L3 - Enzyme Activity

objectives

• Define enzymes as proteins that act to increase the rate of chemical reactions (digestion) in the body

Living Reactions

Reactions that happen inside an organism are part of processes called metabolism. For example:

• Respiration
• Digestion
• Growth
• Germination
• Photosynthesis

How Enzymes work

Enzymes speed up a reaction but are unchanged at the end of it. Chemicals that do this are called catalysts.

They can be used over and over again but are not used up in the reaction.

Enzymes are very large biological molecules called proteins that are used by the body to break down large molecules into small molecules.

They are specific which means there is an enzyme for every different type of molecule the human body can digest.

The large molecule the enzyme breaks down is called the substrate.

These fit in the active site which is a specific area of enzyme that is shaped to allow other molecules to fit into it to undergo reaction. The active site is the most vital part of enzyme function.

In the active site the substrate is broken down into the products.

Describing Enzyme Reactions

In a normal chemical reaction - the reactants go on the left hand side of the arrow and the products go on the right hand side. Anything that is involved in the reaction but not changed can be placed over the central arrow in Biology.

This means that enzymes - as catalysts - are placed over the arrow.

The molecule the Enzyme breaks down is a reactant and so on the left

The molecules that the made in the reaction are Products.

Enzymes as Catalysts

Enzymes are biological catalysts.

They are biological since they are produced by living cells.

They are catalysts since they increase the rate of a reaction without undergoing permanent change. This means enzymes can be reused repeatedly and are therefore effective in small amounts.

Lock & Key Model

•Enzymes have a specific 3D structure

•They exactly match the shape of a molecule of substrate

The shape of the substrate (key) exactly fits the active site of the enzyme (lock). They have shapes that are complementary to each other.

Steps of the Lock and Key Model

1. Substrate fits into active site of enzyme - this is called binding

2. This forms the Enzyme/Substrate Complex

3. A reaction takes place - making the Enzyme/Product Complex

4. The Products are released

Lock & Key Model - Maltose and Maltase Example

An important note is that Maltase will not break down any other molecule - it is specific to maltase.

Video on Enzymes