1 - STRUCTURES AND FUNCTIONS IN LIVING ORGANISMS 

Enzymes 

• Catalysts produced by living things - biological catalysts
• Catalyst - a substance which increases the speed of a reaction without being changed or used up in the process 
• Allows individual reactions to be sped up (without raising temperature and speeding up unwanted reactions too/damaging cells) - reduce the need for high body temperatures
• Only have enzymes to speed up useful chemical reactions (metabolic reactions) 
• All proteins (chains of amino acids) 

Specificity -

• Substrate - molecule changed in a reaction 
• An enzyme molecule has an active site (where a substrate then joins on) 
• Suited to one particular reaction - needs correct substrate to fit into active site 
• Lock and key model: 

Temperature - 

• Changing temperature changes rate of an enzyme-catalysed reaction 
• Higher temperature increases reaction rate at first (more heat - particles have more energy, higher collision rate) 
• Lower temperatures slow reaction down - lower collision rate 
• Denaturing - If the enzyme gets too hot, some of the bonds break and the shape of the active site changes (substrate doesn't fit anymore). Reaction eventually stops once all enzymes are denatured. It's irreversible. 
• Optimum temperature - reaction is at its fastest just before it gets too hot and denatured. (eg: most important enzymes in humans have an optimum temperature of 37 degrees) 

Effect of temperature on enzyme activity - 

How fast a product appears: 
-Catalase catalyses the breakdown of hydrogen peroxide into water and oxygen 

• Collect oxygen given off - how much in a set time? 
• Use a water bath - how does temperature affect amount of product produced/activity level of catalase? 
• Control any variables (eg: enzyme concentration, pH, volume of solution etc.) 

How fast a substrate disappears: 
-Amylase catalyses breakdown of starch to maltose 

• Use iodine to test for starch (iodine solution turns from brown/orange to blue/black) 
• Time how long it takes for starch to disappear (sample starch solution regularly) - compare 
• Use water bath - how does temperature affect activity of amylase? 
• Control all variables

pH - 

• Affects enzymes 
• Too high/low - interferes with bonds in enzyme, can cause it to become denatured 
• Optimum pH - (generally pH7), pH at which the rate of reaction is the fastest 
• eg: pepsin (breaks down proteins in stomach), optimum pH = pH 2