Describe enzyme action: active site shape is complementary to its substrate and product formation.

What is an Enzyme?

Enzymes are biological catalysts that speed up chemical reactions in the body. Think of them as super‑fast chefs that help food (substrates) turn into dishes (products) without being used up.

Active Site: The Keyhole

The active site is a special pocket on the enzyme where the substrate fits perfectly, just like a lock and key or a glove for a hand 🧤. The shape, charge and chemical properties of the active site are complementary to the substrate.

Enzyme Action: The Reaction Cycle

1. Substrate (S) binds to the enzyme (E) forming the enzyme‑substrate complex (ES).
   $E + S \rightarrow ES$
2. The complex changes shape slightly (induced fit) to help the reaction happen.
3. Product (P) is released, and the enzyme is ready for another round.
   $ES \rightarrow E + P$

In one line: $$E + S \leftrightarrow ES \rightarrow E + P$$

Exam Tip: Remember the “Lock & Key” and “Induced Fit” models.

When answering questions, mention:

• Active site shape is complementary to the substrate.
• Binding forms an ES complex.
• Product is released, enzyme unchanged.
• Use the equation $E + S \leftrightarrow ES \rightarrow E + P$.

Example: Amylase Breaking Down Starch

Amylase (E) in saliva targets starch (S). The active site fits the starch chain, cleaving it into maltose (P). The enzyme is free to bind more starch, just like a chef chopping more potatoes.

Quick Quiz

1. What does the active site look like compared to its substrate?
2. Write the overall reaction equation for an enzyme-catalysed reaction.
3. Give an example of an enzyme and its substrate.