AQA A level Biology - topic 1 Biological Molecules
This content is for Year 1/AS Level and is the first
topic you will learn and need to know.
This topic is called Biological Molecules
Biological Molecules
Monomers and Polymers
Monomers
Definition: Small, basic, repeating units that can join together to
form larger molecules.
Examples:
o Monosaccharides → e.g. glucose, galactose
o Amino acids → building blocks of proteins
o Nucleotides → building blocks of DNA/RNA
Definitions are below
Polymers
Definition: Large, complex molecules made up of many monomers
joined together in a repeating pattern.
Examples:
o Carbohydrates → polysaccharides (starch, glycogen, cellulose)
made from monosaccharides
o Proteins → made from amino acids
o DNA/RNA → made from nucleotides
Definitions are below
How Monomers Join to Form Polymers
, Condensation reactions:
o Two monomers join together.
o A molecule of water (H₂O) is released.
o A covalent bond is formed (e.g. glycosidic bond in
carbohydrates, peptide bond in proteins, phosphodiester bond
in nucleic acids).
How Polymers Are Broken Down
Hydrolysis reactions:
o Break the covalent bonds between monomers.
o A molecule of water is used to break the bond.
o Polymers split into smaller molecules (or monomers).
Key Points to Remember (Exam Style)
State that most biological molecules are based on carbon (organic
molecules).
Always mention condensation (water released) and hydrolysis
(water used).
Know at least three examples of monomers and the polymers they
form.
Link to bonds where relevant (glycosidic, peptide, phosphodiester).
Monosaccharides
Definition: Single sugar molecules (the monomers of
carbohydrates).
General formula: (CH_2O)_n where n is usually 3–7.
Examples:
o Glucose – main respiratory substrate
o Galactose – found in lactose
o Fructose – found in fruit
Functions: Provide quick energy (small, soluble, easily transported
and broken down in respiration).
Amino Acids
Definition: Monomers of proteins.
This content is for Year 1/AS Level and is the first
topic you will learn and need to know.
This topic is called Biological Molecules
Biological Molecules
Monomers and Polymers
Monomers
Definition: Small, basic, repeating units that can join together to
form larger molecules.
Examples:
o Monosaccharides → e.g. glucose, galactose
o Amino acids → building blocks of proteins
o Nucleotides → building blocks of DNA/RNA
Definitions are below
Polymers
Definition: Large, complex molecules made up of many monomers
joined together in a repeating pattern.
Examples:
o Carbohydrates → polysaccharides (starch, glycogen, cellulose)
made from monosaccharides
o Proteins → made from amino acids
o DNA/RNA → made from nucleotides
Definitions are below
How Monomers Join to Form Polymers
, Condensation reactions:
o Two monomers join together.
o A molecule of water (H₂O) is released.
o A covalent bond is formed (e.g. glycosidic bond in
carbohydrates, peptide bond in proteins, phosphodiester bond
in nucleic acids).
How Polymers Are Broken Down
Hydrolysis reactions:
o Break the covalent bonds between monomers.
o A molecule of water is used to break the bond.
o Polymers split into smaller molecules (or monomers).
Key Points to Remember (Exam Style)
State that most biological molecules are based on carbon (organic
molecules).
Always mention condensation (water released) and hydrolysis
(water used).
Know at least three examples of monomers and the polymers they
form.
Link to bonds where relevant (glycosidic, peptide, phosphodiester).
Monosaccharides
Definition: Single sugar molecules (the monomers of
carbohydrates).
General formula: (CH_2O)_n where n is usually 3–7.
Examples:
o Glucose – main respiratory substrate
o Galactose – found in lactose
o Fructose – found in fruit
Functions: Provide quick energy (small, soluble, easily transported
and broken down in respiration).
Amino Acids
Definition: Monomers of proteins.
