Page 359 - Carrahers_Polymer_Chemistry,_Eighth_Edition

322 Carraher’s Polymer Chemistry

There often occurs a difference in “mindset” between the nucleic acid and protein biopolymers
covered in this chapter and other biopolymers and synthetic polymers covered in other chapters.

Nucleic acids and proteins are structure specific with one conformation. In general, if a molecule dif-

fers in structure or geometry from the specific macromolecule needed it is discarded. Nucleic acids

and proteins are not a statistical average, but rather a specific material with a specific chain length and
conformation. By comparison, synthetic and many other biopolymers are statistical averages of chain
lengths and conformations. All of these distributions are often kinetic/thermodynamic driven.
This difference between the two divisions of biologically important polymers is also refl ected
in the likelihood that there are two molecules with the exact same structure. For molecules such
as polysaccharides and those based on terpene-like structures, the precise structures of individual
molecules vary, but for proteins and nucleic acids the structures are identical from molecule to
molecule. This can be considered a consequence of the general function of the macromolecule. For
polysaccharides, the major, though not the sole function, are energy and structure. For proteins and
nucleic acids, main functions include memory and replication, in additional to proteins also serving
a structural function.
Another difference between proteins and nucleic acids and other biopolymers and synthetic poly-
mers involves the influence of stress–strain activities on the materials properties. Thus, application of

stress on many synthetic polymers and some biopolymers encourages realignment of polymer chains
and regions often resulting in a material with greater order and strength. Counter, application of stress
to certain biopolymers, such as proteins and nucleic acids, causes a decrease in performance (through
denaturation, etc.) and strength. For proteins and nucleic acids, this is a result of the biopolymer already
existing in a compact and “energy favored” form and already existing in the “appropriate” form for the

desired performance. The performance requirements for the two classifications of polymers are different.
For one set, including most synthetic and some biopolymers, performance behavior involves response
to stress–strain application with respect to certain responses such as chemical resistance, absorption
enhancement, and other physical properties. By comparison, the most cited performances for nucleic

acids and proteins involve selected biological responses requiring specific interactions occurring within
a highly structured environment with specific shape and electronic requirements.

10.1 PROTEINS
The many different monodisperse polymers of amino acids, which are essential components of
plants and animals, are called proteins. This word is derived from the Greek porteios, “of chief
importance.” The 20 different α-amino acids are joined together by peptide linkages (Table 10.1).

O R
(10.1)
−(−C−NH− CH−)−

and are also called polyamides or polypeptides. The latter term is often used by biochemists to
denote oligomers or relatively low molecular weight proteins. (Note the structural similarities and
differences between proteins and polyamides-nylons [Section 4.7].)
All α-amino acids found in proteins are of the general structure
NH 2
(10.2)
R−CH−COOH

except glycine
NH 2
(10.3)
H C−COOH
2

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