Enzyme Structure and Function
- Enzyme function is intricately tied to the structure of the active site, enzyme-substrate specificity, and how environmental factors affect the enzyme.
- Their unique three-dimensional structure of enzymes allows them to interact with specific molecules, called substrates, at a region known as the active site.
The Active Site: A Precision-Engineered Region
Definition
Active site
The active site is a small region on an enzyme where the substrate binds. It is formed by a specific sequence of amino acids within the enzyme's overall three-dimensional structure.
Its structure is highly specific, determined by the enzyme’s amino acid sequence and three-dimensional folding.
Key Features of the Active Site
- Shape Complementarity: The active site’s shape matches the substrate, allowing them to fit together.
- Chemical Compatibility: The active site contains amino acids with specific chemical properties (e.g., charge, hydrophobicity) that interact with the substrate.
- Only a few amino acids in the active site are directly involved in catalysis.
- These amino acids are often brought together by the enzyme’s folding, even if they are far apart in the linear sequence.
Enzyme-Substrate Specificity: The Lock-and-Key and Induced-Fit Models
- Enzymes are highly specific, meaning they catalyse only one reaction or a group of closely related reactions.
- This specificity arises from the precise interactions between the enzyme and its substrate.
- This specificity ensures that the enzyme catalyzes only the desired reaction and does not interact with other molecules that do not fit properly into the active site.
The enzyme amylase is specific to the substrate starch, and it catalyzes the hydrolysis of starch into simpler sugars.
Denaturation Disrupts Protein Structure
Definition
Denaturation
Denaturation is the process by which the three-dimensional structure of an enzyme is altered, leading to the loss of its function.
Enzymes rely on their three-dimensional structure to function.Note
- Students often confuse denaturation with the destruction of the enzyme’s primary structure (amino acid sequence).
- Denaturation affects the enzyme’s three-dimensional shape, not its sequence.
Causes of Denaturation
- Temperature: High temperatures break the weak bonds (e.g., hydrogen bonds) that maintain the enzyme’s shape.
- pH Changes: Extreme pH levels disrupt ionic bonds and alter the charge of amino acids, affecting the active site’s structure.
- Chemical Agents: Some chemicals (e.g., heavy metals) can interfere with the bonds stabilizing the enzyme’s structure.
- Denaturation is often irreversible.
- Once the enzyme’s structure is disrupted, it cannot return to its original functional form.
Effects of Denaturation on Enzyme Function
- Loss of Active Site Shape: The substrate can no longer bind, preventing the enzyme from catalysing the reaction.
- Reduced Catalytic Efficiency: Even if binding occurs, the enzyme may not be able to lower the activation energy effectively.
In industrial enzymes used for laundry detergents, if the enzyme is exposed to extreme heat during washing, it can denature and lose its ability to break down stains, making it ineffective.
Theory of Knowledge- How does the concept of enzyme specificity relate to the broader idea of structure determining function in biology?
- Can you think of other examples where this principle applies?
- What is the role of the active site in enzyme catalysis?
- How does the induced-fit model differ from the lock-and-key model?
- What are three factors that can cause enzyme denaturation?
- Why is enzyme–substrate specificity important for metabolic regulation?
