BIO101 ‒ Topic 5: Enzymes (Nature, Mode of Action, and Factors
Affecting Enzyme Activity)
1. Definition and Nature of Enzymes
Enzymes are biological catalysts that speed up chemical reactions in living organisms
without being consumed in the process. They are mostly proteins, except for some RNA
molecules known as ribozymes.
2. Characteristics of Enzymes
• Highly specific ‒ act on particular substrates. • Speed up reactions by lowering activation
energy. • Work best under optimal temperature and pH conditions. • Remain unchanged
after reactions. • Can be denatured by extreme heat or unsuitable pH. Text Diagram
Description: Picture a lock-and-key mechanism where the enzyme (lock) fits perfectly with
the substrate (key) to form a product.
3. Mechanism of Enzyme Action
The substrate binds to the enzyme s active site forming an enzyme-substrate complex.
The enzyme converts the substrate into products and releases them, ready to catalyze
another reaction. Text Diagram Description: Imagine a substrate fitting into the enzyme s
active site, reacting, and then releasing a new product.
4. Factors Affecting Enzyme Activity
• Temperature ‒ Activity increases with temperature up to an optimum point, after which
enzymes denature. • pH ‒ Each enzyme has an optimum pH; deviation reduces activity. •
Substrate concentration ‒ Activity increases with concentration until all enzyme sites are
occupied. • Enzyme concentration ‒ Higher enzyme concentration increases reaction rate if
substrate is sufficient.
5. Enzyme Inhibition
Enzyme inhibitors reduce or stop enzyme activity. • Competitive inhibitors bind to the
active site, blocking substrates. • Non-competitive inhibitors bind elsewhere, changing
enzyme shape. Text Diagram Description: Visualize an inhibitor molecule blocking the
enzyme s active site, preventing the substrate from entering.
6. Importance of Enzymes in Living Organisms
Affecting Enzyme Activity)
1. Definition and Nature of Enzymes
Enzymes are biological catalysts that speed up chemical reactions in living organisms
without being consumed in the process. They are mostly proteins, except for some RNA
molecules known as ribozymes.
2. Characteristics of Enzymes
• Highly specific ‒ act on particular substrates. • Speed up reactions by lowering activation
energy. • Work best under optimal temperature and pH conditions. • Remain unchanged
after reactions. • Can be denatured by extreme heat or unsuitable pH. Text Diagram
Description: Picture a lock-and-key mechanism where the enzyme (lock) fits perfectly with
the substrate (key) to form a product.
3. Mechanism of Enzyme Action
The substrate binds to the enzyme s active site forming an enzyme-substrate complex.
The enzyme converts the substrate into products and releases them, ready to catalyze
another reaction. Text Diagram Description: Imagine a substrate fitting into the enzyme s
active site, reacting, and then releasing a new product.
4. Factors Affecting Enzyme Activity
• Temperature ‒ Activity increases with temperature up to an optimum point, after which
enzymes denature. • pH ‒ Each enzyme has an optimum pH; deviation reduces activity. •
Substrate concentration ‒ Activity increases with concentration until all enzyme sites are
occupied. • Enzyme concentration ‒ Higher enzyme concentration increases reaction rate if
substrate is sufficient.
5. Enzyme Inhibition
Enzyme inhibitors reduce or stop enzyme activity. • Competitive inhibitors bind to the
active site, blocking substrates. • Non-competitive inhibitors bind elsewhere, changing
enzyme shape. Text Diagram Description: Visualize an inhibitor molecule blocking the
enzyme s active site, preventing the substrate from entering.
6. Importance of Enzymes in Living Organisms
