AQA GCSE FOUNDATION Biology: Enzymes and Digestion

Enzymes and Digestion

What are Enzymes?

Enzymes are biological catalysts. This means they speed up chemical reactions in living organisms without being used up in the process. Enzymes are proteins with a specific 3D shape, which allows them to bind to specific molecules called substrates.

How do Enzymes Work?

• Lock and Key Model: Imagine an enzyme as a lock and the substrate as a key. The enzyme has a specific active site, like a keyhole, where the substrate fits perfectly. This precise fit ensures that only the correct substrate can bind to the enzyme.
• Induced Fit Model: This is a more modern model. It suggests that the active site changes shape slightly as the substrate binds, creating a tighter fit. This ensures that the enzyme can work effectively.

Enzymes in Digestion

Digestion is the process of breaking down large food molecules into smaller ones that can be absorbed by the body. This process relies heavily on enzymes.

Here are some key enzymes involved in digestion:

• Amylase: Breaks down starch (a complex carbohydrate) into simpler sugars like maltose.
  • Found in saliva and pancreatic juice.
• Protease: Breaks down proteins into amino acids.
  • Examples include pepsin (found in the stomach) and trypsin (found in the small intestine).
• Lipase: Breaks down fats (lipids) into fatty acids and glycerol.
  • Found in pancreatic juice.

How Enzymes Aid in Breaking Down Nutrients

• Speeding Up Reactions: Enzymes dramatically increase the rate at which food molecules are broken down. Without enzymes, digestion would take far too long.
• Specific Breakdown: Each enzyme has a specific role, ensuring that only certain types of molecules are broken down. This allows for efficient and controlled digestion.
• Optimum Conditions: Enzymes work best under specific conditions, such as temperature and pH. For example, pepsin in the stomach works best in acidic conditions, while trypsin in the small intestine works best in alkaline conditions.

Summary

Enzymes are essential for digestion. They act as biological catalysts, speeding up the breakdown of large food molecules into smaller, absorbable units. Each enzyme has a specific role, working under optimal conditions to ensure efficient and controlled digestion.