How Do Enzymes Work? Lock and Key vs. Induced Fit Models

Leah Strawbridge

24/10/2025

Biology

enzymes. lock and key theory

Subjects

Biology

Biological molecules

Proteins

350

•

24 Oct 2025

•

1 page

How Do Enzymes Work? Lock and Key vs. Induced Fit Models

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Brand: Knowunity

Leah Strawbridge

@leahstrawbridge_kjnx

Enzymes are biological catalysts that play a crucial role in... Show more

# Enzymes

enzymes are large proteins that catalyse (speed up) reactions.
↳ Enzymes are not changed in the reactions they catalyse

# Lock a

Lock and Key Theory of Enzyme Action

The lock and key theory is a fundamental model explaining how enzymes work and why they exhibit specificity for certain substrates. This theory provides insights into the mechanism of enzyme catalysis and the importance of the active site of an enzyme.

Enzymes are biological catalysts, specifically large protein molecules, that speed up chemical reactions without being consumed in the process. They play a vital role in various metabolic processes within living organisms.

The lock and key theory proposes that enzymes have a specific shape, particularly at their active site, which allows them to catalyze only certain reactions. This specificity is crucial for understanding why enzymes are specific to particular substrates.

Definition: The active site of an enzyme is the region where the catalytic reaction occurs. It has a unique three-dimensional shape that complements the shape of its specific substrate.

According to the lock and key theory, the relationship between an enzyme and its substrate is analogous to a lock and key:

The enzyme (the lock) has a specific shape at its active site.
Only a substrate (the key) with a complementary shape can fit into the enzyme's active site.
This specific fit ensures that the enzyme catalyzes only certain reactions.

Example: A common lock and key model example is the enzyme sucrase, which specifically breaks down the sugar sucrose. The active site of sucrase is shaped to fit only sucrose molecules, not other sugars like lactose or maltose.

At the active site, enzymes can perform two main types of reactions:

Breaking down larger molecules into smaller ones (catabolic reactions)
Joining smaller molecules together to form larger ones (anabolic reactions)

Highlight: The formation of an enzyme-substrate complex is a crucial step in enzyme catalysis. This complex forms when the substrate binds to the enzyme's active site, initiating the catalytic process.

After the reaction is complete and the products are released, the enzyme's active site becomes available again. This allows the enzyme to accept another substrate molecule, continuing its catalytic function.

Vocabulary: Enzyme-substrate specificity refers to the ability of an enzyme to selectively catalyze reactions with particular substrates due to the complementary shapes of the enzyme's active site and the substrate.

While the lock and key theory provides a simple explanation for enzyme specificity, it's important to note that more advanced models, such as the induced fit model of enzyme action, have been developed to account for the dynamic nature of enzyme-substrate interactions.

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Subjects

Biology

Biological molecules

Proteins

Biology

24 Oct 2025

350

1 page

How Do Enzymes Work? Lock and Key vs. Induced Fit Models

Leah Strawbridge @leahstrawbridge_kjnx

Enzymes are biological catalysts that play a crucial role in speeding up chemical reactions in living organisms. This summary explores the lock and key theory of enzyme action, explaining how... Show more

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Lock and Key Theory of Enzyme Action

Definition The active site of an enzyme is the region where the catalytic reaction occurs. It has a unique three-dimensional shape that complements the shape of its specific substrate.

According to the lock and key theory, the relationship between an enzyme and its substrate is analogous to a lock and key

The enzyme (the lock) has a specific shape at its active site.
Only a substrate (the key) with a complementary shape can fit into the enzyme's active site.
This specific fit ensures that the enzyme catalyzes only certain reactions.

Example A common lock and key model example is the enzyme sucrase, which specifically breaks down the sugar sucrose. The active site of sucrase is shaped to fit only sucrose molecules, not other sugars like lactose or maltose.

At the active site, enzymes can perform two main types of reactions

Breaking down larger molecules into smaller ones (catabolic reactions)
Joining smaller molecules together to form larger ones (anabolic reactions)

Highlight The formation of an enzyme-substrate complex is a crucial step in enzyme catalysis. This complex forms when the substrate binds to the enzyme's active site, initiating the catalytic process.

Vocabulary Enzyme-substrate specificity refers to the ability of an enzyme to selectively catalyze reactions with particular substrates due to the complementary shapes of the enzyme's active site and the substrate.