Edexcel GCSE Biology: Enzymes and Metabolism

Edexcel GCSE Biology: Enzymes and Metabolism

What are Enzymes?

Enzymes are biological catalysts. This means they speed up chemical reactions in living organisms without being used up themselves. Enzymes are proteins, and their specific shape allows them to bind to specific molecules called substrates. This binding creates an enzyme-substrate complex, which allows the reaction to occur much faster than it would without the enzyme.

How do Enzymes Work?

Enzymes have an active site that is specifically shaped to fit the substrate. When the substrate binds to the active site, it forms an enzyme-substrate complex. This binding puts stress on the bonds within the substrate molecule, making it easier for the reaction to occur. Once the reaction is complete, the products are released, and the enzyme is free to bind to another substrate molecule.

Factors Affecting Enzyme Activity

Several factors can affect the rate of enzyme-catalyzed reactions:

• Temperature: Enzymes have an optimal temperature at which they work best. Increasing the temperature initially increases the rate of reaction, but if the temperature gets too high, the enzyme can become denatured (lose its shape) and stop working.

• pH: Enzymes also have an optimal pH. Changing the pH too much can denature the enzyme.

• Substrate Concentration: Increasing the substrate concentration initially increases the rate of reaction, but eventually, the enzyme becomes saturated with substrate, and the rate levels off.

• Enzyme Concentration: Increasing the enzyme concentration increases the rate of reaction, as there are more enzymes to bind to the substrate.

Metabolic Pathways

Metabolic pathways are a series of interconnected reactions that occur in living organisms. These pathways are controlled by enzymes, and they allow the organism to build up (anabolism) or break down (catabolism) complex molecules.

Examples of Metabolic Pathways:

• Photosynthesis: This anabolic pathway uses light energy to convert carbon dioxide and water into glucose and oxygen.
• Respiration: This catabolic pathway breaks down glucose to release energy in the form of ATP.

Key Concepts to Remember:

• Active Site: The specific region of an enzyme that binds to the substrate.
• Substrate: The molecule that an enzyme acts upon.
• Enzyme-Substrate Complex: The temporary combination of an enzyme and its substrate.
• Denaturation: The loss of an enzyme's shape and function due to changes in temperature or pH.
• Metabolic Pathway: A series of linked chemical reactions catalyzed by enzymes.

Revision Tips:

• Practice drawing and labeling diagrams of enzyme-substrate complexes.
• Understand the factors affecting enzyme activity and be able to explain their effects.
• Learn the key examples of metabolic pathways, including photosynthesis and respiration.
• Use past papers to practice answering exam questions.

This tutorial provides a solid foundation for understanding enzymes and metabolism. Remember to review the specific details and applications within your Edexcel GCSE Biology textbook and revision materials. Good luck with your studies!