1. Enzymes
Most of the food we eat is complex carbohydrates, proteins and lipids. These must be broken down to be absorbed into the body.
The chemical reactions required to break them down would be too slow without enzymes.
Enzymes are biological catalysts– they speed up chemical reactions.
Enzymes are required for most of the chemical reactions that occur in organisms. These reactions occur in the breakdown of chemical molecules, which we see in the digestive system.
Enzymes are also involved in the building up of chemical molecules elsewhere in the body.
Enzymes are proteins that have a complex 3D shape. Each enzyme has a region called an active site.
The substrate – the molecule or molecules taking part in the chemical reaction – fits into the active site. Once bound to the active site, the chemical reaction takes place .
Temperature
At low temperatures, the number of successful collisions between the enzyme and substrate is reduced because their molecular movement decreases. The reaction is slow.
The human body is maintained at 37°C as this is the temperature at which the enzymes in our body work best. This is not true of the enzymes in all organisms.
Higher temperatures disrupt the shape of the active site, which will reduce its activity, or prevent it from working. The enzyme will have been denatured.
Enzymes therefore work best at a particular temperature.
Enzyme action
Proteins are chains of amino acids joined end to end. This chain is not straight – it twists and folds as different amino acids in the chain are attracted to, or repel each other.
Each enzyme is made from proteins made of these twisting and folding amino acids, and therefore the enzyme has a unique shape. This structure is held together by weak forces between the amino acid molecules in the chain.
High temperatures will break these forces. The enzyme, including its active site, will change shape and the substrate will no longer fit. The rate of reaction will be affected, or the reaction will stop.

2. When the temperature is high:
Questions
Name 3 complex food molecules _______________________________________________________________________________________
Why must they be digested? __________________________________________________________________________________________
What are enzymes? What do they do? __________________________________________________________________________________
____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
4. What is the substrate? ________________________________________________________________________________________________
5. What temperature do enzymes work best at? ______________________________________________________________________________
6. What does the word optimum mean? ____________________________________________________________________________________
7. What does denatured mean? Explain in detail. _____________________________________________________________________________
__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
8. Draw a diagram of the enzyme and substrate, label the active site.
When the temperature is high:
The enzyme becomes ___________(destroyed).
This means that it has changed _________and is no longer complementary for the substrate. i.e. the _____ doesn’t fit the lock anymore.
This is irreversible, once the enzyme has been denatured it cannot regain it’s shape.
Remember! Enzymes are NOT cells or alive, therefore they cannot be killed!
When the temperature is low:
The molecules of enzyme and substrate do not have enough kinetic _________to collide. Because there are few collisions, the reaction is much ____________This is reversible. The reaction can be speeded up by increasing the temperature.