Amino Acids and Proteins describes the amino acid structure and preparations, as well as
the isoelectric pH and electrophoresis. Formation of proteins, protein
structure, sequencing proteins, detection and denaturation of proteins
are also addressed.
The fundamental structure of amino acids is presented and the ways
in which those structures differ is stressed. The general R group
is noted as being acid, base, cyclic, aromatic, indole, etc. The
ten essential amino acids are noted and the importance of ingesting
these compounds discussed. The dependence of one amino acid on another
within human physiology is stressed using the synthesis of tyrosine
from phenylalanine and subsequent results encountered when the body
is unable to perform this synthesis.
Properties of amino acids studied include the formation of dipolar
ions called zwitterions. These structures are used to describe the
reaction of amino acids with acids and bases and the manner in which
these zwitterions may behave as a physiological buffer. Also included
in the study of properties is the important pH designation of the
isoelectric point. The relationship between structure and isoelectric
point is noted. From that discussion, the way in which electrophoresis
works is explained.
The formation of polypeptides and proteins is addressed via the formation
of a peptide link. The importance of blocking the N-terminus or
C-terminus is explained. In the reverse of this process, the identification
of a polypeptide by sequencing is discussed. The series of steps
begins with elimination of disulfide linkages, followed by identification
of the N-terminus using the Edman degradation with phenyl isothiiocyanate
or the Sanger method with 2,4-dinitrofluorobenzene or some similar
method. Complete hydrolysis of a sample to indicate the amino acid
population followed, and the process concludes with partial hydrolysis
of a sample with subsequent analysis. The student is given several
opportunities to determine the sequence of a particular polypeptide.
Proteins are identified and defined. The four ways to describe the
structure of proteins are described with examples of each. It is
noted that while the first three are expected, the fourth only occurs
in limited circumstances.
The detection of proteins always fascinates students because of
their interest in forensics. The two important tests for proteins,
the Xanthproteic test using nitric acid is one the student knows
from experience, although perhaps not by name. There are very few
students who reach this level of chemistry without experiencing
the yellow coloration that arises from a nitric acid spill on the
fingers. The second test, Ninhydrin, involves formation of Ruhemannís
purple, a classic way in which fingerprints may be detected and
The fragile structure of proteins is nowhere better demonstrated
than through discussion of the denaturation process. Students are
often surprised by the methods by which the biological activity
of proteins may be destroyed.