- They have a general formula: Cx(H2O)n
- Saccharides are made from sugar molecules that are made from combinations of the elements carbon, hydrogen, and oxygen only.
- They are used for:
- Fuels for respiration (glucose).
- Energy storage molecules (starch and glycogen).
- Structural molecules (cellulose).
|– Single sugar units||– glucose|
NB: there are 2 types of glucose: alpha and beta
|– Used in respiration|
|– Fructose||– Found in fruit & honey|
|– Galactose||– Found in lactose|
|(All the above are hexose sugars: C6H12O6)|
|Disaccharides||– 2 single sugar units joined by a glycosidic bond.||– Maltose|
(2 glucose molecules)
|– Found in germinating seeds e.g. barley|
(Glucose and fructose)
|– Crystals used in cooking|
(Glucose and galactose)
|– Sugar found in milk|
|Oligosaccharides||– 3-10 sugar units.||Found in vegetables e.g. leeks, lentils, beans|
Polysaccharides (polymers) are long chains of glucose molecules.
- Found in muscle and liver cells for energy storage.
- Made of poly alpha glucose linked together.
- Insoluble because it has 1,4 and some 1,6 links, which form branches in the chain.
- Very compacted, thus good for storage.
- Found in amyloplasts (starch grains) inside plant cells for energy storage.
- Made of 2 types of molecules: amylose and amylopectin.
- Amylose molecule is a very long chain of glucose molecules with 1,4 links.
- Amylopectin is similar to glycogen.
- Insoluble and very compact.
- Made from poly beta glucose
- Main component of cell walls as it is a very strong structural molecule.
- Cellulose has no branches, so adjacent cellulose chains line up close.
- Hydrogen bonds between adjacent chains, creating very strong cellulose fibrils.
- Saccharides link together by condensation reactions, producing water. A glycosidic bond forms between the saccharide molecules.
- The opposite of a condensation reaction is hydrolysis. It requires water.
- Tests for saccharides:
- Iodine solution turns brown to blue/black in the presence of starch.
- Benedict’s solution turns blue to brick red in the presence of a reducing sugar.
- Non-reducing sugars (disaccharides and polysaccharides) will give a positive result to Benedict’s if heated in acid first.