1.2.1 Amino Acids by lanyuehua


									OCR Chemistry A2 (Unit 4)                                                    Amino Acids 1

1.2.1 Amino Acids

Amino acids are the building blocks of proteins – a vital component of all living
They contain a carboxylic acid group and a primary amine group in the same molecule
and so they are said to be bifunctional.

General formula of an α-amino acid:


There are 20 naturally occurring amino acids, which differ only in the nature of the R
group. They are usually called by their common or trivial names.

Physical Properties

They have high melting and boiling points and are usually water-soluble. They have
low solubility in non-polar solvents.
OCR Chemistry A2 (Unit 4)                                                   Amino Acids 2

Zwitterions and the isoelectric point

The acidic carboxyl group and the basic amine group in an amino acid can interact with
each other to form an internal salt, known as a __________________.

Zwitterion (particle containing a negatively charged and positively charged group):

A zwitterion has no overall charge as the positive and negative charges cancel each
other out.

The _____________________ is the pH at which there is no net electrical charge. The
zwitterions of an amino acid exists at this pH value (often around pH6)

Acid and base properties

Every amino acid has a carboxyl group and an amino group. So, depending on the pH
of the solution in which the compound is dissolved, each group can exist in an ionic or
non-ionic form.

In a strongly acidic solution, the amino group is _______________ and the carboxyl
group is ____________________

In a neutral solution the amino group is _______________ and the carboxyl group is

In a strongly basic solution, the amino group is _______________ and the carboxyl
group is ____________________

Key Definitions

Peptide -

Zwitterion -

Isoelectric point -

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