Amino acids

After studying this section you should be able to:

  • describe the acid–base properties of amino acids and the formation of zwitterions
  • explain the formation of polypeptides and proteins as condensation polymers of amino acids
  • describe the acid hydrolysis of proteins and peptides

Amino acids

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  • There are 22 naturally occurring amino acids.

Acid–base properties of amino acids

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  • At the isoelectric point, the amino acids exist in equilibrium with its zwitterion form.

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  • Because of their  reactions with strong acids and strong bases,amino acids act as buffers and help to stabilise the pH of living systems.

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Physical properties of amino acids

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Polypeptides and proteins

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Each peptide link forms:

  • between the carboxyl group of glycine and the amino group of alanine
  • with loss of a water molecule in a condensation reaction.

Further condensation reactions between amino acids build up a polypeptide or protein.

  • For each amino acid added to a protein chain one water molecule is lost.
  • Most common proteins contain more than 100 amino acids.
  • Each protein has a unique sequence of amino acids and a complex three-dimensional shape held together by intermolecular bonds including hydrogen bonds.
  • A polypeptide is the name given to a short chain of amino acids linked by peptide bonds. A protein is simply the name given to a longchain polypeptide.

Hydrolysis of proteins

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PROGRESS CHECK

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