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Summary IGCSE-biology-enzymes
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IGCSE-Biology-Enzymes. Summary of Enzymes (Triple award inculded)
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Enzymes:Chemical reactions that take place in a cell are called metabolic reactions. The sum of these is known as
the metabolism of the cell. These are catalysed by enzymes. Enzymes are biological catalysts. A catalyst
is a chemical which speeds up the rate of a reaction, without being used up itself. Enzymes are proteins,
and there are many different enzymes. Enzymes are needed because at normal body temperature
(37oC), chemical reactions needed to live would occur too slowly. For a chemical reaction to occur,
particles need to collide with sufficient energy. At low temperatures, particles have little kinetic energy,
so do not collide frequently enough.
The molecule an enzyme acts on is called the substrate.On the surface of an enzyme, there
is an area called the active site. Each different enzyme has a different shaped active site,
specific to a particular substrate.This is called the lock and key model.
The substrate enters the enzymes active site, which lowers the energy required for the
reaction to take place. The reaction then takes place, and products are formed.
There are many enzymes involved in digestion. These are considered extracellular enzymes, as they work
outside of cells. Digestive enzymes can be sorted into 3 classes:
- Carbohydrase: break down starch into sugars
- Protease: break down proteins into amino acids
- Lipase: break down lipids into fatty acids and glycerol
Class Enzyme Substrate Product Produced in Works in
Carbohydrase Amylase Starch Maltose Salivary glands, pancreas Mouth, small
intestine
Maltale Maltose Glucose Wall of small intestine Small intestine
Protease Pepsin Proteins Peptides Stomach wall Stomach
Trypsin Proteins Peptides Pancreas Small intestine
Peptides Peptides Amino Acids Wall of small intestine Small intestine
Lipase Lipase Lipids Glycerol & fatty PAncreas Small intestine
acids
There are optimum conditions for enzyme activity. These depend on the organism and the enzyme. In
humans, the optimum temperature is 37oC (body temperature). The optimum pH for most enzymes in
humans is pH 7, as the pH inside cells is neutral.
Hydrogen peroxide is a product of metabolism, that is toxic. It can’t be allowed to build up in cells.
Catalase breaks down hydrogen peroxide into water and oxygen.
2H2O2 → 2H2O + O2
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