BIOLOGICAL MOLECULES
Chapter 4
LEARNING
OBJECTIVES
made up of
C, H, O
Monomers [single unit]
Monosaccharides
CARBOHYDRATES
Polymers /
Macromolecules
Disaccharides and
polysaccharides
Carbohydrates
Simple sugars Complex sugars
Monosaccharides Disaccharides Polysaccharides - made up of
many, many glucose molecules
E.g.
Sucrose = glucose + fructose E.g. Starch, Cellulose,
E.g. Glucose, Fructose Glycogen
Maltose = glucose + glucose
Lactose = glucose + galactose
(JUST FYI)
Polysaccharides
Plants Animals
Starch Glycogen
storage storage
Cellulose
structural (cell wall)
FUNCTIONS OF CARBOHYDRATES
Glucose: Used to provide [give] energy from respiration
Sucrose: plants convert [change] glucose into sucrose for transport in the phloem
tissue [from leaves to various organs].
Cellulose: used to make the tough cell walls, which maintain the shape of plant cells.
Starch: plants store glucose in the form of starch in seeds, tubers (potato, tapioca,
colocasia), etc.
Glycogen: animals store glucose as glycogen in the liver and muscles.
Made up of
C, H, O
Monomers [single unit]
Glycerol & Fatty acids
LIPIDS
Polymers /
Macromolecules
Fats and Oils
Structure of a Fat Molecule
FUNCTIONS OF FATS
Reserve store of energy - to be released when carbohydrates have been used up.
Insulation - Adipose tissues [under the skin and around some organs] have cells which
store fats / oils. These tissues help keep the body warm by [retain body heat].
E.g blubber in walruses, whales etc.
Plants store oils in seeds [peanut, coconut, sunflower] to provide energy for
germination.
made up of
C, H, O, N, [P/S]
Monomers [single unit]
Amino acids
Polymers / PROTEINS
Macromolecules
Peptides and
polypeptides
FUNCTIONS OF PROTEINS
Needed for growth, for making new cells and repairing
damaged tissues.
Antibodies (immunity), enzymes (digestion, respiration),
haemoglobin (oxygen transport), keratin (toughness of skin, nails
and hair) are all proteins.
STRETCH YOURSELF…
What is the simple sugar found in fruits?
What element is present in proteins that is not present in carbohydrates and fats?
What’s the difference between fats and oils?
made up of
C, H, O, N, P
Monomers [single unit]
Nucleotides
Polymers /
NUCLEIC ACIDS
Macromolecules
DNA, RNA
THE DOUBLE
HELIX “LADDER”
STRUCTURE OF DNA
• DNA has two strands coiled together to form a double helix.
• On each strand, contains chemicals called nitrogenous bases.
• There are 4 types of bases in DNA [A, T, G,C]
• Hydrogen bonds are formed between pairs of bases. This holds the
two strands together.
• The bases always pair up in the same way: A with T, and G with C.
Note (not to be written in exam):
• When unwound, this coil looks a bit like a ladder.
• The sugar and phosphate backbone form the two “side rails”.
the “rungs” of the ladder are made up of the bases.
Full names of A, T, G, C are not required
SPECIFIC BASE PAIRING
A always pairs up with T
C always pairs up with G
FUNCTIONS OF DNA
•Genetic material – chemical that makes up genes and
chromosomes.
•DNA base sequence determines amino acid sequences in
proteins.
•This determines the function and development of cells, tissues,
organs etc.
•This determines characteristics of all living organisms.
•Unit of inheritance.
Tests for:
• Starch
FOOD TESTS • Reducing sugars
• Proteins
Always asked in paper 6
• Fats/oils
• Vitamin C
STARCH - IODINE TEST
PROCEDURE
A few drops of iodine solution added to sample /
extract* / solution.
Note – iodine solution ≠ iodine
Iodine solution
Colour changes to blue-
black if starch is present.
Samples with a higher starch
content will give a darker
colour.
A colorimeter can be used
to give a quantifiable
difference in colour densities.
OBSERVATION AND
RESULTS
REDUCING SUGARS - BENEDICT’S TEST
PROCEDURE
Benedict’s solution [blue] + solution / extract*.
Heat in a water bath at 85 0C.
Note – this is the only test that requires heat.
OBSERVATION AND RESULTS
If reducing sugars present, the solution will change colour: blue –
green – yellow –brick red ppt.
More sugar – faster colour change / deeper red ppt.
A colorimeter can be used to give a quantifiable difference in colour
densities.
Stretch your brain:
Can you see a pattern in the colour changes?
SEMI-QUANTITATIVE TEST
(Values just FYI)
PROTEINS -
BIURET TEST
PROCEDURE
Sample solution / extract* + Biuret solution
OBSERVATION AND
RESULTS
Colour change to lilac / purple indicates presence
of proteins.
Darker colour – indicates greater concentration of
protein in the sample.
A colorimeter can be used to give a quantifiable
difference in colour densities.
Remember – Biuret, sounds like violet
FATS & OILS -
ETHANOL TEST
TWO STEP PROCESS
Step 1 - Add ethanol to extract* / solution till a
clear solution is obtained [fats will dissolve in
ethanol].
Step 2 - Add water – fats are insoluble and a milky
white emulsion of fat droplets will form in the
ethanol – water mixture.
BASIC PRINCIPLE
Lipids do not mix with water But lipids and alcohol do!
VITAMIN C -
DCPIP TEST
PROCEDURE
Sample solution
/ extract* + DCPIP solution
Place 1 cm3 of DCPIP
solution in a test tube, add a
small amount of food sample (as
a solution).
OBSERVATION AND
RESULTS
DCPIP is a blue coloured dye.
A positive test will show the blue colour of the dye disappearing.
If the Vitamin C solution is highly concentrated it will take only few drops to remove the colour. If the
vitamin C solution is weakly concentrated then many drops are needed to remove the colour.
A negative test shows a persistence of the blue colour.
Margin notes - Semi-quantitative tests – Tests that not only tell you the presence/absence of a substance,
but also how much of the substance there is in that sample.
