Download Amino Acids and Their Polymers


Many people are lactose
intolerant. These people
cannot digest milk products
because their bodies do not
produce enough of the
enzyme lactase to digest
lactose, the sugar found in
milk. You will learn what
enzymes are and what
function they serve in the
body.

Amino Acids
◦ What is the general structure of an amino acid?
 An amino acid is any compound that contains an
amino group (—NH2) and a carboxyl group (—COOH) in
the same molecule.
◦ Amino acids have a skeleton that consists of a
carboxyl group and an amino group, both of which
are covalently bonded to a central carbon atom. The
remaining two groups on the central carbon atom
are hydrogen and an R group that constitutes the
amino acid side chain.

Peptides
◦ Which functional groups are always involved in
amide bonds between amino acids?
 A peptide is any combination of amino acids in which
the amino group of one amino acid is united with the
carboxyl group of another amino acid.
 The amide bond between the carboxyl group of one
amino acid and the nitrogen in the amino group of the
next amino acid in the peptide chain is called a peptide
bond.
◦ The amide bonds between amino acids always
involve the central amino and central carboxyl
groups. The side chains are not involved in the
bonding.

Before the invention of electric lighting, wax
candles were a major source of lighting in
homes. In this section, you will read more
about waxes and similar compounds that
make up the class of biomolecules known as
lipids.

Triglycerides
◦ What physical property distinguishes lipids from
other classes of biological molecules?
 Fats, oils, and other water-insoluble compounds are
called lipids.
 Natural fats and oils exist as triesters of glycerol with
fatty acids, which are long-chain carboxylic acids (C12
through C24). This form of lipid is known as a
triglyceride.
◦ Lipids tend to dissolve readily in organic
solvents, such as ether and chloroform, rather
than in highly polar solvents such as water. This
property sets them apart from most biological
substances such as carbohydrates and proteins.
 The hydrolysis of oils or fats by boiling with an
aqueous solution of an alkali-metal hydroxide is called
saponification.
 A typical saponification reaction is shown below.
 Saponification is used to make soap.