Page 412 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Naturally Occurring Polymers—Animals 375

10.15 SUMMARY

1. Physically there are little difference in the behavior, study, or testing of natural and synthetic
polymers. The fundamental principles that underpin the behavior of macromolecules apply
equally to both synthetic and natural polymers. Both groupings contain members that exhibit
characteristics that are unique to that grouping. Even so, differences within even these group-
ings are by degree rather than kind with the fundamental laws continuing to be applicable.
2. Contributions from studying both natural and synthetic polymers are being used to forward the
science of both sets of macromolecules.
3. Organic polymers are responsible for the very life—both plant and animal—that exists. Their
complexity allows for the variety that is necessary for life to occur, to reproduce, and to adapt.
Structures of largely linear natural and synthetic polymers can be divided into primary struc-
tures used to describe the particular sequence of (approximate) repeat units, secondary struc-
ture used to describe the molecular shape or conformation of the polymer, tertiary structure
that describes the shaping or folding of macromolecules, and quaternary structure that gives
the overall shape of groups of tertiary-structured macromolecules. The two basic secondary
structures are those of the helix and sheets.
4. Proteins are composed of 20 different alpha-amino acids and contain peptide linkages similar
to those present in polyamides. With the exception of glycine, all the amino acids contain a chi-
ral carbon. The geometrical shape and behavior of the giant proteins is a product of the various
preferred geometries that allow the molecules to balance factors such as preferred bond angle,
secondary bonding forces, emphasizing hydrogen bonding, size, shape, hydrophobic/hydro-
philic interactions, external/internal chemical environments, and cross-linking. Small chains
of amino acids are referred to as peptides.

5. Secondary structures for proteins are generally fibrous and globular. Proteins such as keratines,
collagen, and elastin are largely fibrous and have secondary structures of sheets and helixes.

Many of the globular proteins are composed of protein chains present in secondary structures
approximating helixes and sheets.
6. Enzymes are one important group of proteins. They serve as natural catalysts immobilizing
various components that will be later joined or degraded.
7. The two major types of nucleic acids are DNA and RNA. Nucleic acids are polyphosphate
esters containing the phosphate, sugar, and base moieties. Nucleic acids contain one of fi ve
purine/pyrimidine bases that are coupled within double-stranded helixes. DNA, which is an
essential part of the chromosome of the cell, contains the information for the synthesis of
protein molecules. For double-stranded nucleic acids, as the two strands separate, they act as
a template for the construction of a complementary chain. The reproduction or duplication of
the DNA chains is called replication. The DNA undergoes semiconservative replication where
each of the two new strands contains one of the original strands.
8. The flow of biological genome knowledge is from DNA to RNA via transcription and from

RNA to direct protein synthesis via translation.
9. Genetic engineering is based on chemical manipulations that are exactly analogous to those
carried out by chemist in basic chemistry laboratories, but it involves the use of biological
agents.
10. Much that is occurring with genes, proteins, mutations, chain folding, and other important
molecular biology-related efforts is polymer chemistry applied to natural systems and we have
much to offer to assist in these ventures.

GLOSSARY

α-helix: Right-handed helical conformation.
β arrangement: Pleated sheet-like conformation.

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