Explain the role of enzymes in digestion with reference to amylase, protease and lipase.

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IGCSE Biology - 7.2 Human Nutrition - Enzymes in Digestion

IGCSE Biology 0610

Topic: 7.2 Human nutrition – alimentary canal

Objective: Explain the role of enzymes in digestion with reference to amylase, protease and lipase.

Enzymes are biological catalysts. They speed up chemical reactions in the body without being used up themselves. In the digestive system, enzymes play a crucial role in breaking down large, complex food molecules into smaller, simpler molecules that can be absorbed into the bloodstream.

Enzymes and their Action

Different enzymes are responsible for digesting different types of food molecules. The main digestive enzymes are amylase, protease, and lipase.

Amylase

Role: Amylase digests starch into maltose.

Source: Salivary glands in the mouth and the pancreas.

Conditions for optimal activity: Optimal pH is around 6-7 (slightly acidic). Optimal temperature is around 37°C (body temperature).

Diagram:

Suggested diagram: A diagram showing starch molecules being broken down into maltose molecules with amylase enzyme.

Protease

Role: Protease digests protein into smaller peptides and amino acids.

Source:

  • Salivary glands (lingual glands) - Ptyalin
  • Pancreas - Pepsinogen (converted to pepsin in the stomach)

Conditions for optimal activity: Optimal pH is around 2-3 (very acidic) for pepsin in the stomach, and around 7 (slightly acidic) for pancreatic protease.

Diagram:

Suggested diagram: A diagram showing protein molecules being broken down into peptides and amino acids with protease enzyme.

Lipase

Role: Lipase digests fats (lipids) into fatty acids and glycerol.

Source: Pancreas.

Conditions for optimal activity: Optimal pH is around 7 (slightly acidic).

Diagram:

Suggested diagram: A diagram showing fat molecules being broken down into fatty acids and glycerol with lipase enzyme.

Enzyme Action Table

Enzyme Substrate Product Optimal pH Optimal Temperature
Amylase Starch Maltose 6-7 37°C
Protease Protein Peptides & Amino Acids 2-3 (Pepsin), 7 (Pancreatic Protease) 37°C
Lipase Fats (Lipids) Fatty Acids & Glycerol 7 37°C

Enzyme Efficiency: Enzymes are effective because they lower the activation energy of the reaction. This means that less energy is required for the reaction to occur, and the reaction proceeds much faster. Enzymes are specific – each enzyme typically only works on one particular substrate.

Factors Affecting Enzyme Activity:

  • Temperature: Enzymes have an optimal temperature. Too low, and the reaction is slow. Too high, and the enzyme denatures (loses its shape and function).
  • pH: Enzymes have an optimal pH. Deviations from this pH can also cause denaturation.
  • Substrate Concentration: As substrate concentration increases, the rate of reaction increases until all enzyme active sites are occupied. Beyond that point, the rate plateaus.