The importance of enzymesSpec 1.12
In short
Enzymes are biological catalysts that speed up reactions in cells, which would otherwise be far too slow to keep us alive. They are needed to build and break down large molecules: carbohydrates are made from and broken into sugars, proteins into amino acids, and lipids into fatty acids and glycerol. Different enzymes catalyse each reaction, because enzymes are specific.
Chemical reactions in living things would be far too slow to keep us alive without enzymes. Enzymes are biological catalysts that speed up reactions in cells. They are needed both to build large molecules and to break them down.
| Large molecule | Made (synthesised) from | Broken down into |
|---|---|---|
| Carbohydrates | Sugars | Sugars |
| Proteins | Amino acids | Amino acids |
| Lipids | Fatty acids and glycerol | Fatty acids and glycerol |
Different enzymes catalyse each of these reactions, because enzymes are specific. Breaking down large molecules into small ones is a vital job, and so is building the carbohydrates, proteins and lipids the body needs.
If asked what a catalyst does, say it speeds up a reaction and is not used up.
Quick check
What are proteins broken down into?
Show answer
Amino acids.
What does a catalyst do?
Show answer
It speeds up a reaction and is not used up.
Which reagent turns purple when protein is present?
Show answer
Biuret reagent (Triple only).
How can the energy in food be measured?
Show answer
By burning it to heat water and using the temperature change (calorimetry) (Triple only).
Written and checked against the Edexcel GCSE Combined Science (1SC0) specification · Updated October 2026