in this article we're going to talk about disaccharides disaccharides are carbohydrates that contain two sugar units the first one we're going to talk about is sucrose sucrose is composed of the monosaccharides glucose and fructose sucrose is basically table sugar you've seen it almost every day now let's draw the structure of sucrose so this is glucose I'm gonna draw this a little bit bigger so it's easier to see glucose is the structure on the left it forms a six membered ring fructose is the structure on a right it forms a five membered ring but both glucose and fructose contain six carbon atoms they have the same chemical form of c6h12o6 so that's the structure of sucrose now the bond that holds them together that connects glucose and fructose this is known as a glycosidic bond one thing I do want to mention is that these endpoints here are not carbon atoms it may look like a carbon atom but it's not so sometimes you could draw it this way if you want to avoid a confusion so now it doesn't look like a carbon atom so that's how you can draw the structure of sucrose to make sucrose we need to combine glucose and fructose they will have the same chemical formulas c6h12o6 the chemical formula for sucrose is c12 h22 o11 and the only thing that's missin to balance the equation is water so this is an example of a dehydration synthesis reaction it's dehydration because we're losing water but it's also a synthesis reaction because we'll take in two smaller components glucose and fructose and were synthesizing sucrose now let's say if we were to start with sucrose and we were to add water into it you may need to add an acid catalyst to speed up the process but sucrose plus water can go in reverse it can break down into glucose and fructose so in this direction the reaction is no longer a dehydration synthesis reaction but it's called a hydrolysis reaction hydro were using water lysis means to split apart so we're using water to split apart sucrose into its component forms glucose and fructose now there are some other disaccharides that you need to be familiar with and one of them is lactose lactose is basically milk sugar lactose is a disaccharide made up of glucose and it's c4 epimer galactose another disaccharide is a maltose maltose is composed of two units of glucose so those some disaccharides that you may need to be familiar with lactase whenever you hear the end in ace that is an enzyme lactase is the enzyme that breaks down lactose into glucose and galactose so notice the difference between lactose and lactase whenever you see the suffix os-- that tells you you're dealing with a carbohydrate think of glucose fructose galactose it's healthy if the sugar but if you hear the word ace or the suffix ace you're dealing with a protein based enzyme so that's it for this video so now you're familiar with the three most common disaccharides lactose maltose and sucrose