TOPIC 2: MOLECULAR BIOLOGY
2.1 Molecules to Metabolism
Molecular Biology: Explains living processes in terms of the chemical substances involved
o This includes explaining the structure and function of chemical substances and
determining their interactions as parts of living processes
Organic Compound: Compound that contains carbon and is found in living things
o Exceptions include: CO2, CN-, CO32-
Carbon is the basis of organic life due to its ability to form stable, complex molecules via
covalent bonding
o Carbon atoms form four bonds allowing a diversity of stable compounds to exist
Other common elements: Nitrogen (3 bonds), Oxygen (2 bonds) & Hydrogen (1
bond)
o Covalent bonds form within molecules, however weaker intermolecular forces can form
between molecules
Life is based on carbon compounds including: carbohydrates,
lipids, proteins & nucleic acids
o These complex macromolecules are often comprised
of smaller recurring sub-units called monomers
Carbohydrates are composed of monomers called
monosaccharaides (single sugar unit)
Cis Trans
o Glucose is the building block of polymers such as
starch, glycogen & cellulose
o Carbohydrates contain C, O and H and can be ring or straight
Ribose
chain structures
Can be differentiated from lipids as they contain
similar numbers of C and O
Also have a 2:1 Hydrogen to Oxygen ratio
Lipids do not contain a reoccurring monomer however several types
contain a fatty acid chain
o Fatty acids are long chains of hydrocarbons with a COOH
group attached at the end. It may contain a double bond
(unsaturated) or only single bonds (saturated)
o Lipids also contain C, O and H but are usually chain structures
They contain very few Oxygen compared to Carbon
Note: Steroids are lipids & have a FOUR RING structure
Proteins are composed of monomers called amino acids, which join to
form polypeptide chains
o Each amino acid contains a carbon connected to an amine
group (NH2) and a carboxylic acid group (COOH)
o A variable group (denoted ‘R’) gives different amino acids
different properties
o Proteins contain the elements C, O, H, N and often S
Nucleic Acids are composed of nucleotide monomers, which join to
form polynucleotide chains
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, o Each nucleotide consists of a pentose sugar, a phosphate group and a
nitrogenous base
The type of sugar and bases differ between DNA and RNA
Metabolism: The web of all the enzyme-catalysed reactions in a cell or organism.
Metabolic reactions are essential as they:
o Provide a source of energy for cellular processes
o Enable synthesis and assimilation for new materials for use within the cell
Anabolism: The synthesis of complex molecules from simpler molecules including the formation
of macromolecules from monomers by condensation reactions
o Condensation Reaction: reaction in which two smaller organic molecules combine to
form a larger molecule accompanied by the formation of water (e.g. esterification)
o Reactions require energy which is usually supplied in the form ATP
Catabolism: The breakdown of complex molecules into simpler molecules including the
hydrolysis of macromolecules into monomers
o Hydrolysis: breaking of chemical bonds by the addition of water molecules
o Reactions release energy
One prevalent scientific theory was that of vitalism, which believed that organic compounds
could only be synthesised by living things as a ‘vital force’ was necessary
o This was falsified by a method of synthesising Urea artificially
Urea (CO(NH2)2) is an organic compound, found in urine and used by the body to excrete
Nitrogen as it is a non-toxic & soluble compound
o According to the theory of vitalism it was predicted that urea could only be made in
living organisms as it was an organic compound, so a vital force was needed
o In 1828, German chemist Wohler synthesised it artificially using Cyanic Acid & Ammonia
o This was the first time an organic compound was synthesised artificially & helped falsify
the theory of vitalism (organic molecules not fundamentally different to inorganic)
However, it was not disproved completely as scientific theories are rarely
abandoned until several pieces of evidence are found
2.2 Water
Water contains 2 Hydrogen & 1 Oxygen which are covalently (shared electrons) bonded together
o However, Oxygen is more electronegative (attracts electrons more strongly) resulting in
the H atoms having a slightly more positive charge and the O atom being negative
This is known as polarity and therefore water
molecules are polar
Intermolecular bonds form between two water molecules, with the
positive pole (H) attracted to the negative pole (O)
o This is known as a Hydrogen Bond (intermolecular force
between O and H atoms)
o When a water molecules evaporates hydrogen bonds are
broken (using heat energy)
Hydrogen bonding and dipolarity explain the cohesive, adhesive,
thermal and solvent properties of water
