Amino acids: amino acids have an amino group consisting of nitrogen and hydrogens at one end of the molecule and an organic acid or carboxyl group at the other end. In addition from the first carbon of the amino acid can attach any one of a number of different functional groups. These give each type of amino acid distinct chemical and physical properties. The amino acids shown in the three dimensional models were slected to illustrate the major kinds of amino acids.
Amino acids are important for several reasons. First they are the monomers or building blocks from which proteins are made. Second many amino acids are the precursors for important neurotransmitters and other signaling molecules in the body such as the hormone melatonin.
In the ball and stick models illustrated below, carbon = gray, hydrogen
= white, oxygen = red, nitrogen=blue and sulfur = yellow.
Glycine: Glycine is the simplest amino acid. On the right side is a carboxyl or organic acid group consisting of a carbon double(gray) bonded to an oxygen(red) and single bonded to a hydroxyl group(OH). On left side is a nitrogen(blue) bonded to three hydrogens and the second carbon. This amino group is basic. Thus the name amino acid. Also these substances can behave either as an acid or base.
is a somewhat more complex amino acid. Notice the small side chain consisting
of three carbons bonded to hydrogens. Each amino acid differs in what functional
group it has hanging from the second carbon.
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Tryptophan is the starting material for serotonin, an important neurotransmitter
and for melatonin, a hormone produced by the pineal gland. Note the large
two rings, one of which contains nitrogen.
Phenylalanine. Phenylalanine is a good example of an amino acid with a non polar (hydrophobic) side group. The large ring is a benzene ring.
is an example of an amino acid with a functional group that ionizes in
solution.This is aspartate is it might
be in solution. The carboxyl group has lost a hydrogen. Also if you note
the two oxygens coming from the bottom of the molecule, one was originally
a hydroxyl group and has now lost its hydrogen to the solution. Thus the
functional group is a negatively charged ion.
This will be very hydrophilic.
is an example of amino acid containing sulfur. These are important structural
amino acids because two sulfurs from distant amino acids in a polypeptide
can link together to form covalent bonds that help to stabilize the structure
of the polypeptide. This is cysteine. The yellow globe at the bottom of
the picture represents a sulfur atom.
pgd. revised 06/15/02