What are Enzymes and how do they work?

What is an Enzyme?
Enzymes have an essential role in the reactions in the body from respiration to digestion. Enzymes are globular proteins with a specific tertiary shape.
Enzymes are Biological Catalysts
Substances that increase the rate of reaction without being a reactant are called catalysts. Enzymes are described as biological catalysts because they increase the metabolic rate of reactions in an organism.
Enzymes lower activation energy
Activation energy is the amount of energy required for the reaction to start. Enzymes reduce the activation energy required for the reaction to occur. This means that with an enzyme the reaction can occur at a lower temperature with a greater rate of reaction.
Examples of Enzymes
Enzymes can be intracellular where reactions occur inside the cell or extracellular where reactions occur outside the cell. Some examples of enzymes in your body are:
1) Catalase (Intracellular)
o Catalase breaks hydrogen peroxide down to water and oxygen.
o Hydrogen peroxide is toxic by product and if it builds up it can kill cells.
2) Lactase (extracellular)
o Lactase breaks down lactose into glucose and galactose
o Lactose intolerance can develop in people who are deficient in intestinal enzyme lactase.
How do enzymes work?
Enzymes have an active site which is a specific shape and is where the substrate binds to. The substrate is the reactants that the enzyme is interacting with.
Lock and Key Theory
The lock and key theory is a model developed by early scientists to explain how enzymes catalyse substrate reactions. The steps are explained below:
1. Enzyme has an active site which is exactly complementary to the substrate.
2. The substrate collides with the enzyme and fits into the active site. An enzyme-substrate complex is formed.
3. The enzyme catalyses the reaction forming an enzyme-product complex.
4. The products are released.

 Theory of induced fit
The theory of induced fit was developed by scientists and is now widely accepted as a better explanation of how enzymes work. This theory opposes the view that the active site and substrate fit together perfectly like a puzzle. The steps are explained below:
1. Enzyme has an active site which is not exactly complementary to the substrate.
2. When the substrate collides with the enzyme, the active site changes shape to fit the substrate more specifically. This forms an enzyme-product complex with a tighter fit- called the induced fit.
3. The enzyme catalyses the reaction forming an enzyme-product complex.
4. The products are released.

How is the activation energy decreased?
Enzymes work by binding one or more substrates which lower the activation energy. There are two ways enzymes do this depending on the type of reaction:
1) Bond breaking
o When the substrate fits into the enzyme’s active site, it puts stress on the bonds, so they are more easily broken.
2) Bond forming
o If two substates need to be joined, when the substances fit into the enzyme’s active site it holds them closer together.
o This reduces the repulsion between the two substrates so the molecules can bond more easily.