14/8/2011
Biology Revision
Topic:Biological Molecules

4 Components of biological molecules

• Water
• Carbohydrates
• Proteins
• Fats

Water
It is made up of the elements Hydrogen and Oxygen
Functions:

• For digestion
• A major component of cells(cytoplasm,vacuole)
• A major component of blood
• As a solvent
• For transport
• As waste product
• To prevent dehydration

Carbohydrates
It is made up of the elements Carbon,Hydrogen,Oxygen

Glycogen-Referred to as "animal starch"

• Storage form of carbohydrates in animals and in fungi
• Made from glucose
• Excess glucose is joined together in a very long chain to form glycogen
• In mammals,stored mainly in liver and muscles
• Glycogen is broken down to glucose when energy is needed

Proteins
It is made up of the elements Carbon,Hydrogen,Oxygen,Nitrogen

• Sulfur and phosphorus are also present
• Built up from simpler compounds known as amino acids
• 22 naturally occuring amino acids in plant and animal proteins
• Amino acids link up with one another to form long chains

Fats
It is made up of the elements carbon,hydrogen and oxygen

• No generalised formula
• Energy-providing food
• Large molecules made up of fatty acids and glycerol

Testing For Biological Molecules

Testing for starch
Iodine Test

1. Place the food on a white tile
2. Place 2-3 drops of iodine onto the food
3. The food containing starch will turn blue-black where the iodine touches them

Testing for reducing sugars(glucose)
Benedict's Test

1. Add equal amount of Benedict's solution to some gluocose solution in a test tube
2. Shake the test tube and heat it in a beaker of boiling water for 3-5 minutes.
3. A red precipitate will form

Testing for proteins
Biuret's Test

1. Add equal amount of sodium hydroxide solution to some egg white solution in a test tube
2. Shake the mixture
3. Add 1% copper sulphate solution,drop by drop.Shake the test tube after every drop
4. A purple colour will form

Testing for fats
Ethanol Emulsion Test

1. Add some alcohol to a small drop of oil in a test tube.Shake the mixture
2. Add the same amount of water to the mixture
3. A white,cloudy emulsion will form