Download Protein functions part 2 File

a-keratin is the structural protein of hair, horns and nails
Actin and myosin are
the contractile
proteins of muscle
Tubulin is the protein of the
microtubules; eukaryotic
cilia and mitotic spindles
are composed of
microtubules
Thrombin and
fibrin are blood
clotting proteins
Thrombin is an
enzyme that catalyses
the conversion of the
soluble blood protein
fibrinogen into fibrin
Fibrin forms the
fibres that trap
red blood cells
to form a clot
Antibodies (immunoglobulins) are the proteins of the immune
system; antibodies are manufactured by the B-lymphocytes and
interact with specific, foreign antigens that gain entry to the body
These mussels secrete specialised glue proteins to
attach themselves to the rocks
 Proteins made from monomers called amino acids
 All amino acid possess amino and carboxylic acid ends
 There are 20 different naturally occurring amino acids
 Amino acids differ by in the nature of their R groups
 Amino acids bond together forming peptide bonds
 When two amino acids bond during a condensation
reaction, the resulting molecule is a dipeptide
 When many amino acids bond together, the resulting
molecule is referred to as a polypeptide
 Chains of amino acids numbering greater than 100 are
generally referred to as proteins
 Individual amino acids may be neutral, basic or acidic
 Two amino acids, namely cysteine and methionine,
possess sulphur atoms in their R groups
 The type, number and sequence of amino acids
forming the original linear chain of a protein is termed
the primary structure of a protein
 Different proteins have different primary structures
 The primary structure determines the final shape of
the protein molecule
 The linear chain of amino acids making up the
primary structure of the protein bends and folds in
various ways to form the secondary structure of the
protein
 Two main types of secondary structure are found in
proteins - the beta pleated sheet and the alpha helix
 The alpha helix forms when the linear chain coils into
a right handed helix
 The beta pleated sheet forms when the linear chain
folds back on itself many times
 Hydrogen bonds play a major part in stabilising the
secondary structure of proteins
 Many proteins bend and fold further to form globular
tertiary structures
 Myoglobin is a globular protein displaying the tertiary
level of structure
 Myoglobin is a protein found in muscle cells
 Proteins consisting of more than one polypeptide chain
display quaternary structure
 Haemoglobin is a protein consisting of more than one
polypeptide chain
 Haemoglobin consists of four separate polypeptide
chains held together by weak van der Waals forces
 Each polypeptide chain in haemoglobin contains a
haem group that binds to molecular oxygen
 The role of haemoglobin is to transport oxygen
molecules from the lungs to the body tissues
 A variety of different bonds stabilise the secondary
and tertiary structures of proteins
 Hydrogen bonds form between oxygen and hydrogen
atoms within the main amino acid chain and between
the R groups
 Disulphide bridges form between sulphur atoms in the
R groups of amino acids such as cytseine
 Ionic bonds form between charged amino groups and
charged carboxylic acid groups
 Hydrophobic interactions occur between R groups that
have clustered towards the centre of protein molecules
due to their hydrophobic nature
 The Biuret test is used to detect proteins; a positive
result gives a violet/lilac colour