Carbohydrates - disaccharides Flashcards
what is a disaccharide
made when two monosaccharides are joined together. they are sweet and soluble like monosaccharides
what are the most common monosaccharides
maltose, sucrose and lactose
which disaccharides are reducing and which ones are non reducing
maltose and lactose are reducing sugars and sucrose is non reducing
how do two monosaccharides join together
they are joined together by a glycosidic bond during a condensation reaction
what is maltose (malt sugar) made up of
glucose + glucose
what is sucrose (table sugar) made up of
fructose + glucose
what is lactose (milk sugar) made up of
glucose + galactose
how do two glucose molecules form maltose
the two OH’s (one in carbon 1 and one in carbon 4) are so close together they react forming a covalent bond called a glycosidic bond between the two glucose molecules. the glycosidic bond is called an alpha 1-4 glycosidic bond
give two disaccharides that are formed from an alpha 1-4 glycosidic bond
alpha glucose + alpha glucose —-> maltose
alpha glucose + fructose —–> sucrose
give two disaccharides that are formed from a beta 1-4 glycosidic bond
beta galactose + alpha glucose —–> lactose
beta glucose + beta glucose ——> cellobiose
how do disaccharides form (detail)
when they join, a condensation reaction occurs to form a glycosidic bond. two hydroxyl groups line up next to each other from which a water molecule is removed. this leaves an oxygen atom acting as a link between the two monosaccharide units
how are disaccharides broken down
they are broken down into monosaccharides by a hydrolysis reaction which requires the addition of water. the water provides a hydroxyl group and a hydrogen which help the glycosidic bond to break
