BIOLOGICAL MOLECULES
Chemical Elements
• Most of the molecules in living organisms fall into three categories: YOUR NOTES
carbohydrates, proteins and lipids
• These all contain carbon and so are described as organic molecules
MOLECULE CHEMICAL ELEMENTS
CARBOHYDRATE CARBON, OXYGEN AND HYDROGEN
PROTEIN ALL CONTAIN CARBON, OXYGEN, HYDROGEN AND NITROGEN
AND SOME CONTAIN SMALL AMOUNTS OF OTHER ELEMENTS
SUCH AS SULPHUR
4.1LIPIDCARBOHYDRATES,
CARBON, OXYGEN AND HYDROGEN
FATS & PROTEINS
Carbohydrates
Carbohydrates are substances that include sugars, starch and
cellulose; they contain carbon, hydrogen and oxygen.
Sugars are carbohydrates that have relatively small molecules;
they are soluble in water and they taste sweet.
One type of sugar is glucose- C6H12O6. Glucose is the way that
carbohydrates are transported around the human body. Glucose
dissolves in blood plasma, which delivers it to every cell.
Glucose can link together in chains to form large molecules like
glycogen.
In plants, glucose molecules are linked together to make starch. It
is used in respiration to release energy.
Cellulose is also formed by carbohydrates. It is used in making
plant cell walls.
Fats
• Fats and oils also contain carbon, hydrogen and oxygen but each
molecule contains less oxygen than carbohydrates.
• Their basic unit is one glycerol and three fatty acids
• The fatty acids vary in size and structure
• Lipids are divided into fats (solids at room temperature) and oils
(liquids at room temperature)
BIOLOGICAL MOLECULES
Proteins
Long chains of amino acids
There are about 20 different amino acids YOUR NOTES
When amino acids are joined together a protein is formed
The amino acids can be arranged in any order, resulting in hundreds
of thousands of different proteins
Even a small difference in the order of the amino acids results in a
different protein being
MOLECULE formedELEMENTS
CHEMICAL
They contain four elements- carbon, hydrogen, oxygen and nitrogen
Some can also contain a small quantity of sulfur
All enzymes are proteins
Describing Food Tests
Test for glucose (a reducing sugar)
4.1 • Add Benedict’s solution
CARBOHYDRATES, FATSinto sample solution in test tube
& PROTEINS
• Heat at 60 – 70 °c in water bath for 5 minutes
• Take test tube out of water bath and observe the colour
• A positive test will show a colour change from blue to orange or brick
red
BIOLOGICAL MOLECULES
Test for protein
• Add drops of biuret solution to the food sample
• A positive test will show a colour change from blue to violet / purple YOUR NOTES
MOLECULE CHEMICAL ELEMENTS
4.1 CARBOHYDRATES, FATS & PROTEINS
Test for starch using iodine
We can use iodine to test for the presence or absence of starch in a food sample.
• Add drops of iodine solution
to the food sample
• A positive test will show a
colour change from orange–
brown to blue-black
BIOLOGICAL MOLECULES
Test for lipids
• Food sample is mixed with ethanol and shaken
• The ethanol is added to an equal volume of cold water YOUR NOTES
• A positive test will show a cloudy emulsion forming
MOLECULE CHEMICAL ELEMENTS
4.1 CARBOHYDRATES, FATS & PROTEINS
Test for vitamin C
• Add DCPIP solution to a test tube
• Add a small amount of food sample (as a solution)
• A positive test will show the blue colour of the dye
disappearing
BIOLOGICAL MOLECULES
Describing DNA Structure
• DNA, or deoxyribonucleic acid, is the molecule that contains the
YOUR NOTES
instructions for growth and development of all organisms
• It consists of two strands of DNA wound around each other in what is
called a double helix
MOLECULE CHEMICAL ELEMENTS
4.1 CARBOHYDRATES, FATS & PROTEINS
• The individual units of DNA are called nucleotides
• There are four different bases, Adenine (A), Cytosine (C), Thymine (T)
and Guanine (G)
• The bases on each strand pair up with each other, holding the two
strands of DNA in the double helix
• The bases always pair up in the same way:
• Adenine always pairs with Thymine (A-T)
• Cytosine always pairs with Guanine (C-G)
