AQA A Level biology Unit 1 summary notes

Monomers and Polymers
Monomers

 Monomers are the smaller units from which larger molecules are
made.
 Examples include:
o Monosaccharides (e.g. glucose)
o Amino acids
o Nucleotides

Polymers

 Polymers are large, complex molecules made by joining
monomers together.
 This process is called a condensation reaction:
o It involves the removal of a water molecule as a bond is
formed.
 The reverse process is called a hydrolysis reaction:
o It adds water to break a bond between monomers.




Carbohydrates
Monosaccharides

 Monosaccharides are single sugar molecules and are the basic
units of carbohydrates.
 General formula: (CH₂O)n
 Examples:
o Glucose (C₆H₁₂O₆)
 Exists in two isomers: alpha-glucose and beta-
glucose
 Alpha and beta differ at the carbon-1 (C1) hydroxyl
group

Disaccharides

 Formed when two monosaccharides join via a condensation
reaction.
 A glycosidic bond is formed between them.
 Examples:
o Maltose = glucose + glucose
o Sucrose = glucose + fructose
o Lactose = glucose + galactose
 Disaccharides can be broken down by hydrolysis to release
monosaccharides.

, Polysaccharides

 Polymers made by joining many monosaccharides together.
 Also joined by glycosidic bonds via condensation reactions.

1. Starch (plants)

 Made of alpha-glucose
 Mixture of amylose and amylopectin:
o Amylose: unbranched, coiled chain, compact
o Amylopectin: branched, allows enzymes to access glucose
quickly
 Insoluble, so doesn't affect water potential—ideal for storage

2. Glycogen (animals)

 Also made of alpha-glucose
 Similar to amylopectin but more highly branched
 Compact and rapidly hydrolysed to glucose—ideal for animal energy
storage

3. Cellulose (plants)

 Made of beta-glucose
 Every other beta-glucose is flipped, allowing formation of straight
chains
 Chains form hydrogen bonds, creating microfibrils for structural
strength in plant cell walls

Proteins
Amino Acids

 Proteins are made of amino acids, the monomers of proteins.
 Each amino acid has the same general structure:
o A central carbon (C) atom
o Attached to a hydrogen (H) atom
o An amine group (–NH₂)
o A carboxyl group (–COOH)
o An R group, which is variable and determines the amino
acid’s properties

Dipeptides and Polypeptides

 Dipeptide: two amino acids joined together
 Polypeptide: many amino acids joined in a chain
 Joined by peptide bonds, formed in a condensation reaction
 Peptide bonds can be broken by hydrolysis