molecules

• There is a wide diversity in living organisms in our biosphere
• Elemental analysis of plant tissue, animal tissue or microbial paste reveals elements like carbon, hydrogen, oxygen and several others
• Elemental analysis of a piece of earth's crust also reveals a similar list of elements
• Differences between living tissue and earth's crust

  • The relative abundance of carbon and hydrogen is higher in any living organism than in earth's crust
• How to analyse chemical composition

  1. Grind living tissue in trichloroacetic acid

  2. Obtain filtrate (acid-soluble pool) and retentate (acid-insoluble fraction)

  3. Analyse acid-soluble pool for organic compounds

  4. Analyse acid-insoluble fraction for macromolecules
• Thousands of organic compounds are found in the acid-soluble pool
• Analytical techniques can identify the molecular formula and probable structure of compounds
• Biomolecules


  All the carbon compounds that we get from living tissues
• Living organisms also contain inorganic elements and compounds
• Determining inorganic content


  1. Weigh living tissue (wet weight)

  2. Dry the tissue to get dry weight

  3. Burn the dry tissue to get ash

  4. Ash contains inorganic elements and compounds
• Organic compounds found in living tissues

  • Amino acids
  • Nucleotide bases
  • Fatty acids
• Amino acids


  Organic compounds containing an amino group and an acidic group on the same carbon
• Amino acids


  • Based on the nature of R group, there are 20 types of proteinaceous amino acids
  • Have chemical and physical properties of the amino, carboxyl and R functional groups
  • Can be acidic, basic or neutral depending on the number of amino and carboxyl groups
  • Can be aromatic
• Lipids


  Generally water insoluble, can be simple fatty acids or more complex compounds with glycerol and fatty acids
• Nucleosides


  Nitrogen bases attached to a sugar
• Nucleotides


  Nucleosides with a phosphate group esterified to the sugar
• Nucleic acids like DNA and RNA consist of nucleotides
• Primary metabolites


  Biomolecules like amino acids, sugars etc. found in all living organisms
• Secondary metabolites


  Compounds like alkaloids, flavonoids, rubber, essential oils etc. found in plants, fungi and microbes, but not in all living organisms
• Primary metabolites have known functions in normal physiological processes, while the functions of secondary metabolites are not fully understood
• Many secondary metabolites are useful for human welfare (e.g. drugs, spices, pigments)
• Biomolecules have molecular weights ranging from 18 to around 800 daltons, while biomacromolecules have molecular weights of ten thousand daltons and above
• Lipids, despite having molecular weights less than 800 daltons, are found in the acid-insoluble fraction due to their arrangement into structures like cell membranes
• The acid-soluble pool represents the cytoplasmic composition, while the acid-insoluble fraction represents the macromolecules from cytoplasm and organelles
• Water is the most abundant chemical in living organisms