SPECIFICATION
(c) Biological molecules
Students should:
2.7 identify the chemical elements present in carbohydrates, proteins
and lipids (fats and oils)
2.8 describe the structure of carbohydrates, proteins and lipids as
large molecules made up from smaller basic units: starch and
glycogen from simple sugars, protein from amino acids, and lipid
from fatty acids and glycerol
2.9 practical: investigate food samples for the presence of glucose,
starch, protein and fat
The most common molecules in living things;
Water
BUT water is NOT a biological molecule.
Carbohydrates
Proteins
Biological molecules
Lipids
Nucleic acids
Elements that make up biological molecules:
C, H, O, N, S
Carbohydrates contain 3 elements; C, H, O
Lipids contain 3 elements; C, H, O
Proteins contain 4 or 5 elements; C, H, O, N, S
•
•
All biological molecules are huge. So, we call them
Macromolecules.
They are made of small molecules (same type or
different types) joining together. So, we call them
Polymers.
A polymer is a
large molecule
made up of a long
chain of repeating
subunits called
monomers
PMG Biology
• Protein
• Starch
• Cellulose
• Glycogen
Amino
acid
glucose
Basic unit/
monomer
Glycerol +
fatty acid
• Lipids
nucleotide
• Nucleic
acid
Carbohydrates
STRUCTURE OF CARBOHYDRATES
Simplest carbohydrates comprise a single molecule
and are called monosaccharides.
Trioses
(3-carbons)
Pentoses
(5-carbons)
Hexoses
(6-carbons)
A disaccharide is formed when two monosaccharides
join together by a covalent bond.
Polysaccharides are polymers composed of a large
number of monosaccharides.
Monosaccharides
Carbohydrates
Mono= one
Di= two
Poly= many
Disaccharides
Polysaccharides
Glucose
Maltose
Starch
Fructose
Sucrose
Glycogen
Galactose
Lactose
Cellulose
FUNCTIONS OF CARBOHYDRATES
2. Form the cell wall of
A2B Car Rental
Plants: Cellulose
Fungi: Chitin
Bacteria: Peptidoglycan
Expii
1. Glucose is the
primary fuel in cells
Glycogen in the
liver and muscles
of animals
3. Storage of
readily available
energy
Starch in plants
GLUCOSE
Glucose
is a
Monosaccharide
&
Chemical formula
C6H12O6
Structure of glucose
YES, all three
polysaccharides you
learn are made of
glucose molecules
joining together by
covalent bonds.
Starch
Glycogen
Cellulose
Researchgate.net
Food rich in carbohydrates
Protein
STRUCTURE OF PROTEIN
Basic unit is
Amino acid
teaching.ncl.ac.uk
20 different amino acids
exist naturally in
organisms
Polypeptide chain
Amino acids join together by
Peptide bonds
Working protein
peptide bonds and form
polypeptide chains.
Polypeptide chain can fold
to form a 3-D structure to
become a functional protein.
FUNCTIONS OF PROTEIN
Innerzyme
FUNCTIONS OF PROTEIN
Role
Examples
Functions
Digestive enzyme
Amylase, lipase, pepsin
Break down nutrients in
food into small pieces that
can be readily absorbed
Transport
Hemoglobin
Carry oxygen through out
the body in blood
Structure
Actin, keratin
Build different structures,
like muscles, hair
Hormone signaling
Insulin, glucagon
Coordinate the activity of
different body systems
Defense
Antibodies
Protect the body from
foreign pathogens
Storage
Legume storage proteins,
egg white (albumin)
Provide food for the early
development of the embryo
or the seedling
Food rich in protein
Lipids
LIPIDS (FAT AND OIL)
Fat
Oil
heart.org
• solid at room temperature
• from animal sources
betterhealth.vic.gov.au
• liquid at room temperature
• from plant sources
STRUCTURE OF LIPIDS:
Lipids are made of two parts:
1. Glycerol back bone
2. One or more hydrocarbon
chains called fatty acids
We can draw a
simple lipid molecule
as shown below.
Unlike carbohydrates,
lipids have much less
oxygen
OpenStax Biology.
FUNCTIONS OF LIPIDS
1. Fat depots
under the
skin and
around
organs act as
a long-term
store of
energy
https://www.nature.com/articles/emm20165
2. Cushion vital organs from
mechanical damage (e.g. brain,
kidneys, heart, liver)
FUNCTIONS OF LIPIDS
Form the cell
membrane of
cells.
Wikimedia Commons
By Sodini Ariyarathna
Fat layer under
the skin acts as
thermal
insulation
Food rich in lipids
Tests to identify
biological molecules
(Food tests)
TEST FOR GLUCOSE
Benedict’s test
1. Add equal volume of Benedict’s solution to the 5ml of the sample solution.
2. Heat the mixture in a water bath.
3. The colour of the solution changes to ORANGE/ BRICK RED if glucose is
present.
sciencephoto.com
BIology Revision Site - Weebly
Safety measures:
1. Use goggles & gloves
2. Use a water bath
Benedict’s
solution
Glucose
TEST FOR STARCH
Iodine test
1. Add one or two drops of Iodine solution (yellow) to the sample (solution
or a solid).
2. Iodine turns to BLUE BLACK colour in the presence of starch.
https://fineartamerica.com
Safety measures:
1. Use goggles & gloves
TEST FOR PROTEIN
Biuret test
Method 1:
1. Add 1ml of Biuret reagent into
1ml of aqueous food sample.
2. Mix well.
Method 2:
1. Add 1ml of dilute KOH/NaOH
into 1ml of aqueous food sample.
2. Mix well.
3. Add 1% of CuSO4
Observation:
The colour of the solution changes to
PURPLE if protein is present
http://birdingpark.blogspot.com
Safety measures:
1. Use goggles &
gloves
TEST FOR LIPIDS
Ethanol emulsion test
1. Add a few drops of the liquid food sample to a dry test tube.
2. Add 2cm3 of ethanol and shake it vigorously.
3. Add the mixture into a test tube containing ¾ of distilled water.
Observation:
A white cloudy emulsion is
formed if lipids are present.
TACtivities
Safety measures:
1. Use goggles & gloves
FOOD TESTS SUMMARY
Food sample
Reagent
Glucose
Benedict’s
Starch
Iodine
Protein
Fat & oil
Method
Initial colour
Add Benedict’s
reagent to the
Blue
food and boil in
a water bath.
Add iodine
reagent to the Yellow-brown
food.
Biuret (a
mixture of
Add Biuret
potassium
reagent to the Blue
hydroxide and food.
copper sulfate).
Add ethanol to
the food to
Ethanol
dissolve the fat Colourless
then add
water.
Colour of
positive
result
Brick red
precipitate
Blue-black
Lilac/purple
White
emulsion
THANK YOU
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