Biology Induction
Course Content
AS Biology
A-Level
Biology
AS Practical Work
Career options
Degree options
Research Based IS Task
 Due date: 1st lesson back after the summer holidays
1.
2.
Compare and contrast the structure and function of
prokaryotic and eukaryotic cells. This should be no longer
than 750 words
Reducing sugars are a type of carbohydrate molecule.
Produce an ISA style apparatus list, method and risk
assessment to describe how you would safely test for the
presence of reducing sugars in an unknown solution –
Solution A
Both tasks require you to carry out independent research and your
sources of information must be listed at the end of each task.
Lesson Objectives
 Know the biochemical structure of protein molecules
 Work independently to carry out Biuret tests to investigate if
foods contain protein
 Be confident at safely carrying out investigations in the science
laboratory in preparation for the Unit 3 ISA/PSA skills tests
Biological Molecules - Proteins
 Biological molecules are made up of subunits called MONOMERS
 Monomers join together in chains to form POLYMERS
Proteins
 Made up of: CHONS





Carbon
Hydrogen
Oxygen
Nitrogen
Sulphur (sometimes)
 The monomers in proteins are called AMINO ACIDS
 There are 20 different commonly occurring amino acids
Proteins - Amino Acids
Amino acids are made up of 3
groups
1. Amino group

(-NH2)
2.
Carboxyl group (carboxylic
acid group)
(-COOH)
3.
R group (side chain)
(Varies with the amino acid)
H
H2N-C-COOH
R
 There are 20 different amino
acids and so there are 20
different R groups
Condensation reactions
 Condensation reactions create peptide bonds which hold the individual
amino acid monomers together
 This creates a peptide
Water
Amino acid
monomer R
Amino acid
monomer R’
Condensation reaction – creating a
peptide
R’
R
R
R’
Di-peptide
 More peptides can join to form a polypeptide
 Proteins are made up of one, 2 or more polypeptides
Hydrolysis - Breakdown of Proteins
Hydrolysis – addition of water
R
OH-
R’
H+
H2O
This reaction occurs by
boiling in dilute HCl or
by protease enzymes
R
R’
Protein Structure

1.
2.
3.
4.
Proteins are made up of 4
different structures
Primary -1o
Secondary -2o
Tertiary -3o
Quarternary –4o
YouTube - Protein Structure
Primary structure
 Order of amino acid monomers
in the peptide chain
 The sequence of amino acids
determines the 3-D shape
 A simple protein may be made
up of one polypeptide chain
Secondary Structure
 When the amino acids join together as
a peptide they form shapes or patterns
 Weak Hydrogen bonds form between
polar molecules
 Peptide bonds contain polar H atoms
and Polar O atoms
 Polar H atoms on the amino group have
a small +ve charge
 Polar O atoms of the carboxyl group
have a small -ve charge
Secondary Structure
 The charges allow H bonds to
form between peptide bonds in
different parts of the chain
Secondary Structure
 2 shapes formed
 Alpha helix
 Beta-pleated sheet
 The secondary shape depends
on the primary structure, i.e.
the order of the amino acids
Tertiary Structure
 3-D shape
 Determines the function of the
protein
 Very important in creating the active
site in enzymes
 Shape is held together by
 Hydrogen bonds – numerous but easily
broken
 Ionic Bonds – formed by any carboxyl
and amino group not involved in forming
peptide bonds
 Easily broken by pH changes
 Disulphide bonds – fairly strong
 Hydrogen bonds are weak and easily disrupted
 Ionic bonds formed between carboxyl group and amino
group – NOT peptide formation
 Easily broken with pH changes
 Disulphide bonds are covalent bonds between sulphur atoms
in R groups
 Fairly stong, not easily broken
Tertiary Structure
 3 types of bonds lead to 2 main
kinds of protein
 Fibrous
 Globular
Globular Proteins
 Approximately spherical in
shape
 Usually water soluble
 Tend to have a biochemical
function rather than structural
 E.g. Enzymes or haemoglobin
Fibrous Proteins
 Polypeptides join together to





form long fibres or sheets
Very strong
Insoluble in water
Tend to have structural
functions
E.g. fingernails and hair –
Keratin
E.g. Skin, Bone, Blood vessels
and teeth - collagen
Fibrous Proteins
 1o structure is an unbranched
polypeptide chain
 2o structure is very tightly
wound
 3o structure is a chain twisted
into a second helix
 4o structure 3 of the 3o
structure chains wound together
like fibres in a rope
Quarternary Structure
 A number of polypeptide chains
 Associated non-protein
components called prosthetic
groups
 Together producing the
quarternary structure
Testing for protein molecules in
unknown solutions
You will be investigating 5 unknown solutions and carrying out
a simple practical investigation to determine whether they
contain protein, dipeptides or none
Testing for Protein Molecules
Biuret test
 Biuret 1 = Sodium Hydroxide solution
 Biuret 2 = Copper (II) Sulphate solution
Blue
No proteins or peptides
Violet/Lilac
Proteins
Pink
Peptides
 Copper atoms in the copper (II) sulphate solution form a complex with the N atoms
in the amino group of the peptide bond – this causes a colour change
Method
1.
2.
Add equal volume of Sodium Hydroxide solution to the solution
being tested
Add a few drops of copper (II) Sulphate solution
Evaluate this method!
• Could you carry out
this investigation
with the information
that you have been
supplied with in this
method?
Sodium Hydroxide solution creates alkaline conditions
Testing for protein molecules in
unknown solutions
Health and Safety
 http://www.sciencelab.com/msds.php?msdsId=9925783
 http://www.genesisenergy.com/assets/_RefineryServices/
MSDS/MSDS_Caustic_50_TDC_2010.pdf