1. Enzymes
Learning Objectives

2. Learning Outcomes

3. What are enzymes?
Enzymes are biological catalysts – they speed up the chemical reactions that take place inside all cells, but without being used up in the process.
Enzymes are specific for a particular chemicall reaction.

4. What are enzymes made of?
Enzymes are protein molecules, and so are made up of amino acids.
These amino acids are joined together in a long chain, which is folded to produce a unique 3D structure.

5. Why are enzymes so specific?
Enzymes are very specific about which reactions they catalyze. Only molecules with exactly the right shape will bind to the enzyme and react. These are called the substrates.
Photo credit: JC Revy / Science Photo Library
The image shows a molecular computer graphics image of ribonuclease A, an enzyme involved in the destruction of messenger RNA (mRNA) in the cytoplasm of bacteria. At left is its substrate, shifted away from the active site. Enzymes are biological catalysts, proteins that speed up the rates of reactions within cells. Each enzyme is specific for a particular reaction; interaction occurs (typically as a weak bond) between an active site on the enzyme & a reactant (or substrate) due to the arrangement of mutually attractive groups of atoms. This image displays the molecular surface (blue) & polypeptide chain: colours are used to represent the polarity of constituent amino acids.
The part of the enzyme to which the reactant binds is called the active site.

6. Enzymes: true or false? Teacher notes
This true-or-false activity could be used as a plenary or revision exercise on enzymes, or at the start of the lesson to gauge students’ existing knowledge of the subject matter. Coloured traffic light cards (red = false, yellow = don’t know, green = true) could be used to make this a whole-class exercise.

7. What happens at the active site?
In the same way that a key fits into a lock, so a substrate is thought to fit into an enzyme’s active site. The enzyme is the lock, and the reactant is the key. + + ↔ ↔
enzyme
reactant +
enzyme-reactant complex ↔
products

8. The lock and key model Teacher notes
This four-stage animation demonstrates the principles of the ‘lock and key’ model. While showing the animation, the specific shape of the active site could be highlighted.
Suitable prompts could include:
What is special about the shape of the active site?
Is the enzyme the ‘lock’ or the ‘key’?

9. Factors affecting enzymes
Factors that affect the rate of a reaction include:
temperature
substrate concentration pH
surface area
enzyme concentration
pressure.
All enzymes work best at only one particular temperature and pH: this is called the optimum.
Different enzymes have different optimum temperatures and pH values.

10. Name the structure Teacher notes
This activity could be used to check students’ understanding of the lock and key model.