Biochemistry
Proteins
Learning Objectives
By the end of this lesson you will be able to explain that:
The elements which make up proteins are carbon,
hydrogen, oxygen, nitrogen (plus a few others).
Amino acids are the monomers of which proteins are
composed.
The condensation of amino acids leads to the
formation of dipeptides, polypeptides and proteins.
Hydrolysis of proteins reverses this process
The primary, secondary and tertiary structures of
proteins gives them their properties
relationship of structure to function in fibrous and
globular proteins.
A diverse group of biochemicals
structure e.g. collagen (bone, cartilage, tendon), keratin (hair), actin
(muscle)
enzymes e.g. amylase, pepsin, catalase, etc (>10,000 others)
transport e.g. haemoglobin (oxygen), transferrin (iron)
pumps e.g. Na+K+ pump in cell membranes
motors e.g. myosin (muscle), kinesin (cilia)
hormones e.g. insulin, glucagon
receptors e.g. rhodopsin (light receptor in retina)
antibodies e.g. immunoglobulins
storage e.g. albumins in eggs and blood, caesin in milk
blood clotting e.g. thrombin, fibrin
lubrication e.g. glycoproteins in synovial fluid
toxins e.g. diphtheria toxin
antifreeze e.g. glycoproteins in arctic flea
and many more!
Structure
Functional group
Amino group
Carboxyl group
R-group give the amino acid its properties.
Can contain S
dipeptides
The formation of a dipeptide results from the
condensation reaction between two amino
acids.
H2O
Dipeptides
peptide bridge
N-terminus
C-terminus
Polypeptides
Several amino acids linked together!
Polypeptides that fold up and have a 3-D
structure are called proteins
4 structures to be aware of…
Primary Structure
This is just the sequence of the amino acids
in the chain.
Secondary Structure
Alpha Helix
Beta sheets
Tertiary structure
The 3-D structure
Every protein has a unique 3-
D structure
Arises from:
hydrogen bonds, which are
weak.
ionic bonds between R-
groups with positive or
negative charges, which are
quite strong.
sulphur bridges - covalent S-S
bonds between two cysteine
amino acids, which are
strong.
Sulphur bridge
Quaternary Structure
This is only found in
proteins consisting of
more than one
polypeptide chain.
Globular and fibrous proteins
Most proteins are globular
Some are fibrous
Some have regions of both!
Independent study
Compare the structures and functions of
globular and fibrous proteins.
Biochemical tests
Biuret test for protein
grind up sample
add Biuret solution
lilac colour indicates protein
present