Biological
Molecules
Food Tests
 Benedicts
Test-(Reducing Sugars)
 Biuret Test-(Protein)
 Iodine test-(Starch)
 Emulsion test(Lipids)
 Non-reducing sugars test
Benedict’s Test
Add 2cm3 of the sugar solution to a testtube, and then an equal volume of
Benedict’s solution. Bring to the boil in a
water-bath.
Result: Turns green, then yellowish,
then may form brick-red precipitate.
Basis: The Cu++ ions in the copper
sulphate in Benedict’s are reduced by
the sugar to insoluble Cu+ which
precipitates out
Biuret Test
Add equal quantities of test solution and
potassium hydroxide and mix. Add two
drops of copper sulphate, and mix
Result: Mauve or purple colour slowly
develops
Basis: Nitrogen atoms in the peptide
chain form a purple complex with the
Cu++ ions
Iodine Test
Add a few drops of potassium iodide
solution to the test solution and mix
A blue/black colouration develops
A polyiodide complex forms with the
starch molecules
Emulsion test
Add equal quantities of the suspected
lipid and absolute ethanol in a test tube.
Shake vigorously to dissolve. Add an
equal quantity of cold water.
Result: A cloudy white suspension
Lipids are insoluble in water, so
adding water to a solution of the lipid
in alcohol results in an emulsion of
tiny lipid droplets in the water which
look white as they reflect light.
Non Reducing Sugars
Add 2cm3 sucrose solution to a testtube. Add 1cm3 dilute sulphuric acid. Boil
for one minute, and then carefully
neutralize with sodium bicarbonate. (take
care, as it will effervesce). Carry out
Benedict’s test
The acid hydrolyses the sucrose (breaks
the glycosidic bond) making two
monomer molecules (glucose and
fructose), which are reducing sugars
– building blocks of biological
molecules
 Polymer - a chemical compound
consisting of repeating structural units
(monomers)
 Macromolecules – another name for a
polymer
 Monomer
Carbohydrates


Made of C, H and O
Three types:
1. Monosaccharide
2. Disaccharide
3. Polysaccharide
Monosaccharides
 Simplest
carbohydrates
 Glucose, fructose, galactose
Glucose
 Two
types:
Glycosidic Bonds
Condensation
Hydrolysis
Polysaccharides
Starch
Storage polysaccharide in plants
Made of two substances:


1.
2.
Amylose
Amylopectin
Amylose
α glucose molecules
with 1-4 links
 Coils into a spiral
 Held together with
hydrogen bonds

Amylopectin
α glucose with 1-4
links and 1-6 links
 Causes branching
chains

Glycogen

Storage in animals
and fungi
 α glucose molecules
with 1-4 links and 1-6
links
 Forms a branching
chain
 Held together with
hydrogen bonds
Cellulose
β glucose with 1-4 links
 Adjacent molecules in the chain are flipped 180
degrees
 Hydrogen bonds form between different chains
forming a bundle of microfibrils

Proteins
Primary Structure
 Monomer
 Amino
– amino acid
acids joined by peptide bonds
 Condensation reaction
Secondary Structure
 Two


possible structures:
α helix
β pleated sheet
 Held
together by hydrogen bonds
Tertiary Structure
 Secondary
structure folded and bonds
form between the R chains
 Different types of bonds:




Hydrogen bonds
Ionic bonds
Disulphide bridges
Hydrophobic interactions
Tertiary Structure Bonds
Quaternary structure
 More
than one tertiary structure joined
together.
Haemoglobin
 Globular
protein
 4 tertiary structures joined together
 Two alpha chains (141 aa), and two beta
chains (146 aa)
 Each chain has a haem (containing an iron
atom) group attached
 This is used to bond the oxygen
Haemoglobin
The “R” groups on amino acids are
sometimes referred to as side chains.
Some amino acids have hydrophobic side
chains (repelling water), and some have
hydrophilic side chains (attracting water)
Haemoglobin
Haem
Haemoglobin
On the four polypeptide chains that make
up the haemoglobin, amino acids with
hydrophobic side chains point inwards,
helping to hold the molecule together
Amino acids with hydrophilic side
chains point outwards, making the
haemoglobin molecule soluble.
Collagen
 Fibrous
protein
 Three strands plaited together
 Very strong
Lipids
 Made


of two parts:
Glycerol
Three fatty acid chains
 High
energy due to many hydrogen atoms
Saturated and unsaturated
 Saturated
fats have no carbon to carbon
double bonds, they are solid at room
temperature
 Unsaturated fats have one or more carbon
to carbon double bonds. These form kinks
in the fatty acid chains and so they are
liquids at room temperature.
Phospholipids

Polar region is the
phosphate group and
it allow it to be soluble
in water – hydrophillic
 The non-polar fatty
acid chains are
insoluble in water hydrophobic
Structure and function
 Their
insulating properties keep mammals
warm.
 They contain twice the stored energy of
carbohydrates, gram for gram.
 They are used in the formation of cellsurface membranes.
 In aquatic mammals, the fat is less dense
than water, so it acts as a buoyancy aid.
Water
Properties of water
 High
specific heat capacity
 High heat of vaporisation


both of which are a result of the
extensive hydrogen bonding between its
molecules.
These two unusual properties allow water to
moderate Earth's climate by buffering large
fluctuations in temperature.
approximately 4 °C pure water reaches
its maximum density
 at

Protects aquatic environments
 Universal
solvent
 Water molecules stay close to each other
(cohesion), due to the collective action of
hydrogen bonds between water
molecules. Leading to high surface
tension.
 Water also has high adhesion properties
because of its polar nature.
Essay
a)
b)
Describe the characteristics of water.
How do these characteristics enable
living organisms to survive.