[Music] hi and welcome back to three slice lessons Cote UK by the end of this video you should be able to describe the enzymes in the digestive system you should then be able to describe the role of bile in the last video we looked at the digestive system we saw that large food molecules are digested by enzymes into smaller molecules these products of digestion of an absorbed into the bloodstream so in this video we're looking at the enzymes involved in digestion here's the first key fact about enzymes enzymes catalyze chemical reactions in other words they speed them up now enzymes are large protein molecules they've got a groove on their surface called the active site the operative site is where the substrate attaches to and the substrate is the molecule that the enzyme breaks down so I'm showing you here an enzyme and you can see the active site on the surface here's the substrate molecule and you can see that it fits perfectly into the active site the enzyme now breaks down the substrate into the products this shows the same enzyme and a different substrate this substrate does not fit into the active site so the enzyme cannot break down this substrate so remember that enzymes are specific the substrate must fit perfectly into the active site scientists call this the lock and key theory okay so let's look at the specific enzymes in the digestive system proteins are broken down by enzymes called proteases and we find these in the stomach the pancreatic fluid on the small intestine now I'm showing you a drawing of the structure of proteins here proteins are long chains of chemicals called amino acids when we digest proteins the protease enzymes convert the protein back to the individual amino acids which are then absorbed into the bloodstream when the amino acids are then absorbed by the body cells that join together in a different order to make human proteins we're going to look now at the digestion of starch which is an example of a carbohydrate I'm showing you the structure of starch here as you can see starch consists of a chain of glucose molecules now carbohydrates like starch are broken down by enzymes called carbohydrates and in the case of starch the specific enzymes called amylase when carbohydrates like starter digested we produce simple sugars like this amylase is found in the saliva and it's found in the pancreatic fluid okay we're going to look now at the digestion of lipids and lipids have this structure a lipid molecule consists of a molecule of glycerol attached to three molecules of fatty acids and again you could be asked that in your exam lipid molecules are digested by the enzyme lipase and this produces glycerol and fatty acids like this we find lipase and the pancreatic fluid and also in a small intestine now the digestion of lipids also involves bile so we're going to finish by looking at that biles made in the liver and it's stored in the gallbladder now I'll help to speed up the digestion of lipids but bile is not an enzyme this shows a lipid droplet and lipase enzymes bile converts large lipid droplets into smaller droplets like this scientists say that bile emulsifies the lipid this massively increases the surface area of the lipid droplets under this increases the rate of lipid breakdown by lipase now biles also alkaline and this allows it to neutralize stomach acids creating alkaline conditions in the small intestine and again this increases the rate of lipid digestion by lipase remember that you'll find plenty of questions on enzymes in the digestive system in my vision workbook which you can get by clicking on the link above ok so hopefully now you should be able to describe the enzymes in the digestive system you should then be able to describe the role of bile [Music] you