Biological Molecules
Biological molecules are made and used by all living organisms. They include Carbohydrates,
Proteins, Lipids, DNA, ATP, Water, and Inorganic Ions.
Monosaccharides:
Monosaccharides are carbohydrates which are an energy source and store as well as provide
structural support to the cell walls of plants. They include Glucose (alpha and beta), galactose and
fructose, these are isomers of each other. General formula of (CH2O)n, where n is any number
between 3 and 7.
Disaccharides:
Made through the condensation (formation of water) reactions between 2OH groups, on a
monosaccharide, to form a Glycosidic bond. Formula for the disaccharides below is C12H22O11. These
polymers are separated by hydrolysis (addition of water).
Formation of common disaccharides:
glucose + glucose = maltose
glucose + galactose = lactose
glucose + fructose = sucrose
Polysaccharides:
Long chains of monosaccharides joined by condensation reactions/glycosidic bonds. Examples
include Starch, Glycogen and Cellulose.
Starch Glycogen Cellulose
Energy store – Plants Energy store – Animals Structural support in cell wall
Alpha Glucose Beta Glucose
Respiration
Insoluble – no osmotic effect and can’t diffuse out of cell
Coiled – compact Straight chains
Branched – easily hydrolysed Unbranched – allows H bonds
Amylose – unbranched and Shorter chains than starch Many chains form a
coiled microfibril, with crosslinks
forming a macrofibril
Amylopectin – side branches More highly branched Prevents cell
shrinkage/bursting
Tests for:
Starch Reducing Sugar - Non-reducing sugar – first complete the test for
Benedict’s Test reducing sugars, if this is negative then follow
these steps.
2cm3 of sample into 2cm3 of sample into 2cm3 of sample into test tube
test tube test tube
2 drops of 2cm3 of Blue 2cm3 of dilute HCl, heat mixture for 5 minutes –
Orange/Brown Iodine Benedict’s reagent, this will hydrolyse any disaccharide
solution and shake heat mixture for 5
minutes
If blue/black colour Colour change from Slowly add Sodium Hydrogencarbonate
, appears then there is Green, Yellow, Orange solution, to neutralise the acid – use pH paper
starch to Brick Red. to check
Complete the test for reducing sugars again, if
positive then there were non-reducing sugars
Lipids:
Lipids contain Carbon, Hydrogen and Oxygen, they are insoluble in water, but soluble in organic
solvents (i.e. Alcohols and Acetone). There are 3 main types of lipid; Triglyceride, Phospholipid and
Cholesterol.
Lipids have many functions including energy storage (once oxidised they release twice as much
energy as carbohydrates), waterproofing (as they are insoluble, plants and insects have waxy layers
to conserve water), insulation (lipids are slow conductors of heat and acts as electrical insulators)
and protection (stored around delicate organs i.e. the kidney).
Triglycerides
3 fatty acids combined with one glycerol molecule, ester bonds join them together (COOC)
The differences between triglycerides comes from the R-groups, which can either be
saturated, mono-unsaturated or polyunsaturated
Low mass to energy ratio – good storage molecules
Insoluble as they are large, non-polar molecules – no osmotic effect
High ratio of H to O atoms – release water when oxidised
High ratio of energy storing C-H bonds – good energy source
Phospholipids
2 fatty acids, one glycerol molecule AND one phosphate group
Hydrophobic tail and Hydrophilic head
Polar molecule – position themselves differently when placed in water and form a bilayer
within CSMs
Phospholipid structure allows them to form Glycolipids by combing with carbohydrates at
CSM – used for cell recognition
Test for Lipids/Emulsion test
1. Use completely dry and grease free test tube
2. Use 2cm3 of the sample (in liquid form) and add 5cm3 of ethanol
3. Shake the tube thoroughly to dissolve any lipid in the sample
4. Add 5cm3 of water and shake
5. A cloudy-white colour indicates the presence of a lipid
6. Controls can be carried out using 2cm 3 of water instead of the sample, result should be no
colour change
Proteins – structure of an amino acid
AA are the basic monomer units which combine to form polypeptides, which combine to
form proteins
There are 100 identified AA, 20 of which are naturally occurring in proteins. These same 20
AA occur in all living organisms, which is evidence for evolution
Biological molecules are made and used by all living organisms. They include Carbohydrates,
Proteins, Lipids, DNA, ATP, Water, and Inorganic Ions.
