Page 5 - Lesson Notes - Biomolecules 1

iv. Aromatic Amino Acids
These contain aromatic rings in their side chain, e.g., Phenylalanine, tyrosine and
tryptophan.
Zwitter Ion
Zwitter ion formation is anoth’er particular property of amino acid. It is a neutral
molecule (with positive and negative charge), having the ionizable nature of —
NH 2 and —COOH groups. Hence, in splutions of different pHs, the structure of amino
acid changes variably.

3. Lipids
Lipids are the esters of fatty acids and alcohol. These are generally insoluble in
water. They could be simply fatty acids.
Fatty acids are the organic acids having hydrocarbon chains that end in a carboxylic
group (—COOH). The carboxylic group is attached to an R group that could be a
methyl (—CH 3) or ethyl (—C 2H 5) or higher number of —CH 2 groups (1 carbon to 19
carbons), e.g., Palmitic acid has 16 carbons including carboxyl carbon.
Arachidonic acid has 20 carbon atoms including the carboxyl carbon.
Depending upon the types of bonds present, fatty acids are of following two types
i.Saturated Fatty Acids
Fatty acids which do not have double bonds, (C—C). These are generally solid at
room temperature.
ii. Unsaturated Fatty Acids
Fatty acids which contain one or more than one double bonds (C = C). These are
generally liquid at room temperature.

Difference between saturated and unsaturated fatty acids