Disaccharide is a type of carbohydrate therefore the elemental composition of disaccharide is C, H, O.
They are generally sweet, crystalline, and water soluble.
disaccharides are formed with the bonding of two monosaccharides (simple sugars) and a release of water molecule. The bond is called the glycosidic bond and it's a covalent bond formed by dehydration (release of H2O) as stated previously. Not all monosaccharides contribute to the formation of a disaccharide only hexoses (6C) do.
Shown below is how the molecular formula of disaccharide is obtained
C6H12O6 + C6H12O6 – H20 = C12H22O11
( I put it up like this w the (–) and = for explanation purpose)
Disaccharides are divided into three as Maltose, Sucrose and Lactose
1. Maltose ( aka malt sugar )
Two Glucose molecules bonds up with 1-4 glycosidic bond producing Maltose also releasing a H2O molecule.
Maltose is a reducing sugar.
+ note : In germinating seeds hydrolysis of starch gives maltose therefore the seeds are used in producing malt foods. Maltose is also used in brewing beer.
2. Sucrose
This most abundant disaccharide is produced with Glucose and fructose binding up with 1-2 glycosidic bond and releasing a H2O molecule This reaction is catalyzed by sucrase enzyme.
Sucrose is a non-reducing sugar.
+ note : Sucrose is stored in some plants such as Beta vulgaris (beetroot) and saccharum (sugarcane)
In many plants they store starch but they transport sucrose in phloem Main two reasons for this is high water solubility of sucrose and sucrose is less metabolically reactive so sucrose isn't utilized by cells of phloem while being transported.
3. Lactose
Glucose and Galactose molecules bonds up with 1-4 glycosidic bond producing lactose also releasing a H2O molecule.
lactose is a reducing sugar.
+ note : lactose is commonly found in animal milk and very rarely found in some bacteria and plants.
In case you don't know what reducing, non-reducing sugars and what the numbers written in front of glycosidic bond mean,
Reducing sugars are sugars where the anomeric carbon has an OH group attached that can reduce other compounds. Non-reducing sugars do not have an OH group attached to the anomeric carbon so they cannot reduce other compounds.
simply reducing sugars are capable of acting as a reducing agent and non-reducing sugars don't.
In 1-4, 1-2 glycosidic bonds the numbers represent how the two simple sugars are bonded for example 1-4 glycosidic bond states that the glycosidic bond is formed between the first carbon of one sugar and the 4th carbon of the other.
in short this is how I remember it :)
M S L
R N R
1-4 1-2 1-4