1 BIOLOGICAL MOLECULES
Bonding and the Formation of molecules
❖ Covalent bonding - Atoms share a pair of electrons in their outer shells. As a
result the outer shell of both atoms is filled and a more stable compound, a
molecule, is formed.
❖ Ionic bonding - Ions with opposite charges attract one another. This
electrostatic attraction is known as an ionic bond. For example, the positively
charged sodium ion Na+ and negatively charged chloride ion Cl- form an ionic
bond to make sodium chloride. Ionic bonds are weaker than covalent bonds.
❖ Hydrogen bonding - the electrons within a molecule are not evenly
distributed but tend to spend more time at one position. This region is more
negatively charged than the rest of the molecule. A molecule with an uneven
distribution of charge is said to be a polar molecule. A weak electrostatic bond
is formed between the two. Although each bond is individually weak, they can
collectively form important forces that alter the physical properties of
molecules.
Polymerisation and the formation of macromolecules
➢ Certain molecules, known as monomers can be linked together to form long
chains. These long chains of monomers are called polymers and are formed
by the process of polymerisation.
Condensation and hydrolysis reactions
➢ In the formation of polymers by polymerisation in organisms, each time a new
sub-unit is attached a molecule of water is formed. Reactions that produce
water in this way are ‘Condensation Reactions’, the formation of polypeptides
is done through this process.
➢ Polymers can be broken down through the addition of water. Water molecules
are used when breaking down the bonds that link the sub-units of a polymer,
therefore splitting the molecule into constituent parts. This is done through
‘Hydrolysis Reactions’.
Metabolism - all chemical processes that occur in a living organisms
,Water
➢ Described as a polar/ dipolar molecule
➢ The oxygen within the water has more electrons, making the molecule slightly
negatively charged.
➢ The hydrogen within the water has less electrons, making the molecule
slightly positively charged.
➢ Therefore, the molecule is slightly negatively charged and slightly positively
charged.
➢ Water has cohesion properties, creating surface tension - allows small
animals and insects to ‘float’ on the water.
➢ Due to the charges of water, water travels as a column of many water
molecules held together by hydrogen bonds through cohesion.
Properties of water
➢ High heat energy is needed to convert water into water vapour (large amount
of latent heat of vaporisation).
➢ This is important as it aids cooling as only a small amount of water is needed
for a large cooling effect.
➢ High heat energy is needed to raise the temperature (high specific heat
capacity).
➢ Large amounts of energy needs to be lost from water before it freezes (large
latent heat of fusion).
➢ This is important as it provides a constant, stable environment for oceans and
cells.
➢ As water freezes, it expands, this means that frozen water is less dense than
a liquid so floats. The frozen layer of ice acts as an insulator for the water
below so therefore doesn’t freeze.
➢ Water can split larger molecules into smaller molecules by a process called
hydrolysis.
Molecules
Carbohydrates
, 1. Monosaccharides
2. Disaccharides
3. Polysaccharides
Isomers – when a molecule has the same chemical formula but a different structural
formula
Monosaccharides
➢ Sweet tasting and soluble.
➢ Glucose
➢ Galactose
➢ Fructose
Reducing sugars
➢ All monosaccharides
➢ Many disaccharides are reducing sugars.
Benedict’s test
➢ Determines the reducing properties of different sugars.
➢ Benedict’s solution is a turquoise (blue) liquid, containing copper ions (Cu2+)
and sodium hydroxide.
➢ If sugar is reducing, then the copper ions are reduced to Cu+ which in the
presence of alkali sodium hydroxide from copper oxide.
Glucose – reducing
sugar
Sucrose – non-
reducing sugar
Reducing sugars test
1. Mix test solution with an equal
volume of Benedict’s solution.
Hydrochloric acid - breaks
bonds
Sodium hydroxide -
Bonding and the Formation of molecules
❖ Covalent bonding - Atoms share a pair of electrons in their outer shells. As a
result the outer shell of both atoms is filled and a more stable compound, a
molecule, is formed.
❖ Ionic bonding - Ions with opposite charges attract one another. This
electrostatic attraction is known as an ionic bond. For example, the positively
charged sodium ion Na+ and negatively charged chloride ion Cl- form an ionic
bond to make sodium chloride. Ionic bonds are weaker than covalent bonds.
❖ Hydrogen bonding - the electrons within a molecule are not evenly
distributed but tend to spend more time at one position. This region is more
negatively charged than the rest of the molecule. A molecule with an uneven
distribution of charge is said to be a polar molecule. A weak electrostatic bond
is formed between the two. Although each bond is individually weak, they can
collectively form important forces that alter the physical properties of
molecules.
Polymerisation and the formation of macromolecules
➢ Certain molecules, known as monomers can be linked together to form long
chains. These long chains of monomers are called polymers and are formed
by the process of polymerisation.
Condensation and hydrolysis reactions
➢ In the formation of polymers by polymerisation in organisms, each time a new
sub-unit is attached a molecule of water is formed. Reactions that produce
water in this way are ‘Condensation Reactions’, the formation of polypeptides
is done through this process.
➢ Polymers can be broken down through the addition of water. Water molecules
are used when breaking down the bonds that link the sub-units of a polymer,
therefore splitting the molecule into constituent parts. This is done through
‘Hydrolysis Reactions’.
Metabolism - all chemical processes that occur in a living organisms
,Water
➢ Described as a polar/ dipolar molecule
➢ The oxygen within the water has more electrons, making the molecule slightly
negatively charged.
➢ The hydrogen within the water has less electrons, making the molecule
slightly positively charged.
➢ Therefore, the molecule is slightly negatively charged and slightly positively
charged.
➢ Water has cohesion properties, creating surface tension - allows small
animals and insects to ‘float’ on the water.
➢ Due to the charges of water, water travels as a column of many water
molecules held together by hydrogen bonds through cohesion.
Properties of water
➢ High heat energy is needed to convert water into water vapour (large amount
of latent heat of vaporisation).
➢ This is important as it aids cooling as only a small amount of water is needed
for a large cooling effect.
➢ High heat energy is needed to raise the temperature (high specific heat
capacity).
➢ Large amounts of energy needs to be lost from water before it freezes (large
latent heat of fusion).
➢ This is important as it provides a constant, stable environment for oceans and
cells.
➢ As water freezes, it expands, this means that frozen water is less dense than
a liquid so floats. The frozen layer of ice acts as an insulator for the water
below so therefore doesn’t freeze.
➢ Water can split larger molecules into smaller molecules by a process called
hydrolysis.
Molecules
Carbohydrates
, 1. Monosaccharides
2. Disaccharides
3. Polysaccharides
Isomers – when a molecule has the same chemical formula but a different structural
formula
Monosaccharides
➢ Sweet tasting and soluble.
➢ Glucose
➢ Galactose
➢ Fructose
Reducing sugars
➢ All monosaccharides
➢ Many disaccharides are reducing sugars.
Benedict’s test
➢ Determines the reducing properties of different sugars.
➢ Benedict’s solution is a turquoise (blue) liquid, containing copper ions (Cu2+)
and sodium hydroxide.
➢ If sugar is reducing, then the copper ions are reduced to Cu+ which in the
presence of alkali sodium hydroxide from copper oxide.
Glucose – reducing
sugar
Sucrose – non-
reducing sugar
Reducing sugars test
1. Mix test solution with an equal
volume of Benedict’s solution.
Hydrochloric acid - breaks
bonds
Sodium hydroxide -
