Lock & Key and Induced Fit Model

What is the active site?

The active site is the area of the enzyme where the reaction with the substrate takes place.

Why is the active site of an enzyme specific?

The active site is specific and unique in shape due to the specific folding and bonding in the tertiary structure of the protein.

Due to this specific active site, enzymes can only attach to substrates complementary in shape.

State the name of the 2 models for enzyme action.

1. Lock and Key model

2. Induced Fit model

Summarise the lock and key hypothesis.

• Hypothesis suggests that the enzyme is like a “lock” and the substrate is a “key” that fits into the enzyme due to the complimentary shape.

• The substrate molecule fits into and binds to an active site within the enzyme to form an enzyme-substrate complex.

• The original lock and key hypothesis suggests that there is an exact fit between the substrate and the active site of the enzyme.

What is an anabolic enzyme?

Anabolic enzymes build larger products from smaller substrate molecules.

What is a catabolic enzyme?

Catabolic enzymes break large substrate molecules into smaller products.

What is an intracellular enzyme?

Enzymes which work inside cells.

What is an extracellular enzyme?

Enzymes which are secreted from cells and used outside of the cell.

Summarise the induced fit hypothesis.

• Hypothesis suggests that the enzyme is like a “glove” and the substrate is a “hand”.

• The empty glove is not exactly complementary in shape to the hand, but when your hand enters, it enables the glove to mould around it to come completely complementary.

• In a similar way, the active site is induced- it changes in shape slightly to fit the substrate molecule perfectly.

• The fact that a substrate can mould the enzyme to its own shape means that several different substrates can react with the same enzyme.

Which model is currently accepted to accurately explain how enzymes work?

Induced fit model.