Biological Molecules (organic molecules: in organisms, Carbon and Hydrogen
Atoms)
Provide Energy (or/and)
Raw materials for growth and repair
Macro Nutrients: carbohydrates, fats and oils, and proteins
Micronutrients: vitamins and minerals
4 main MOLECULE groups: Carbohydrates, Lipids, Proteins and Nucleic Acids
Large Molecules: contain subunits/monomers:
Can be split by HYDROLYSIS: which uses up Water.
Joined Again by CONDENSATION, gives out Water.
Use: specific organism can utilize/rearrange the molecule based on its metabolic
requirement. Eg, in animals, starch from cereals/corn/plant is converted into glucose
by hydrolysis and used up, and remaining is stored as glycogen by condensation.
I. Carbohydrates
Carbohydrates are compounds of:
carbon, C
hydrogen, H
oxygen, O.
One of the simplest carbohydrates is glucose, a simple sugar.
Some carbohydrate molecules (like the sugar we normally eat) consist of two simple sugar
molecules chemically joined together. (SUCROSE)
Larger carbohydrate molecules like cellulose, starch and glycogen are made from many
glucose molecules joined together.
Monosachharides (simplest carbohydrates_Monomer): Glucose (C6H12O6) (plants &
fruits), Fructose (sweet fruit & Honey), Galactose (milk), Ribose (DNA/RNA) (main
source of energy for many cells.) (Soluble)
Disaccharides: Sucrose (fructose+glucose), Maltose (2 glucose), Lactose
(glucose+galactose) (Soluble)
Polysaccharides: cellulose, Starch and glycogen (insoluble, stores energy, and some
form important structures, eg. Cell wall- cellulose)
Name Function Source Made up of
starch energy and nutrient Plants: chloroplasts and cytoplasm in plant Glucose Monomers
storage cells
cellulose structural support Plant: cell walls Glucose Monomers
glycogen energy and nutrient Animals: liver and muscles Glucose Monomers
storage
II. Fats and Oils (LIPIDS):
Can be,
Saturated: single bonds between carbon atoms, mainly solid in room temperature OR
Unsaturated: one or more bonds between carbon atoms, mainly liquid in room
temperature
(INSOLUBLE:
excellent stores of energy,
provide structural support for the cells,
and help in cell signaling,
hormones (steroid)
and because of non-polarity nature do not interact with water and form barrier
between watery environments (water proofing and buoyancy)
thermal Insulation
electrical insulation of nerves
mechanical protection
Like carbohydrates, fats and oils are compounds of:
carbon, C
hydrogen, H
oxygen, O. (less O2 than in carbohydrates)
Fats and oils are very similar chemically, but fats are in the solid state at room
temperature whereas oils are in the liquid state.
Fats tend to be found in animals, while oils tend to be found in plants.
substances are made from 2 smaller molecules, 1 glycerol and 3 fatty acids (monomers).
A molecule of a fat or oil is formed by the reaction of one glycerol (Product of the
breakdown of fats that can be converted back to glucose by mechanisms in the liver and
kidneys) molecule with three fatty acid molecules.
Depending on the fat or oil, the three fatty acid molecules can be the same or different.
Main types: Triglycerides, Phospholipids, Steroids and waxes
III. Proteins:
1. Proteins are very large molecules made from smaller molecules called Amino Acids
(AA) (monomer)
2. (long Chain of AA)
3. (sequence of AA: Shape of protein which determines function: Eg, Keratin : thin,
found in hair)
4. (SOLUBLE: easily transported, takes part in reactions)
Like carbohydrates, fats and oils, proteins contain:
carbon, C
hydrogen, H
oxygen, O.
However, all proteins also contain nitrogen atoms, N. Some proteins may also contain very
small amounts of sulfur and selenium.
Functions of Proteins: Examples:
Hemoglobin_red pigment: in Red Blood Cells in blood, transports O2 to body parts
Other examples are in the below box.
Amino acids
There are over 20 naturally occurring types of amino acids.
Each molecule contains two reactive groups of atoms that allow amino acids to join end to
end.
The very long molecules produced by this process are proteins.
IV. Nucleic Acids: DNA, RNA
DNA: (deoxyribonucleic acid) is the genetic material in living cells. Nearly every cell in your
body has a complete copy of all of your DNA
RNA: (ribonucleic acid)
DNA consists of two strands that coil together to form a double helix (two spirals that wrap
around each other).
Each strand contains three main chemicals: phosphates, sugars called deoxyribose and
nitrogen-containing bases (A,C,T,G: adenine, thymine, cytosine and guanine). small units
that form DNA, containing a phosphate, a sugar and a base, are known as nucleotides
(monomer).
The phosphates and sugars form the backbone of the strands, while the bases are located in
the center of the molecule and these pairs of bases, A with T and C with G, form the cross
links between the strands.
Practical: Testing for biological molecules (for LIPIDS: Physical reaction,
Others are Chemical Reaction)
oxidation is gain of oxygen or loss of electrons
reduction is loss of oxygen or gain of electrons.
In a chemical reaction involving these processes, one substance is oxidised while another is
reduced. Some carbohydrates are described as reducing sugars. They can cause the reduction of
other substances (and become oxidised during this process). Glucose is an example of a reducing
sugar.
1. Benedicts test: For Sugars
The range of colours can make this test semi-
quantitative, in that the more the colour changes, the more of the Benedict’s solution has
reacted and the more reducing sugar was present in the original sample.
2. Iodine Test: For Starch
Negative (orange-brown) and Positive (blue-black) iodine tests for starch.
3. Test for Fats: Ethanol Emulsion Test
positive (white/milky
colour) ethanol emulsion test for a fat or oil. The negative result will show no colour change.
If fat or oil is present, when the solution of food sample and ethanol is added to water it will
create a white or milky cloud emulsion.
Fats and oils are less dense than water, so if it is left to settle you may see a layer of oil or fat
on the surface.
Emulsion test is a Physical test, as lipid is insoluble in water.
4. Biuret Test: For Proteins: Detects Peptide Bonds
Negative (blue or No colour cahnge) and positive (violet/lilac) biuret tests for proteins.
5. Test for Vitamin C: DCPIP
The DCPIP (dichlorophenolindophenol) test for vitamin C. A positive result for vitamin C is a
change of colour of DCPIP from blue to colourless. If the blue colour remains, there is no
vitamin C.
If a large amount of vitamin C is present, the blue colour may disappear permanently from the
liquid DCPIP. If only a small amount of vitamin C is present, the blue colour may disappear
slightly from the liquid that is in contact with the food sample.
Few Drops of food sample into DCPIP and positive result infers strong Vit C concentration,
and vice versa. Number of drops of vitamin C required to have a positive result determines
how strong is the Vit C concentration in the food sample.
PS: Question 2 in Text Book: Page 30
