4. ENZYMES

4.1 Enzyme action

• Chemical reactions for growth are anabolic (building up) reactions and are catalysed by enzymes.
• Energy is released from large molecules in metabolic pathways with catabolic (breaking down) reactions which are catalysed by enzymes.
• Energy needs to be supplied for reactions to start - activation energy.
• Intracellular enzymes act within cells. E.g. Hydrogen peroxide is catalysed by the enzyme catalase to make sure its broken down into oxygen and water quickly as it is toxic. In both plant and animal tissue.
• Extracellular enzymes are released from cells to break down large nutrient molecules (digestion) into substrates for reactions within cells.
• Digestion of starch - mouth to small intestine. Starch polymers broken down to maltose wity amylase from salivary glands and pancreas. Maltose is then broken into glucose with maltase in small intestine so glucose is small enough to be absorbed into stomach lining and bloodstream.
• The lock and key hypothesis
• substrate molecule is drawn into enzyme active site
• Enzyme-substrate complex is formed
• Enzyme reaction forms enzyme-product complex
• Products are released from enzyme
• Induced fit hypothesis
• substrate molecule is drawn into enzyme active site
• enzyme changes shape as substrate binds, forming enzyme-substrate complex
• ES interactions forms enzyme-product complex. Substrate is bound to enzyme by weak chemical bonds
• End product is released and enzyme returns to previous shape

4.2 Factors affecting enzyme activity

• Temperate
• Denature - at high temperatures the active site changes shape
• Optimum temperature - 40 in human body, 70 in thermophillic, 5 in cold places
• pH
• Structure of enzyme alters irreversibly
• Substrate / enzyme concentration
• increase number of collisions

4.3 Enzyme inhibitors

• Competitive
• similar shape to active site so bind and inhibit binding of other enzynes and thereforeprevent it carring out the functions