2.4.1 The Role Of Enzymes

Question 1

Enzymes as Catalysts

Answer 1

Enzymes are biological catalysts
- ‘biological’ because they function in living systems
- ‘catalyst’ because they speed up the rate of chemical reactions without being used up or undergoing permanent change
Enzymes are globular proteins with complex tertiary structures
- some are formed from a single polypeptide, whilst others are made up of two or more polypeptides and therefore have a quaternary structure
Metabolic pathways are controlled by enzymes in a biochemical cascade of reactions
- virtually every metabolic reaction within living organisms is catalysed by an enzyme
- enzymes are therefore essential for life to exist

Question 2

Site of Action of Enzymes

Answer 2

All enzymes are proteins that are produced via the process of protein synthesis inside cells
Some enzymes remain inside cells, whilst others are secreted to work outside of cells
Enzymes can therefore be intracellular or extracellular, referring to whether they are active inside or outside the cell respectively
- intracellular enzymes are produced and function inside the cell
- extracellular enzymes are secreted by cells and catalyse reactions outside cells (e.g. digestive enzymes in the gut)

Question 3

Intracellular Enzymes Example

Answer 3

Catalase

Hydrogen peroxide is produced as a by-product of many metabolic reactions
It is harmful to cells
Catalase converts hydrogen peroxide into water and oxygen, preventing any damage to cells or tissues

Question 4

Extracellular Enzyme Examples

Answer 4

Amylase

Digestion is usually carried out by extracellular enzymes
This is because the macromolecules being digested are too large to enter the cell
Amylase is involved in carbohydrate digestion
- it hydrolyses starch into simple sugars
It is secreted by the salivary glands and the pancreas, for digestion of starch in the mouth and small intestine respectively

Trypsin

Trypsin is another extracellular digestive enzyme that is secreted by the pancreas enzymes and enters the small intestine
- it breaks proteins down into peptides and amino acids

Question 5

Extracellular Digestion Outside of the Body

Answer 5

In fact, some organisms can only feed using a from of extracellular digestion in which the digestive enzymes are actually secreted outside of their bodies
For example, the hyphae of fungi secrete the necessary enzyme directly onto the foods they are consuming (e.g. wood) so that the food is digested into smaller, simple molecules that the fungi can then absorb through the walls of the hyphae