Monosaccharides
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(CH2O)n
If n=3, triose (glyceraldehyde)
If n=5, pentose (ribose)
If n=6, hexose (glucose, galactose)
Monosaccharides are used for
– Energy
– Building blocks
Can you…
Draw on the diagram where a glycosidic bond will form
and complete the diagram to show the disaccharide that
will be produced.
Can you…
Draw on the diagram where a glycosidic bond will form
and complete the diagram to show the disaccharide that
will be produced.
Examples of Disaccharides
Maltose
Formed from 2 glucose molecules, formed in germinating
seeds from the breakdown of starch, providing energy
Sucrose
Formed from 1 glucose and 1 fructose molecule
and is the form in which carbohydrates are
transported in the phloem in plants
Lactose
Formed from 1 glucose and 1 galactose
molecule, it is an energy source found in the
milk of nearly all mammals
Polysaccharides
Carbohydrates which are made from many linked monosaccharide
monomers form long chain-like molecules
called polymers.
glycogen
starch
polysaccharides
- made from glucose
monomers
cellulose
Starch
Made of α glucose molecules linked by glycosidic bonds.
Used as an energy store in plants.
Not soluble.
Forms solid grains inside plant cells (often inside chloroplasts).
The chains coil up into a basic spiral shape making the molecules
compact.
Hydrogen bonds hold the polysaccharide chain in the compact spiral
shape.
Glycogen
This is the storage polysaccharide in animals
(equivalent to starch in plants).
Found in liver and muscle cells where a store of energy is needed.
Many fungi also store glycogen.
Similar in structure to starch - but more branched.
Forms tiny granules inside cells which are usually associated with
smooth endoplasmic reticulum.
Each glycogen molecule contains a few 1000 glucose units.
Cellulose
Most abundant organic molecule.
It is very slow to decompose.
20-40% of the plant cell wall.
Made of β glucose units.
Every other β glucose is rotated through 180° - this makes the chains
straight, not coiled.
Hydrogen bonding between monosaccharide molecules in the chain
gives strength.
Hydrogen bonding between cellulose molecules cause bundles called
microfibrils to develop. These are held together in fibres.
A cell wall will have several layers of fibres running in different
directions - gives great strength almost equal to steel.
Provides support in plants and stops plant cells bursting.
Freely permeable to water and solutes.
Can you…
Draw on the diagram where a glycosidic bond will form
and complete the diagram to show the disaccharide that
will be produced.
Hydrolysis