Disaccharides

• When 2 monosaccharides have a condensation reaction, it forms a disaccharide and a water molecule; the bond between the reacting monosaccharides is a glycosidic bond
• Two α-glucose molecules join to form a maltose molecule (between carbons 1+4, called an α 1-4 glycosidic bond), disaccharide’s general formula: 2(CH_2O)n - H_2O
• Can be hydrolysed into its monosaccharide monomers by adding water, hydrolysis and condensation reactions are catalysed by a specific enzyme
• Maltose; Glucose + Glucose; Source of glucose(energy) in germinating seeds (formed in the breakdown of starch in the seed food store)
• Sucrose; Glucose + Fructose; The form that sugars are transported in green plants (in the phloem)
• Lactose; Glucose + Galactose; Milk Sugar, the energy source for young mammals
• Maltose and lactose are both reducing sugars but Sucrose is not (reactive carbonyl groups lost during the formation of the glycosidic bond) so gives a negative reaction (remains blue) when heated with Benedict's reagent
• Sucrose is a non-reducing sugar - this is because the reactive carbonyl groups in sucrose have been lost during the formation of the glycosidic bond; sucrose gives a negative reaction (remains blue) when heated with Benedict's reagent
• Test for non-reducing sugars; boil them with dilute hydrochloric acid to hydrolyse sugar to its constituent monosaccharides, neutralise by mixing with sodium hydroxide then retest with Benedict's reagent; should be positive