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Proteins are long chains of amino
acids.
Each amino acid is composed of an
organic molecule with a carboxyl end and an amino
end
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- Proteins form when amino acids are
joined together by dehydration synthesis, i.e.
the hydrogen from the amino end of one molecule
combines with the hydroxyl group of the
carboxylic acid end of another amino acid
molecule..
- This bond is called a peptide
bond and the compound formed is called a
peptide.
- The lengths of polypeptide chains
vary widely fromas short as 9 amino acid to
thousands of amino acids.
- Polypeptides with more than 100
amino acid residues are called proteins.
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- The structure of the protein can
be described at four levels.
- Primary Structure is
the sequence of amino acids.
- Secondary Structure arises
through the formation of hydrogen bonds forming a
helix.
- Tertiary Structure
Apart from the simple twisting, most of the
polypeptide chains twist on themselves (mostly
through further hydrogen bonding) to form
tertiary structures.
- Some functional proteins are
infact composed of two or more separate chains
(e.g. insulin and hemoglobin). This is the quaternary
structure of the protein.
- On denaturing (either by heat or
chemicals), proteins retain their primary
structure but lose their secondary, tertiary and
quaternary structures. This would usually cause
them to alter their physical properties including
function.
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