3.1.1 Monomers and polymers
22 December 2020 11:42
The variety of life, both past and present, is extensive, but the biochemical
basis of life is similar for all living things.
Monomers are the smaller units from which larger molecules are made.
Polymers are molecules made from a large number of monomers joined
together.
Monosaccharides, amino acids and nucleotides are examples of monomers.
A condensation reaction joins two molecules together with the formation of a
chemical bond and involves the elimination of a molecule of water.
A hydrolysis reaction breaks a chemical bond between two molecules and
involves the use of a water molecule
Biological molecules Page 1
,3.1.2 Carbohydrates
22 December 2020 11:43
Monosaccharides are the monomers from which larger carbohydrates are
made. Glucose, galactose and fructose are common monosaccharides.*
*These are typically sweet tasting, soluble substances which have the general formula (CH2O)n
A condensation reaction between two monosaccharides forms a glycosidic
bond.
Disaccharides are formed by the condensation of two monosaccharides:
• maltose is a disaccharide formed by condensation of two glucose
molecules*
*Maltose is formed by a condensation reaction between two alpha glucose
molecules, in which a hydroxyl group is removed from one glucose and a
hydrogen is removed from the other glucose to form a glycosidic bond and
water is released.
• sucrose is a disaccharide formed by condensation of a glucose molecule and
a fructose molecule (non-reducing sugar)
• lactose is a disaccharide formed by condensation of a glucose molecule and
a galactose molecule.
Glucose has two isomers, α-glucose and β-glucose, with structures:
Biological molecules Page 2
, Polysaccharides are formed by the condensation of many glucose units.
• Glycogen and starch are formed by the condensation of α-glucose.
• Cellulose is formed by the condensation of β-glucose.
The basic structure and functions of glycogen, starch and cellulose.
The relationship of structure to function of these substances in animal cells
and plant cells.
- Glycogen
Glycogen is the main energy storage molecule in animals.
Polysaccharide of alpha glucose joined together by 1, 4 and 1, 6 glycosidic bonds.
It is branched meaning that energy can be released quickly as enzymes can act simultaneously on
these branches.
It is coiled so it is a compact molecule thus maximising the amount of energy it can store
It is insoluble meaning it will not affect the water potential* of cells and cannot diffuse out of cells.
- Starch
Starch stores energy in plants and is a mixture of two polysaccharides:
Hydrolysed to maltose by amylase
Maltose hydrolysed to glucose by maltase
• Amylose :
- an unbranched chain of glucose molecules joined by 1, 4 glycosidic bonds, and as a result amylose is
coiled and thus a very compact molecule storing a lot of energy
- Hydrolyses to amylose, to maltose, to alpha glucose used in respiration
• Amylopectin :
- Amylopectin is branched and is made up of glucose molecules joined by 1, 4 and 1, 6 glycosidic
bonds. Due to the presence of many side branches these can be acted upon simultaneously by many
enzymes and thus broken down to release its energy.
- Cellulose
Cellulose is a component of cells wells in plants and is composed of long, unbranched chains of beta
glucose which are joined by glycosidic bonds.
These long chains of beta glucose form hydrogen bonds between each other forming microfibrils,
strengthening cellulose.
Cellulose is important in stopping the cell wall from bursting under osmotic pressure. This is because
it exerts inward pressure that stops the influx of water. This means that cells stay turgid and rigid,
helping to maximise the surface area of plants for photosynthesis.
*where salt goes, water will follow
Biological molecules Page 3
22 December 2020 11:42
The variety of life, both past and present, is extensive, but the biochemical
basis of life is similar for all living things.
Monomers are the smaller units from which larger molecules are made.
Polymers are molecules made from a large number of monomers joined
together.
Monosaccharides, amino acids and nucleotides are examples of monomers.
A condensation reaction joins two molecules together with the formation of a
chemical bond and involves the elimination of a molecule of water.
A hydrolysis reaction breaks a chemical bond between two molecules and
involves the use of a water molecule
Biological molecules Page 1
,3.1.2 Carbohydrates
22 December 2020 11:43
Monosaccharides are the monomers from which larger carbohydrates are
made. Glucose, galactose and fructose are common monosaccharides.*
*These are typically sweet tasting, soluble substances which have the general formula (CH2O)n
A condensation reaction between two monosaccharides forms a glycosidic
bond.
Disaccharides are formed by the condensation of two monosaccharides:
• maltose is a disaccharide formed by condensation of two glucose
molecules*
*Maltose is formed by a condensation reaction between two alpha glucose
molecules, in which a hydroxyl group is removed from one glucose and a
hydrogen is removed from the other glucose to form a glycosidic bond and
water is released.
• sucrose is a disaccharide formed by condensation of a glucose molecule and
a fructose molecule (non-reducing sugar)
• lactose is a disaccharide formed by condensation of a glucose molecule and
a galactose molecule.
Glucose has two isomers, α-glucose and β-glucose, with structures:
Biological molecules Page 2
, Polysaccharides are formed by the condensation of many glucose units.
• Glycogen and starch are formed by the condensation of α-glucose.
• Cellulose is formed by the condensation of β-glucose.
The basic structure and functions of glycogen, starch and cellulose.
The relationship of structure to function of these substances in animal cells
and plant cells.
- Glycogen
Glycogen is the main energy storage molecule in animals.
Polysaccharide of alpha glucose joined together by 1, 4 and 1, 6 glycosidic bonds.
It is branched meaning that energy can be released quickly as enzymes can act simultaneously on
these branches.
It is coiled so it is a compact molecule thus maximising the amount of energy it can store
It is insoluble meaning it will not affect the water potential* of cells and cannot diffuse out of cells.
- Starch
Starch stores energy in plants and is a mixture of two polysaccharides:
Hydrolysed to maltose by amylase
Maltose hydrolysed to glucose by maltase
• Amylose :
- an unbranched chain of glucose molecules joined by 1, 4 glycosidic bonds, and as a result amylose is
coiled and thus a very compact molecule storing a lot of energy
- Hydrolyses to amylose, to maltose, to alpha glucose used in respiration
• Amylopectin :
- Amylopectin is branched and is made up of glucose molecules joined by 1, 4 and 1, 6 glycosidic
bonds. Due to the presence of many side branches these can be acted upon simultaneously by many
enzymes and thus broken down to release its energy.
- Cellulose
Cellulose is a component of cells wells in plants and is composed of long, unbranched chains of beta
glucose which are joined by glycosidic bonds.
These long chains of beta glucose form hydrogen bonds between each other forming microfibrils,
strengthening cellulose.
Cellulose is important in stopping the cell wall from bursting under osmotic pressure. This is because
it exerts inward pressure that stops the influx of water. This means that cells stay turgid and rigid,
helping to maximise the surface area of plants for photosynthesis.
*where salt goes, water will follow
Biological molecules Page 3
