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All the carbon compounds that we get from living tissues can be called biomolecules.

All the carbon compounds that we get from living tissues can be called biomolecules.

Acid-soluble pool: Scientists have found thousands of organic compounds in the acid-soluble pool. The compounds of the acid-soluble pool have molecular weights ranging from 18 to around 800 Daltons (Da) approximately.

Acid insoluble pool: The acid insoluble fraction, has only four types of organic compounds i.e., proteins, nucleic acids, polysaccharides, and lipids. These classes of compounds apart from lipids, have molecular weights in the range of ten thousand Daltons and above.


  • Amino acids are organic compounds containing an amino group and an acidic group as substituents on the same carbon i.e., the α-carbon. Hence, they are called α-amino acids.

  • They are substituted methanes.

  • There are four substituent groups occupying the four valency positions. These are hydrogen, carboxyl group, amino group, and a variable group designated as R group.

  • Based on the nature of the R group there are many amino acids.

  • However, those which occur in proteins are only of twenty types. The R group in these proteinaceous amino acids could be hydrogen (the amino acid is called glycine), a methyl group (alanine), hydroxy methyl (serine), etc.

  • Based on the number of amino and carboxyl groups, there are acidic (e.g., glutamic acid), basic

  • A particular property of amino acids is the ionizable nature of –NH2 and –COOH groups.

  • Hence in solutions of different pHs, the structure of amino acids changes.


  • Lipids are generally water-insoluble. They could be simple fatty acids.

  • A fatty acid has a carboxyl group attached to an R group. The R group could be a methyl (– CH3), ethyl (–C2H5), or a higher number of –CH2 groups (1 carbon to 19 carbons). For example, palmitic acid (16 carbons) and arachidonic acid (20 carbon atoms) including the carboxyl carbon.

  • Fatty acids could be saturated (without double bonds) or unsaturated (with one or more C=C double bonds).

  • Glycerol is a simple lipid which is trihydroxy propane.

  • Many lipids have both glycerol and fatty acids. Here the fatty acids are found esterified with glycerol. They can be then monoglycerides, diglycerides and triglycerides. These are also called fats and oils based on melting point.

  • Oils have lower melting points (e.g., gingerly oil) and hence remain as oil in winter.

  • Phospholipids are found in cell membranes. Lecithin is one example.


  • Nitrogenous bases are heterocyclic rings having a number of carbon compounds.

  • Nitrogen bases areadenine, guanine, cytosine, uracil, and thymine.

  • Nucleosides - Nitrogenous base + sugar. Ex: Adenosine, guanosine, thymidine, uridine, and cytidine.

  • Nucleotides - Nitrogenous base + sugar + Phosphate group. Ex: Adenylic acid, thymidylic acid, guanylic acid, uridylic acid, and cytidylic acid are nucleotides.

  • Nucleic acids - DNA and RNA consist of nucleotides only. DNA and RNA function as genetic material.


A primary metabolite is a kind of metabolite that is directly involved in normal growth, development, and reproduction. Primary metabolites have identifiable functions and play known roles in normal physiological processes.

The analyses of plant, fungal, and microbial cells, contain thousands of compounds other than primary metabolites, e.g. alkaloids, flavonoids, rubber, essential oils, antibiotics, colored pigments, scents, gums, and spices. These are called secondary metabolites.

Many secondary metabolites are useful to ‘human welfare’ (e.g., rubber, drugs, spices, scents, and pigments). Some secondary metabolites have ecological importance.


Chemical compounds found in living organisms are of two types.

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