Catalyst:
- A catalyst is a substance that increases the rate of a chemical reaction and is not changed by the reaction.
- In other words, a catalyst speeds up a reaction without being used up.

Enzymes:
- Enzymes are proteins that speed up reactions without being used up.
- Hence enzymes function as biological catalysts.
- As the enzymes are not used up, they can be reused.

Importance of enzymes:
- Our body contains many different types of enzymes to carry out different functions.
- Some examples of enzymes are amylase, protease, and lipase.
  - Human saliva contains amylase, an enzyme that breaks down starch to maltose.
  - Protease is an enzyme that breaks down proteins to amino acids.
  - Lipase is an enzyme that breaks down lipids like the fats to fatty acids and glycerol.
- Without enzymes, our digestive system simply cannot function and will not be able to break down nutrients.
- Most reactions in our body require enzymes, such as DNA replication in cells, detoxification in liver, respiration and metabolism.
- Enzymes are important in all living organisms to sustain life as they speed up the reactions in our body.
- Enzymes such as lipase and protease are also present in biological washing powders. Such enzymes help to break down the fat and protein molecules in cloth stains, removing stains effectively.

Enzyme action:
- An enzyme works on a molecule known as a substrate.
- Enzymes contain an active site in which the substrate can fit in and bind.
- When the substrate binds with an enzyme, an enzyme-substrate complex is formed.
- It is within this complex that the reaction takes place and the product is released.
- The molecules formed at the end of the reaction are known as products.
- After the reaction is complete, the enzyme is free to work on another substrate again.

Complementary shape of an enzyme and its substrate:
- Enzyme’s active site and its substrate are complementary in shape.
- Every enzyme has a different active site, and only specific substrates, whose shape matches the enzyme’s active site, will be able to fit into the active site.
- Therefore a specific type of enzyme can only work on a particular substrate.
- For example, amylase works only on starch, protease works only on proteins and lipase works only on lipids like fat and oils.

Lock and key model:
- Enzymes are substrate specific.
- The enzymatic reaction resembles the lock and key model, where the enzyme is the lock whereas the substrate is the key.
- When the key fits the lock, the reaction will take place.
- However when the key and the lock do not fit, reaction will not take place.

5.01 - Enzymes (I)

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