Carbohydrates

A reduction is a reaction involving the gaining of electrons - all monosaccharides and some disaccharides are reducing sugars. This means they can donate electrons.

To test for a reducing sugar, a sample (in its liquid form) is placed in a boiling tube. An equal volume of Benedict's reagent is then added before the mixture is heated in a boiling water bath for 5 minutes.

Any reducing sugars will react with the copper ions in Benedict's reagent, resulting in the addition of electrons to the Cu2+ ions which reduces them to Cu+ ions. If reducing sugars are present, a brick-red precipitate will be formed. The more reducing sugars present, the more precipitate forms - making the solution appear more red.

1.A sample (in its liquid form) is place in a boiling tube

2. An equal volume of Benedict's reagent is added.

3. The mixture is heated gently in a boiling water bath for 5 minutes.

Non-reducing sugars don't react with Benedict's reagent so the solution will remain blue after heating - indicating a negative result. Sucrose is the most common reducing sugar.

A few drops of iodine is dissolved in a potassium iodide solution and then mixed with a sample. If the soultion's colour;

• changes from yellow/brown to purple/black, starch is present
• remains yellow/black, starch is not present

Beta glucose molecules are unable to join together in the same way that alpha glucose can. In order to join, alternative beta glucose molecules are turned upside down. When a polysaccharide is formed in this way it cannot form branches or coil. Instead a straight chain molecule called cellulose is formed.

Cellulose molecules make hydrogen bonds to form microfibrils. These join together to form macrofibrils which are strong and insoluble as well as used to form cell walls.

Many Alpha Glucose Molecules joined together by glycosidic bonds.

Starch is a cemical Energy Store for plants.

Amylose is formed when 1-4 glycosidic bonds join together. The angle of the bond means that the glucose chain twists to form a helix, further stabilised with hydrogen bonding.

It is a compact molecule and less soluble than the individual glucose molecules.

Amylopectin is formed with glycosidic bonds which were formed by condensation reaction between Carbon 1 and Carbon 6 on two molecules. Also made with 1-4 glycosidic bonds between alpha glucose molecules, similar to amylose.

It has a branched structure and is insoluble

Its a chemical energy store for animals and fungi with more branches than Amylopectin –  making it more compact.

The Coils and branches make them very compact – which is ideal for storage.

Branches mean that glucose molecules can be added or removed – speeds up process of storing or releasing molecules required by the cell. The molecuole is also insoluble

Requirerelease glucose for respiration, starch or glycogen undergo this.

Hydrolysis is the addition of water molecules – reverse of condensation - and is catalysed by enzymes.

Its when the two hydroxyl groups between two glucose molecules react. Two hydrogen atoms and an oxygen atom are removed from the glucose monomer -they join to form a water molecule.

A glycosidic bond forms between Carbon 1 and 4 on the glucose molecules.