Major families of biopolymers are
polysaccharides (carbohydrates),
peptides, and
polynucleotides. Many variants of each are known.
Proteins and peptides and
fructose form
sucrose. The synthesis of glycogen in the body is driven by the enzyme
glycogen synthase which uses a
uridine diphosphate (UDP) leaving group.Proteins are characterized by
amide linkages (-N(H)-C(O)-) formed by the condensation of
amino acids. The sequence of the amino acids in the polypeptide backbone is known as the
primary structure of the protein. Like almost all polymers, protein fold and twist, forming into the
secondary structure, which is rigidified by
hydrogen bonding between the
carbonyl oxygens and amide hydrogens in the backbone, i.e. C=O---HN. Further interactions between residues of the individual amino acids form the protein's
tertiary structure. For this reason, the primary structure of the amino acids in the polypeptide backbone is the map of the final structure of a protein, and it therefore indicates its biological function.
Carbohydrates and
guanine forming a
phosphodiester bond, the
triphosphorylated ribose of the incoming nucleotide is attacked by the 3'
hydroxyl of the polymer, releasing
pyrophosphate. Carbohydrates arise by condensation of
monosaccharides such as
glucose. The polymers can be classified into
oligosaccharides (up to 10 residues) and
polysaccharides (up to about 50,000 residues). The backbone chain is characterized by an ether bond between individual monosaccharides. This bond is called the
glycosidic linkage. These backbone chains can be unbranched (containing one linear chain) or branched (containing multiple chains). The glycosidic linkages are designated as
alpha or beta depending on the relative
stereochemistry of the
anomeric (or most
oxidized) carbon. In a
Fischer Projection, if the glycosidic linkage is on the same side or face as carbon 6 of a common biological saccharide, the carbohydrate is designated as
beta and if the linkage is on the opposite side it is designated as
alpha. In a traditional "
chair structure" projection, if the linkage is on the same plane (equatorial or axial) as carbon 6 it is designated as
beta and on the opposite plane it is designated as
alpha. This is exemplified in
sucrose (table sugar) which contains a linkage that is
alpha to glucose and
beta to
fructose. Generally, carbohydrates which our bodies break down are
alpha-linked
(example: glycogen) and those which have structural function are
beta-linked (example:
cellulose).
Nucleic acids Deoxyribonucleic acid (DNA) and
ribonucleic acid (RNA) are the main examples of
polynucleotides. They arise by condensation of nucleotides. Their backbones form by the condensation of a hydroxy group on a
ribose with the
phosphate group on another ribose. This linkage is called a
phosphodiester bond. The condensation is catalyzed by
enzymes called
polymerases. DNA and RNA can be millions of nucleotides long thus allowing for the
genetic diversity of life. The bases project from the pentose-phosphate polymer backbone and are
hydrogen bonded in pairs to their
complementary partners (A with T and G with C). This creates a
double helix with pentose phosphate backbones on either side, thus forming a
secondary structure. ==References==