Topic 1: Biological Molecules
BIOLOGICAL MOLECULES
MONOMERS AND POLYMERS:
● monomers - small, basic molecular units that can form a polymer
● polymers - large, complex molecules made from long monomer chains joined
together
● condensation reactions - forms a chemical bond between two monomers, releasing a
molecule of water
● hydrolysis - breaks the chemical bond between two monomers, using a water
molecule
CARBOHYDRATES:
monosaccharides - a single sugar molecule
● condensation reactions between monosaccharides form a 1-4 glycosidic bond
● soluble in water because they have many hydroxyl groups which can form hydrogen
bonds with water molecules
glucose
● hexose sugar
● has two isomers, alpha and beta glucose: in alpha glucose, the hydroxyl group of
carbon 1 points below the plane of the ring; whilst in beta glucose, the hydroxyl group
of carbon 1 points above the plane of the ring
disaccharides - formed by the condensation of two monosaccharides
key reactions:
glucose + glucose = maltose
glucose + fructose = sucrose
glucose + galactose = lactose
testing for reducing sugars:
, reducing sugars can donate electrons to another molecule
● place 3cm^3 of food solution into a boiling tube, add 3cm^3 of Benedict’s reagent
● place the boiling tube into a beaker of gently boiling water, leave for 5 minutes
● reducing sugars are present if the mixture turns green, yellow, orange or brick-red
● none are present if the mixture remains blue
testing for non-reducing sugars:
● carry out Benedict’s reaction with the sample to check that it is not a reducing sugar
● add 2cm^3 of a fresh sample, along with 2cm^3 of hydrochloric acid into a boiling
tube
● place the test tube in gently boiling water for 5 minutes (HCl will hydrolyse
disaccharides into their monosaccharides)
● add 2cm^3 of sodium hydrogencarbonate to neutralise the acid
● add Benedict’s reagent and heat in gently boiling water for 5 minutes, watch for a
orange-red precipitate which indicates a positive test
polysaccharides - 3 or more monosaccharides chemically joined, insoluble and very large
starch
consists of two molecules: amylose and amylopectin
starch is insoluble, does not affect water potential
amylose and amylopectin are polymers, too large to diffuse out of cells
amylose:
● long, unbranched chains of alpha glucose
● angle of the 1-4 glycosidic bonds create a helical structure, which make it compact
and ideal for storage
amylopectin:
● polymer of alpha glucose joined by 1-4 glycosidic bonds
● long, branched chains allow the enzymes that hydrolyse the molecule to access the
glycosidic bonds easily, so glucose is released easily
test:
● iodine turns from yellow to blue-black when in contact with starch
glycogen
● polymer of alpha glucose, shorter chains and more highly branched
● highly branched - compact and ideal for storage
BIOLOGICAL MOLECULES
MONOMERS AND POLYMERS:
● monomers - small, basic molecular units that can form a polymer
● polymers - large, complex molecules made from long monomer chains joined
together
● condensation reactions - forms a chemical bond between two monomers, releasing a
molecule of water
● hydrolysis - breaks the chemical bond between two monomers, using a water
molecule
CARBOHYDRATES:
monosaccharides - a single sugar molecule
● condensation reactions between monosaccharides form a 1-4 glycosidic bond
● soluble in water because they have many hydroxyl groups which can form hydrogen
bonds with water molecules
glucose
● hexose sugar
● has two isomers, alpha and beta glucose: in alpha glucose, the hydroxyl group of
carbon 1 points below the plane of the ring; whilst in beta glucose, the hydroxyl group
of carbon 1 points above the plane of the ring
disaccharides - formed by the condensation of two monosaccharides
key reactions:
glucose + glucose = maltose
glucose + fructose = sucrose
glucose + galactose = lactose
testing for reducing sugars:
, reducing sugars can donate electrons to another molecule
● place 3cm^3 of food solution into a boiling tube, add 3cm^3 of Benedict’s reagent
● place the boiling tube into a beaker of gently boiling water, leave for 5 minutes
● reducing sugars are present if the mixture turns green, yellow, orange or brick-red
● none are present if the mixture remains blue
testing for non-reducing sugars:
● carry out Benedict’s reaction with the sample to check that it is not a reducing sugar
● add 2cm^3 of a fresh sample, along with 2cm^3 of hydrochloric acid into a boiling
tube
● place the test tube in gently boiling water for 5 minutes (HCl will hydrolyse
disaccharides into their monosaccharides)
● add 2cm^3 of sodium hydrogencarbonate to neutralise the acid
● add Benedict’s reagent and heat in gently boiling water for 5 minutes, watch for a
orange-red precipitate which indicates a positive test
polysaccharides - 3 or more monosaccharides chemically joined, insoluble and very large
starch
consists of two molecules: amylose and amylopectin
starch is insoluble, does not affect water potential
amylose and amylopectin are polymers, too large to diffuse out of cells
amylose:
● long, unbranched chains of alpha glucose
● angle of the 1-4 glycosidic bonds create a helical structure, which make it compact
and ideal for storage
amylopectin:
● polymer of alpha glucose joined by 1-4 glycosidic bonds
● long, branched chains allow the enzymes that hydrolyse the molecule to access the
glycosidic bonds easily, so glucose is released easily
test:
● iodine turns from yellow to blue-black when in contact with starch
glycogen
● polymer of alpha glucose, shorter chains and more highly branched
● highly branched - compact and ideal for storage
