All living organisms produce organic molecules called biomolecules. Biomolecules can be broadly divided into biomicromolecules and biomacromolecules. Biomicromolecules such as water, minerals, amino acids, sugars, lipids and nucleotides have molecular weights ranging from eighteen to eight hundred daltons. On the other hand, biomacromolecules such as proteins, lipids, polysaccharides and nucleic acids have molecular weights ranging from ten thousand daltons and above.
The acid-soluble fraction represents the cytoplasmic composition (biomicromolecules) while the acid-insoluble fraction represents the cytoplasm and organelles (biomacromolecules). Together these two fractions represent the complete chemical composition of living organisms. But lipids, with low molecular weight are a part of the biomacromolecules, because they are hydrophobic and get separated along with the acid-insoluble pool.
Polysaccharides are long chains of different monosaccharides. Polysaccharides can be divided into homopolysaccharides or heteropolysaccharides. Polysaccharides, which are formed of one type of monosaccharide units, are homopolysaccharides. Cellulose and starch are made of only glucose units, while inulin is a polymer of fructose. While starch forms helical secondary structures, cellulose does not form any complex helices. Polysaccharides, which are formed of more than one type of monosaccharide units, are heteropolysaccharides. They contain amino sugars and chemically modified sugars as building blocks. Glucosamine and N-acetyl galactosamine are heteropolymers.
Nucleic acids are biomacromolecules in the acid-insoluble fraction of living tissues. A nucleotide acts as a building block of nucleic acid and forms a polynucleotide chain. A nucleotide has a heterocyclic compound, a monosaccharide and a phosphate. The heterocyclic compounds are nitrogenous bases, namely purines and pyrimidines. Purines have six-member and five-member nitrogen-containing rings fused together, while pyramidines have only a six-member nitrogen-containing ring.
The sugar found in nucleotides is either ribose or two-prime deoxyribose. The nucleic acid containing deoxyribose is deoxyribonucleic acid (DNA) while the one with ribose is ribonucleic acid (RNA). Both DNA are RNA carry genetic information in all the cells.