2.2 | Enzymes – The Catalysts of Life

(How do enzymes speed up biological reactions?)

🌱 Overview:

Enzymes are biological catalysts that speed up chemical reactions in cells by lowering activation energy (the energy required to start a reaction). Without enzymes, most life-sustaining reactions would be too slow to support life.

🔹 Part 1: What Are Enzymes?

✅ Enzymes are proteins that help speed up reactions by breaking down or building up molecules.
✅ They are not used up in reactions – they can be reused!
✅ Each enzyme is specific to a reaction, like a key fitting into a lock.

Examples of Enzymes in Biology:

  • Amylase – Breaks down starch into sugar in the mouth.

  • Lipase – Breaks down fats in the intestines.

  • DNA Polymerase – Helps build DNA strands.

🔹 Part 2: How Do Enzymes Work?

1⃣ The Active Site & Substrate

  • Active Site – The specific part of the enzyme where a molecule (substrate) binds.

  • Substrate – The reactant that binds to the enzyme.

  • Enzyme-Substrate Complex – When the enzyme binds to the substrate, it undergoes a temporary change.

2⃣ The Induced Fit Model (Better than Lock & Key!)

  • The enzyme slightly changes shape to fit the substrate perfectly.

  • This reduces activation energy, making the reaction faster.

✅ Think of a handshake: Your hand adjusts slightly to fit someone else’s. That’s how enzymes work!

🔹 Part 3: Factors Affecting Enzyme Activity

Enzymes need specific conditions to function properly. If conditions change too much, the enzyme can denature (lose its shape and stop working).

Factor

Effect

Temperature

Too hot = enzyme denatures (loses shape). Too cold = enzyme slows down.

pH Level

Extreme pH levels disrupt enzyme shape. (Example: Stomach enzymes work best at pH 2, but blood enzymes need pH 7.4).

Substrate Concentration

More substrate = faster reaction (until the enzyme is saturated).

Inhibitors

Molecules that slow or stop enzymes.

🔹 Part 4: Enzyme Inhibitors – How to Stop an Enzyme

✅ Competitive Inhibitors – Block the active site so the substrate can’t bind.
✅ Non-Competitive Inhibitors – Bind elsewhere on the enzyme, changing its shape so it no longer works.

🔎 Example:

  • Cyanide is a deadly poison that inhibits enzymes needed for energy production.