't restore its function. This is why cooking food permanently changes its texture and why high fevers can be dangerous.

Optimum Temperature for Different Enzymes

Not all enzymes have the same optimum temperature. This varies depending on the organism and the environment it lives in.

🦊 Mammals

Enzymes in humans and other mammals typically work best at around 37°C, which matches our body temperature.

🐟 Cold-Water Fish

Fish living in cold waters have enzymes with lower optimum temperatures, sometimes as low as 5-10°C.

💦 Thermophiles

Some bacteria live in hot springs and have enzymes that function optimally at 70-80°C or even higher!

Case Study Focus: Laundry Detergents

Modern laundry detergents contain enzymes called proteases and lipases that break down protein and fat stains. Scientists have engineered these enzymes to work at higher temperatures (40-60°C) than human enzymes. This allows them to clean clothes effectively in hot water without denaturing. Some newer "bio" detergents contain enzymes that work well in cold water, saving energy!

Cold Temperatures and Enzyme Activity

While we often focus on high temperatures denaturing enzymes, cold temperatures also significantly affect enzyme function.

❄ Effects of Cold

At low temperatures, enzymes don't denature, but they have much less kinetic energy. This means fewer successful collisions between enzymes and substrates. The reaction still happens, but much more slowly. This is why food spoils more slowly in the refrigerator than at room temperature.

🧊 Cold Adaptation

Some organisms that live in very cold environments have evolved enzymes with structural modifications that keep them flexible and functional at low temperatures. These "psychrophilic" enzymes have fewer rigid bonds and more flexible active sites.

Practical Applications

Understanding how temperature affects enzymes has many practical applications in everyday life and industry:

Food preservation: Refrigeration slows enzyme activity in food, reducing spoilage.
Cooking: Heat denatures enzymes in food, changing texture and flavour.
Medicine: High fevers can be dangerous because they may denature essential enzymes in the body.
Industrial processes: Enzymes are used in many industries, from cheese-making to biofuel production, where temperature control is crucial.
PCR (Polymerase Chain Reaction): Uses heat-stable enzymes from thermophilic bacteria to replicate DNA at high temperatures.

Exam Tip: Drawing Enzyme-Temperature Graphs

In your IGCSE exam, you might be asked to draw or interpret a graph showing the relationship between temperature and enzyme activity. Remember the characteristic bell-shaped curve: activity increases with temperature up to the optimum, then drops sharply as denaturation occurs. Make sure you can explain what's happening at each stage of the curve!

Summary: Temperature Effects on Enzymes

📖 Key Points to Remember

Enzymes are proteins that catalyse reactions in living organisms
As temperature increases, enzyme activity increases up to an optimum
Beyond the optimum temperature, enzymes denature and lose function
Different enzymes have different optimum temperatures
Cold temperatures slow enzyme activity but don't usually denature enzymes

✅ Check Your Understanding

Can you explain:

Why cooking an egg changes it permanently?
Why refrigeration preserves food?
Why human enzymes work best at 37°C?
How some bacteria can survive in hot springs?

🧠 Test Your Knowledge!