4.
Biological molecules
NUTRIENT
• A nutrient is a substance which is needed for growth, repair and metabolism.
• These all contain carbon and so are described as organic molecules.
• The three main nutrients are:
1. Carbohydrates
2. Proteins
3. Lipids (fats and oils)
1. Carbohydrates
• Carbohydrates include starch and sugars, and their job is to
supply us with energy.
• May be simple- soluble molecules (glucose, fructose etc) or
complex- insoluble molecules (starch ,glycogen and cellulose).
• All contains C,H,O only
• Glucose – C6H12O6
• Source – bread, rice, cereals, potatoes, pasta, etc.
• Enzyme that breaks down carbohydrate –
Amylase/Carbohydrase
3 Types of Carbohydrates
1. Monosaccharides or Simple sugars: (readily soluble in water)
sugars with a single
Glucose Fructose Galactose
carbon ring
Found in Plants and Animals Plants Milk
2. Disaccharides (readily soluble in water)
sugars with a two
Sucrose Lactose Maltose
carbon rings
Glucose and Glucose and Glucose and
Constituents
Fructose Galactose Glucose
3. Polysaccharides or Complex sugars: : (not readily soluble in water)
many glucose
molecules joined Starch Glycogen Cellulose
together
Found in Plants Animals Plants
2. Proteins
• Long chains of amino acids.
• There are about 20 different amino acids.
• They all contain the same basic structure but
the ‘R’ group is different for each one.
• When amino acids are joined together a protein is
formed. General structure of amino acids
• 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 formed.
• Enzymes, Hormones and antibodies are also
made of proteins.
• Enzyme that breakdown protein is protease.
3. Fats
• Most fats (lipids) in the body are made up of triglycerides.
• 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).
• Butter, margarine, cooking oil, cheese and red meat are rich in fats.
• Fats are a more concentrated form of energy than carbohydrates, and a
gram of fat contains more than twice as much energy as a gram of
carbohydrate.
• This is why we store our spare energy as a layer of fat under the skin.
• This fat layer also keeps us warm, and provides padding against cold.
• Eating too much fat in the diet (especially fat from animal sources) can
cause heart disease, because it encourages layers of fat to clog up our
arteries.
• Enzyme that breakdown fats is lipase.
FOOD TESTS
FOOD NAME OF
No METHOD RESULT
TESTED TEST
Present: brown to
Add a few drops of iodine solution (brown) to a
1 Starch Starch test blue-black
solution of the food.
Absent: remains brown
Add an equal amount of Benedict’s
Glucose Present : blue to green or
Benedict’s solution/Reagent (light blue) to a solution of
2 (Reducing orange or brick red
test the food.
sugar) Absent: remains blue
Boil carefully.
Present: blue to violet /
Add Biuret solution/Reagent (light blue) to the
3 Protein Biuret test purple/ lilac
solution of food.
Absent: remains blue
Present : White emulsion
Emulsion Dissolve the food in ethanol. Pour the solution
4 Fats is formed
test into a clean test tube of water.
Absent: colorless solution
Take 2 cm3 of a 0.1% solution of DCPIP (a blue
Present: blue colour of
dye) in a test tube. Draw 2 cm3 of lemon juice in
5 Vitamin C DCPIP test DCPIP becomes colorless
a syringe. Add this juice drop by drop into the
Absent: remains Blue
test tube.
Starch test
Benedict’s test
Emulsion test
Nucleic acids
• Two types:
a. Deoxyribonucleic acid (DNA-double helix)
b. Ribonucleic acid (RNA-single strand)
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DNA is a very large molecule made up of a long chain of
sub-units.
The sub-units are called nucleotides.
Each nucleotide is made up of;
1. a pentose sugar called deoxyribose
2. a phosphate group -PO4 and
3. a Nitrogenous base
▪ There are four different Nitrogenous bases;
i. Adenine (A)
ii. Thymine (T)
iii. Guanine (G)
iv. Cytosine (C)
Structure of DNA
▪ DNA, or deoxyribonucleic acid, is the molecule that contains the 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.
All nucleotides contain the same phosphate and deoxyribose sugar, but differ
from each other in the nitrogenous base attached.
▪ 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)
• The phosphate and sugar section of the nucleotides form the ‘backbone’ of the
DNA strand (like the sides of a ladder) and the base pairs of each strand connect
to form the rungs of the ladder.
• It is this sequence of bases that holds the code for the formation of proteins.
FOOD SAMPLE TEST REAGENT USED COLOUR OBSERVED RESULT and CONCLUSION
A Starch Test Iodine
B Benedicts Test Benedicts Reagent
C Biuret Test Biurets Reagent
D Emulsion Test Ethanol
E Vitamin C Test DCPIP
