Introduction to Enzymes in a Snap! Unlock the full A-level Biology course at http://bitly.com/2U3VNLF created by Adam Tildesley, Biology expert at SnapRevise and graduate of Cambridge University.

The key points covered of this video include:

1. Chemical reactions in organisms
2. Introducing enzymes
3. Activation Energy
4. Active sites

Chemical Reactions in Organisms

Organisms need to carry out metabolic reactions in order to survive. These reactions need to happen quickly so that organisms can respond to changes in their environment. Reactions can be sped up by increased temperatures. High temperatures can damage cells. Another way to speed up reactions is to use a catalyst. Biological catalysts for metabolic reactions are called enzymes. A catalyst is a chemical that speeds up the rate of reaction and remains unchanged and reusable at the end of the reaction.

Introducing enzymes

All living organisms need to carry out metabolic reactions as part of staying alive. To carry out metabolic reactions quickly, cells use proteins called enzymes. Any molecule that can have a reaction catalyzed by an enzyme is called a substrate. Any molecule that can have a reaction catalyzed by an enzyme is called a substrate. Substrates bind to the reactive part of an enzyme, called its active site. A substrate will only bind with an active site if it is the correct shape. Therefore every substrate will have a specific enzyme that it can bind with. Therefore every substrate will have a specific enzyme that it can bind with. The ability of an enzyme to function is affected by the 3D shape of its active site. The shape of its active site can be affected by factors like pH, temperature and the presence of inhibitors or cofactors.

Activation Energy

In a liquid, molecules are always moving and colliding with each other.
If the right molecules collide with sufficient energy then a chemical reaction will occur.
All reactions require an certain amount of kinetic energy to start- this is called the activation energy. If more molecules have enough kinetic energy to react then there will be more ‘successful’ collisions every second. Activation energy is the energy required to start a reaction. A reaction with lower activation energy will occur faster. This is because there will be more molecules with sufficient energy to react. The change in energy that occurs during a reaction can be shown using a graph. Enzymes catalyze reactions by lowering the activation energy required for a reaction to occur. This form of catalysis also allows reactions to occur at lower temperatures.

Active Sites

Enzymes can only catalyse a reaction if a substrate binds to its active site. Most metabolic reactions occur in a series of small steps. Active sites contain reactive molecules that can carry out these small steps in a controlled way with lower activation energy. When a substrate (or substrates) binds to the active site it is held in a specific orientation that facilitates its reaction. The active site can also apply physical pressure to a substrate, further lowering activation energy.

Summary

Enzymes are biological catalysts that speed up reactions without being depleted in the process
Enzymes are proteins with an active site that binds to a substrate
Enzymes catalyse reactions by reducing the activation energy required for the reaction to occur