PROTEINS
Carbon, Hydrogen, Oxygen, Nitrogen and
sometimes Sulphur
Polymers made up of Amino acids
(monomer)
20 commonly occurring amino acids
Structure of an amino acid
• Amino acid
• Dipeptide
• Polypeptide
R Groups
Lysine
Valine
Phenylalanine
Alanine
How is a protein Constructed?
This is a CONDENSATION reaction
Polypeptide chain
Hydrolysis of Protein
Structure of Protein
• Primary
• Secondary
• Tertiary
Primary Structure
•The specific sequence of amino acids joined by peptide bonds
•Long, straight chain of amino acids joined together.
•Determines the function
of the protein
Importance of primary structure
• Determines ultimate shape and function of
protein
• A change in any one amino acid in the
primary sequence, could lead to change in
shape or function of protein
• Therefore, protein’s shape is VERY
SPECIFIC to its function
Secondary Structure
The secondary structure formed by the Hydrogen bonds
formed between amine and carboxyl groups of different amino acids.
http://www.johnkyrk.com/aminoacid.html good for Primary and Secondary struc
Tertiary structure
The specific tertiary structure of a protein is the specific folding of the
secondary structures and is held together by HYDROGEN, IONIC, and
DISULPHIDE bonds.
https://mywebspace.wisc.edu/jonovic/web/proteins.html Good for Tertiary struc
Quaternary Structure
Fibrous and Globular Proteins
• Fibrous-structural roles. E.g Keratin in
nails, Collagen in bone
• Globular-enzymes, antibodies & hormones
E.g. Insulin
Fibrous protein
• Insoluble because Rgroups are non-polar
• Secondary structure
of long polypeptide
chains forming
fibres or sheets.
• Fibres give strength,
sheets flexibility.
Globular Proteins
• Highly folded and
coiled polypeptide
chains (complex
tertiary structure)
• Soluble with a
specific tertiary
structure
Denaturation of proteins
• Alteration of tertiary structure and
loss of 3D shape so protein cannot
function (often irreversible).
• Caused by high temperature, pH and
heavy metals.
Biuret test for Proteins
• Add dilute NaOH and
dilute copper sulphate
to sample.
• blue  purple, lilac or
mauve colour indicates
protein present
• If sample remains blue
no protein is present
Summary
Recap questions.
• 1. What is the monomer of a protein?
• 2. Draw an amino acid and label the amino
group, carboxylic acid group and the R group?
• 3. There are twenty naturally occurring amino
acids, how do they differ from each other?
• 4. Which bond holds together two amino acids
and what is this molecule now called?
• 5. What is the primary structure of a protein and
which bonds are present?
Recap questions.
• 6. What is the secondary structure, which
bonds are present and can you give
examples?
• 7. What is the tertiary structure, which
bonds are present?
Biuret test for Proteins
• Add dilute NaOH and
dilute copper sulphate
to sample.
• blue  purple, lilac or
mauve colour indicates
protein present
• If sample remains blue
no protein is present
EXPERIMENT TITLE:
AIM OF THE EXPERIMENT:
INDEPENDENT VARIABLE:
DEPENDENT VARIABLE:
(Variable changed or set
(Variable you usually find out and record.
by the investigator)
It is DEPENDENT on the INDEPENDENT
variable)
HYPOTHESIS
(What do you predict may happen?)
CONFOUNDING VARIABLES:
Other variables that may affect your experiment. Are there any confounding variables you need to
keep constant?
YOUR CONTROL:
(An experiment to make sure that it IS your Independent variable affecting your dependent variable?
Usually done by ruling out the confounding variables.)
Procedure
1 Place a sample to be tested in a test tube
2 Pour a little dilute alkaline solution (sodium or potassium hydroxide) into the tube.
3 Carefully pour a little dilute copper sulphate solution into the tube. These two chemicals,
sodium/potassium hydroxide and copper sulphate solution constitute Biuret reagent. Gently shake the
tube.
4
Notice that when the two reagents are mixed a darker blue colour results but not purple/mauve.
5 Carry out control tests a) using water instead of protein b) testing with pure protein.
6 Carry out this test on other required samples.
7 Note the colours and record which substances contain protein.
Note
This test does not work for all proteins. It works for soluble ones.