Compound structures carbohydrates

In carbohydrates the polymer forms have mostly not more than two different monomers in
their structure. Glucose is the only monomer in the most common polysaccharides - starch,
cellulose and glycogen. The difference in functions among polysaccharides results from
the different types of glycosidic bond. Starch and glycogen have -glycosidic linkages, and
they function as a source of energy of plants or animals and humans respectively.
Cellulose, chitin, and peptidoglycans have -glycosidic linkages, and they serve as a
structural element in plants and lower animals.
Proteins are more differentiated polymers. In the human organism they may contain as
many as 20 different amino acids. The three-dimensional conformation of proteins takes
on specific forms that achieve the protein’s ability to function.
Lipids have no monomer or polymer forms as such; they all have the energized form of
acetate as acetyl-CoA at the beginning of their anabolic pathway. They have the
possibility to form secondary structures in the form of membranes or micelles.
Characterization
Carbohydrate, protein, and lipid structures can vary in complexity of form, from storage
forms, such as granules or globules in cells, to functionally important helix or planar forms
in carbohydrates and proteins, fibrous or globular conformations of proteins, or micelle
and membrane lipid structures. In multi-cellular higher organisms, storage forms will occur
in cells that are related to the stored compound, i.e. glycogen in liver and muscle cells,
lipids in fat cells. All complex compounds in an organism are produced within the
organism itself and are also specific to it.
Bonds
Covalent bonding is the predominant type of linkage in the structure of carbohydrates
(including the glycosidic linkage) and the primary structure of proteins (including the
peptide bond). The basic form of lipids is also based on covalent bonding. Covalent bonds
are important in the basic structure of compounds. It is the main type of bonding in starch.
Additional hydrogen bonding is necessary for the final shape of structural polysaccharides
such as cellulose and the structural protein collagen and it allows for the formation of
-helices and -pleated sheets in the secondary structure of proteins. Hydrogen bonds
give additional stability to the structure of compounds. This renders them essential in
structural compounds. More basic forms of life rely on hydrogen bonds in carbohydrates
for their structure. Together with covalent disulfide bonds, electrostatic forces of attraction,
and hydrophobic interactions, hydrogen bonds enable the specific conformations of
proteins that determine the proteins’ functional ability.
Hydrophobic interactions allow for micelle and membrane formation, the typical organic
forms of lipids. Hydrophobic interactions are not based in the first place on the principle
of attraction, as are all other linkages, but on the principle of repulsion. They take place
spontaneously in the watery milieu of the body without the addition of extra energy.
Hydrophobic interactions in lipids allow for the organically essential division of aqueous
fluids in living organisms, into compartments. This makes differentiated functioning of
organisms possible. There is a degree of hydrogen bonding and electrostatic forces of
attraction in lipids, as well as van der Waals bonds.
Characterization
Covalent bonding is prototypical in carbohydrates. Hydrogen bonding allows for more
stable structures both in structural carbohydrates as well as in proteins. Hydrophobic
interactions are not actually bonds; they are based on the principle of sequestering rather
than bonding and occur spontaneously. They play a prominent role in lipid structures and
allow for the most complicated, and yet most basic, structuring principles of living
organisms.
QUESTION: Do different types of linkages represent different
types of energy? (see also Chapter 6.)
Conclusion: Linkages hold potential energy and they determine the structure and function
of compounds in organisms.