BIO - enzymes

• enzymes are biological catalysts
• there are chemical reactions in our body constantly - they need to be carefully controlled to get the right amount of substances.
• a catalyst is a substance which increases the speed of a reaction, without being changed or used up in the reaction.
• enzymes are all large proteins and all proteins are made of chains of amino acids.
• every enzyme has an active site with a unique shape that fits onto the substrate involved in a reaction.
• enzymes usually only catalyse one specific reaction.
• the substrate fits onto the enzyme's active site - this is called the lock and key model
• if the substrate doesn't fit the enzyme's active site, then the reaction won't be catalysed
• the active site changes shape a little as the substrate binds to it to get a tighter fit - this is called the induced fit model of enzyme action
• changing the temperature changes the rate of enzyme activity
• at first, a higher temperature increases the rate, but if it gets too hot, some of the bonds holding the enzyme together break - this changes the shape of the enzyme's active site, so the substrate won't fit anymore. the enzyme is said to be denatured
• when the active site of the enzyme has changed, the enzyme is denatured
• all enzymes have an optimum temperature that they work best at
• the PH affects enzymes
• if the PH is too low or too high, the PH interferes with the bonds holding the enzymes together.
• all enzymes have an optimum PH that they work best at
• digestive enzymes break down big molecules
• starch, proteins and fats are big molecules --> they are too big to pass through the walls of the digestive system, so digestive enzymes break these big molecules down into smaller ones. these smaller molecules can pass easily through the walls of the digestive system, allowing them to be absorbed into the bloodstream.
• amylase converts carbohydrates into simple sugars, like glucose and maltose
• amylase breaks down starch into glucose
• amylase is produced in the salivary glands, pancreas and small intestine
• amylase functions in the mouth and small intestine
• amylase works best in a neutral PH e.g. PH 5/6/7
• protease breaks down proteins into amino acids
• protease is produced in the stomach, pancreas and small intestine
• protease functions in the stomach and small intestine
• protease works best at a low, acidic PH e.g. 1/2/3
• lipase breaks down lipids into fatty acids and glycerol
• lipase is produced in the pancreas and small intestine
• lipase functions in the small intestine
• lipase works best at a high, alkaline PH e.g. 7/8/9....
• bile neutralises the stomach acid and emulsifies fats
• bile is produced in the liver and its stored in the gall bladder before its released into the small intestine
• the hydrochloric acid in the stomach makes the PH too acidic for enzymes in the small intestine to work properly.
• bile is alkaline - it neutralises the acid and makes conditions alkaline --> the lipase enzymes work best in these alkaline conditions
• bile emulsifies fats - it breaks down the fat into tiny droplets, this gives a much bigger surface area for the lipase enzyme to work on, which makes digestion faster