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2.1 Molecules to Metabolism
Molecular Biology: Explains living processes in terms of the chemical substances involved
o This includes explaining the structure and function of chemical substances and
determining their interactions as parts of living processes
Organic Compound: Compound that contains carbon and is found in living things
o Exceptions include: CO2, CN-, CO32-
Carbon is the basis of organic life due to its ability to form stable, complex molecules via
covalent bonding
o Carbon atoms form four bonds allowing a diversity of stable compounds to exist
Other common elements: Nitrogen (3 bonds), Oxygen (2 bonds) & Hydrogen (1
bond)
o Covalent bonds form within molecules, however weaker intermolecular forces can form
between molecules
Life is based on carbon compounds including: carbohydrates,
lipids, proteins & nucleic acids
o These complex macromolecules are often comprised
of smaller recurring sub-units called monomers
Carbohydrates are composed of monomers called
monosaccharaides (single sugar unit)
Cis Trans
o Glucose is the building block of polymers such as
starch, glycogen & cellulose
o Carbohydrates contain C, O and H and can be ring or straight
Ribose
chain structures
Can be differentiated from lipids as they contain
similar numbers of C and O
Also have a 2:1 Hydrogen to Oxygen ratio
Lipids do not contain a reoccurring monomer however several types
contain a fatty acid chain
o Fatty acids are long chains of hydrocarbons with a COOH
group attached at the end. It may contain a double bond
(unsaturated) or only single bonds (saturated)
o Lipids also contain C, O and H but are usually chain structures
They contain very few Oxygen compared to Carbon
Note: Steroids are lipids & have a FOUR RING structure
Proteins are composed of monomers called amino acids, which join to
form polypeptide chains
o Each amino acid contains a carbon connected to an amine
group (NH2) and a carboxylic acid group (COOH)
o A variable group (denoted ‘R’) gives different amino acids
different properties
o Proteins contain the elements C, O, H, N and often S
Nucleic Acids are composed of nucleotide monomers, which join to
form polynucleotide chains
11
, o Each nucleotide consists of a pentose sugar, a phosphate group and a
nitrogenous base
The type of sugar and bases differ between DNA and RNA
Metabolism: The web of all the enzyme-catalysed reactions in a cell or organism.
Metabolic reactions are essential as they:
o Provide a source of energy for cellular processes
o Enable synthesis and assimilation for new materials for use within the cell
Anabolism: The synthesis of complex molecules from simpler molecules including the formation
of macromolecules from monomers by condensation reactions
o Condensation Reaction: reaction in which two smaller organic molecules combine to
form a larger molecule accompanied by the formation of water (e.g. esterification)
o Reactions require energy which is usually supplied in the form ATP
Catabolism: The breakdown of complex molecules into simpler molecules including the
hydrolysis of macromolecules into monomers
o Hydrolysis: breaking of chemical bonds by the addition of water molecules
o Reactions release energy
One prevalent scientific theory was that of vitalism, which believed that organic compounds
could only be synthesised by living things as a ‘vital force’ was necessary
o This was falsified by a method of synthesising Urea artificially
Urea (CO(NH2)2) is an organic compound, found in urine and used by the body to excrete
Nitrogen as it is a non-toxic & soluble compound
o According to the theory of vitalism it was predicted that urea could only be made in
living organisms as it was an organic compound, so a vital force was needed
o In 1828, German chemist Wohler synthesised it artificially using Cyanic Acid & Ammonia
o This was the first time an organic compound was synthesised artificially & helped falsify
the theory of vitalism (organic molecules not fundamentally different to inorganic)
However, it was not disproved completely as scientific theories are rarely
abandoned until several pieces of evidence are found
2.2 Water
Water contains 2 Hydrogen & 1 Oxygen which are covalently (shared electrons) bonded together
o However, Oxygen is more electronegative (attracts electrons more strongly) resulting in
the H atoms having a slightly more positive charge and the O atom being negative
This is known as polarity and therefore water
molecules are polar
Intermolecular bonds form between two water molecules, with the
positive pole (H) attracted to the negative pole (O)
o This is known as a Hydrogen Bond (intermolecular force
between O and H atoms)
o When a water molecules evaporates hydrogen bonds are
broken (using heat energy)
Hydrogen bonding and dipolarity explain the cohesive, adhesive,
thermal and solvent properties of water
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