Proteins (I)
Elements
• C
• H
• O
and
• N
sometimes
• S
Textbook p98-99
Testing for proteins
• Biuret test (pale blue colour containing sodium
hydroxide and copper sulfate)
The chemicals react
with the peptide
bonds found in
protein, which
results in a colour
change to lilac.
Does not require
any heating
What are proteins
made from?
Acid group
Amino group
Amino acids
• 20 different types
• Each amino acid has an amino group at one
end and an acid group at the other.
R groups
• Can be
–
–
–
–
–
–
–
–
–
Big
Postively charged
Negatively charged
Acidic
Basic
Hydrophobic
Hydrophilic
Include Sulphur
Ring structures
Such properties will
influence the higher level
structures of the protein
– more of this later
Textbook p98-99
Plants
Animals
• Manufacture the
• Must take amino acids in as
amino acids they need
part of their diet.
• Nitrate – used to form • 8-10 of the 20 amino acids
amino groups which
are essential amino acids
are then bonded to
(meat and soya)
organic groups.
• Can’t store excess amino
acids – amino group makes
them toxic
• Deamination
Forming peptide bonds
• Condensation reaction
• Peptide bond formed. This can be broken by a hydrolysis
reaction.
Proteins from amino acids
• Dipeptides
• Polypeptides (10 or more amino acids) and
proteins
Amino acids in proteins are known as residues
(due to loss of the water molecule and therefore
part of the amino acid structure)
Draw four amino acids joined together with peptide
bonds (use general structure with the R group)
Making polypeptides and proteins
• On ribosome (protein synthesis)
• Uses mRNA
• According to the code on the mRNA the amino
acids are assembled in the right order and
then joined by a peptide bond.
Primary structure of proteins
• What is it?
The primary structure of a
protein is given by the specific
sequence of amino acids that
make up the protein
Consider a protein chain that is four amino acids
long....
It has 20 x 20 x 20 x 20 possibilities = 160,000!
What codes for each of the proteins primary structures?
Breaking down proteins
• Enzymes involved... Protease enzymes
Looking at two examples:
1. Hormone regulation
2. Ageing
Answers to Q8 from booklet