Biopolymers include natural high-molecular compounds that form the structural basis and provide normal activity of all living organisms.
There are three main types of biopolymers: polysaccharides, nucleic acids, and proteins. Each of them is built from corresponding monomeric units bonded by covalent bonds: polysaccharides - from monosaccharide units, nucleic acids - from mononucleotide units, proteins - from amino acid units.
Chapter 25
CARBOHYDRATES: MONOSACCHARIDES
Monosaccharides are the simplest representatives of carbohydrates. The term "carbohydrates" emerged already in the middle of the 19th century due to the fact that many simple members of this group were described by the empirical formula Сn(H2O)m and formally could be assigned to hydrates of carbon. Later the so-called non-classic carbohydrates were also discovered - they did not correspond to the general formula shown above (deoxyribose С5Н10О4, amino sugars, and several others). ,evertheless, the term "carbohydrates" is also currently used, along with less commonly encountered terms "saccharides" or simply "sugars".
Carbohydrates include substances from low-molecular ones, consisting of only several carbon atoms (a group of monosaccharides), to polymers with a molecular weight of several millions (polysaccharides). An intermediate group includes oligosaccharides (Greek oligos - a few) that consisting of a relatively small number of monomeric units.
25.1. Structure and stereoisomerism
In the earliest period of modern organic chemistry it was already determined that monosaccharides had properties of polyhydroxylic alcohols and aldehydes (or ketones). Based on this, they have been defined (and are still defined) as polyhydroxy carbonyl compounds, for example, ofthe general formula НОСН2[СН(ОН)]nCH=O. However, several chemical properties did not comply with that, which led to the idea of a cyclic structure of monosaccharides.