Enzymes

Enzymes

Enzymes

Made of protein

Present inall living cells Converts substrates

into products

Biological catalysts

Increase the rate of chemical reactions

Remain unchanged by chemical

reaction

ProductSubstrate

Chemical Reactions

A chemical reaction happens when one or more substances is chemically changed into one or more different substances.

A + B C + DChemical reactions take place in cells all the time. These are metabolic reactions. Now some reactions are so slow that they need an enzyme or catalyst to speed them up.

Enzyme

Catalase

Hydrogen peroxide

Water + oxygen

Catalyst

Example

Most metabolic reactions are reversible, this means they can go in either direction.

A + B C + D

Catalysts

A catalyst is a substance which speeds up a chemical reaction, without itself being changed by the reaction.

1. When a catalyst is present, less energy is needed to get the chemical reaction started.

2. When a catalyst is present, the speed of the chemical reaction is faster.

3. Although a catalyst helps a chemical reaction to happen, it is unchanged at the end of the reaction.

Types & Names of Enzymes

Enzymes are named according to the type of substrate (substance) on which they act. The word usually ends with ‘ase’.

Lipase acts on - Lipids Protease acts on – Proteins Lactase acts on - Lactose

• Intracellular enzymes are made inside cells and they work there too.

• Extracellular enzymes are made inside cells but they work outside cells in organs like the mouth, stomach and intestines.

• They are always proteins.

• They are specific in their action.

• They can be used over and over again.

• They are sensitive to temperature.

• They are sensitive to pH.

• They easily destroyed or inactivated by poisons.

Properties of Enzymes

One Enzyme – One Reaction

There are thousands of different enzymes in your body. Why are there so many different enzymes?

Each enzyme has its own unique protein structure and shape called its ACTIVE SITE, which is designed to match or COMPLEMENT its substrate.

Lock & Key Hypothesis

An enzyme only acts on one type of substance, or substrate.

Therefore, the enzyme is said to be SPECIFIC to its one substrate.

The shape of the active site (binding site) of the enzyme, matches the shape of the substrate. Allowing the two molecules to bind during the chemical reaction.

This theory of enzyme action is called the ‘lock-and-key’ hypothesis.

Properties of enzymes

• Optimum conditions are the conditions at which an enzymes works best.

The rate of enzyme controlled reactions may be affected by temperature and pH.

Effect of Temperature

What happens to the activity of an enzyme as the temperature changes?

Movie

Effect of pH on enzymes

When the pH changes beyond the optimal conditions, the shape of the active site of the enzyme alters and the enzyme is denatured.

Effect of pH on enzyme activity

Most enzymes work best at a pH close to neutral (pH7), but there are some exceptions. Pepsin, an enzyme found in the stomach, has an optimum pH of 2.

Pepsin Catalase Trypsin