Enzyme Catalysis

Enzyme Catalysis

Function of Enzymes

• Enzymes are biological catalysts that speed up chemical reactions in cells.
• They work by lowering the activation energy required for a reaction, making it happen more quickly and efficiently.
• Each enzyme is designed to catalyse a specific reaction, and will only bind with the corresponding substrate – this is known as the lock and key model.

Enzyme Structure

• Enzymes are proteins made up of long chains of amino acids.
• Their structure determines the type of reaction they can catalyse, since the enzyme and substrate need to fit together perfectly.
• The specific place on the enzyme where the substrate binds is called the active site.

Enzyme-Substrate Complex

• The formation of the enzyme-substrate complex is the first step in enzyme catalysis.
• The substrate binds to the active site of the enzyme, forming a sort of ‘molecular handshake’.
• After the reaction, the enzyme releases the products and is free to catalyse another reaction.

Factors Affecting Enzyme Activity

• Several conditions can affect the rate at which enzymes work, including temperature, pH, and substrate concentration.
• Temperature: Each enzyme has an optimum temperature at which it works best. Too low, and the reaction rate will be slow; too high, and the enzyme could denature and lose its functional shape.
• pH: Similar to temperature, each enzyme also has an optimum pH. Deviations can lead to a loss in enzyme functionality.
• Substrate Concentration: The higher the substrate concentration, the faster the reaction - up to a point. After all the active sites are filled, further increases in substrate concentration have no effect.

Enzyme Inhibition

• Certain molecules can interfere with enzyme function, these are known as inhibitors.
• Competitive inhibitors bind to the active site of an enzyme, blocking the substrate from binding.
• Non-competitive inhibitors bind to a different part of the enzyme, changing its shape so the substrate can no longer bind.
• In some cases, inhibition can be reversed by increasing the substrate concentration. This is not possible with non-competitive inhibitors.

Regulation of Enzyme Activity

• Cells can control the amount and activity of enzymes to regulate metabolic pathways.
• This can involve genetic control of enzyme production, and post-translational modification such as adding a phosphate group.
• Feedback inhibition is a mechanism where the end product of a metabolic pathway inhibits the activity of an enzyme early in the pathway, preventing the overproduction of the end product.