AS/A LEVEL NOTES SECTION 1

1.1 Introduction to biological molecules
Moles

 A mole is the SI unit for measuring the amount of a substance (mol) – the molecular mass
(molecular weight) expressed in 1 gram
 Molar solution = contains 1 mole of solute in each litre of solution.

Example – Na= 23 + Cl= 35.5 is NaCl= 58.5 so 1M solution of NaCl contains 58.5 grams of NaCl in 1
litre of solution

Bonding and formation of molecules

Covalent bonding –

 atoms share pairs of electrons (from outershell) filling their outershell = more stable
compound, molecule formed, occurs between two non-metals

Ionic bonding –

 ions of opposite charges attract one another, they form an electrostatic attraction = ionic
bond, occurs between a metal and a non-metal

Hydrogen bonding –

 the electrons within a molecule are not evenly distributed, 1 region is more negatively
charged than the rest of the molecule, negative region of 1 polarised molecule and the
positively charged region attract each other = weak electrostatic bond
 Polarised – a molecule with uneven distribution of charge (polar molecule)

Polymerisation and macromolecules

 Monomers can be linked together to form long chains called polymers through the process
of polymerisation
 Made of carbon, oxygen and hydrogen – biological molecules
 Polymers like polythene and polyester are industrially produced
 However others like polysaccharides, polypeptides and polynucleotides are naturally made
by living organisms

Condensation and hydrolysis reactions

 Condensation reaction – formation of polymers, 2 molecules combine to form a more
complex one, water is formed as a condensation
 Hydrolysis reaction – polymers are broken down with the addition of water breaks the
bonds that link the monomers in the polymer




 Metabolism – all the chemical processes that take place in living organisms

, 1.2 Carbohydrates – monosaccharides
Carbohydrates are made up of carbon, hydrogen and oxygen, they can be small while others are
large.

Number of carbon atoms Type of monosaccharide
in monosaccharide
3 triose

4 tetrose

5 pentose

6 hexose

7 heptose



Monosaccharides

 A single monomer is called a monosaccharide, a pair of monosaccharides can be combines
to form a disaccharide or many combined make a
polysaccharide.
 Carbon can readily link to one another to form a
chain
 Sweet tasting + Soluble
 (CH2O)n, N is any number between 3 and 7
 Crystalline
 Examples – glucose, fructose and galactose
 glucose has 2 isomers: alpha α-glucose and beta β-
glucose
 Position of hydrogen and hydroxyl groups on carbon atom 1 inverted.
 isomers = 2 or more compunds with the same formula but different arrangement of atoms

Testing reducing sugars

 All monosaccharides and some disaccharides
(maltose) are reducing sugars
 Reduction is gain of electrons, reducing sugar
can donate electron (reduce) another
chemical = benedict reagent
 Benedicts test = blue alkaline copper II sulfate
solution reduces to form insoluble red
paticipate copper I oxide
1. Add 2cm3 of food sample to test tube
2. Add equal volume of benedicts reagent
3. Heat mixture in water bath for 5 minutes
 Differences in colour = semi quantative, can
be used to estimate the approximate amount
of reducing suagr in a sample