Monosaccharides:
Monosaccharides are carbohydrates which are an energy source and store as well as provide
structural support to the cell walls of plants. They include Glucose (alpha and beta), galactose and
fructose, these are isomers of each other. General formula of (CH2O)n, where n is any number
between 3 and 7.
Disaccharides:
Made through the condensation (formation of water) reactions between 2OH groups, on a
monosaccharide, to form a Glycosidic bond. Formula for the disaccharides below is C12H22O11. These
polymers are separated by hydrolysis (addition of water).
Formation of common disaccharides:
glucose + glucose = maltose
glucose + galactose = lactose
glucose + fructose = sucrose
Polysaccharides:
Long chains of monosaccharides joined by condensation reactions/glycosidic bonds. Examples
include Starch, Glycogen and Cellulose.
Starch Glycogen Cellulose
Energy store – Plants Energy store – Animals Structural support in cell wall
Alpha Glucose Beta Glucose
Respiration
Insoluble – no osmotic effect and can’t diffuse out of cell
Coiled – compact Straight chains
Branched – easily hydrolysed Unbranched – allows H bonds
Amylose – unbranched and Shorter chains than starch Many chains form a
coiled microfibril, with crosslinks
forming a macrofibril
Amylopectin – side branches More highly branched Prevents cell
shrinkage/bursting
Tests for:
Starch Reducing Sugar - Non-reducing sugar – first complete the test for
Benedict’s Test reducing sugars, if this is negative then follow
these steps.
2cm3 of sample into 2cm3 of sample into 2cm3 of sample into test tube
test tube test tube
2 drops of 2cm3 of Blue 2cm3 of dilute HCl, heat mixture for 5 minutes –
Orange/Brown Iodine Benedict’s reagent, this will hydrolyse any disaccharide
solution and shake heat mixture for 5
minutes
If blue/black colour Colour change from Slowly add Sodium Hydrogencarbonate
, appears then there is Green, Yellow, Orange solution, to neutralise the acid – use pH paper
starch to Brick Red. to check
Complete the test for reducing sugars again, if
positive then there were non-reducing sugars
Lipids:
Lipids contain Carbon, Hydrogen and Oxygen, they are insoluble in water, but soluble in organic
solvents (i.e. Alcohols and Acetone). There are 3 main types of lipid; Triglyceride, Phospholipid and
Cholesterol.
Lipids have many functions including energy storage (once oxidised they release twice as much
energy as carbohydrates), waterproofing (as they are insoluble, plants and insects have waxy layers
to conserve water), insulation (lipids are slow conductors of heat and acts as electrical insulators)
and protection (stored around delicate organs i.e. the kidney).
Triglycerides
3 fatty acids combined with one glycerol molecule, ester bonds join them together (COOC)
The differences between triglycerides comes from the R-groups, which can either be
saturated, mono-unsaturated or polyunsaturated
Low mass to energy ratio – good storage molecules
Insoluble as they are large, non-polar molecules – no osmotic effect
High ratio of H to O atoms – release water when oxidised
High ratio of energy storing C-H bonds – good energy source
Phospholipids
2 fatty acids, one glycerol molecule AND one phosphate group
Hydrophobic tail and Hydrophilic head
Polar molecule – position themselves differently when placed in water and form a bilayer
within CSMs
Phospholipid structure allows them to form Glycolipids by combing with carbohydrates at
CSM – used for cell recognition
Test for Lipids/Emulsion test
1. Use completely dry and grease free test tube
2. Use 2cm3 of the sample (in liquid form) and add 5cm3 of ethanol
3. Shake the tube thoroughly to dissolve any lipid in the sample
4. Add 5cm3 of water and shake
5. A cloudy-white colour indicates the presence of a lipid
6. Controls can be carried out using 2cm 3 of water instead of the sample, result should be no
colour change
Proteins – structure of an amino acid
AA are the basic monomer units which combine to form polypeptides, which combine to
form proteins
There are 100 identified AA, 20 of which are naturally occurring in proteins. These same 20
AA occur in all living organisms, which is evidence for evolution
