Inorganic and Organic components of Life

  • A cell is composed of a variety of molecules called biomolecules.
  • The biomolecules determine the structure and function of different cells.
  • Aggregation of various types of such biomolecules in a cell is called cellular pool. The cellular pool is composed of both inorganic and organic molecules.
  • Biomolecules may either be macro molecules or micro molecules.
  1. Micro molecules:
  • They are the substrates and products of metabolism in a cell.
  • They include inorganic compounds like water, minerals and gases and organic compounds like sugars, lipids, amino acids and nucleotides.

Inorganic compounds:


  • It constitutes 60-70% of the cell contents and 75-90% of the protoplasm.
  • It is the most abundant compound in living organisms.


  • Minerals constitute about 1-3% of the cell contents but are very essential for life activities.
  • Essential minerals required in large quantities for proper growth and metabolism are called macronutrients. They include Ca, S, P, Mg, Fe and K.
  • Minerals required in small quantities are called micronutrients. They include Co, Mn, Zn, Mo and Cl.
  • Some minerals act as buffers and maintain acid base balance in the cell and extracellular fluid.


  • Gases form less than 0.5% of the cell contents.
  • They include O2, N2, CO2, NH3
  • These gases being soluble in water occur in dissolved state.

Organic compounds: Carbon containing compounds are called organic compounds and make up about 95% of the dry weight of the protoplasm or cell. It includes sugar, lipids, amino acids and nucleotides.


  • Carbohydrates constitute about 1% of the cell contents.
  • They are compounds of carbon, hydrogen and oxygen generally in the ratio of 1:2:1.
  • Glucose is the universal sugar and is also known as dextrose or grape sugar. It is the main source of energy in the cells and is the blood sugar in most of the animals.
  • Fructose is the fruit sugar and is also known as levulose. It is the sweetest among the naturally occurring sugars.
  • Maltose, sucrose and lactose are the common disaccharides.
  • Maltose or malt sugar is formed in germinating seeds.
  • Sucrose is the common cane or table sugar.
  • Lactose or milk sugar is found in mammalian milk.


  • The lipids constitute 3.5% of the cell contents.
  • They are C, H and O compounds with lesser proportion of oxygen.
  • They are insoluble in water and on oxidation yield maximum energy.
  • Lipids are the food reserves of plant and animals.
  • The fats form insulating layer under the body skin and help to conserve the body heat in animals.

Amino acids:

  • Amino acids are building blocks of proteins.
  • They are made up of C, H, O and sometimes S.
  • There are 20 amino acids which are normal components of proteins.
  • Animals cannot synthesize all the amino acids. They require some in readymade form in the food. Such amino acids are called essential amino acids. e.g. Lysine, Leucine, Valine, Tryptophan etc.


  • Nucleotides constitute about 2% of the cell contents.
  • The nucleotides polymerize to form nucleic acids like DNA and RNA.
  • Specific sequence of nucleotides in DNA codes for specific amino acids required for protein synthesis.
  • In addition with phosphate, nucleotides form energy carriers such as ADP and ATP.
  • Nucleotides take part in the formation of coenzymes by replacing their nitrogen base group with some vitamins.
  • NAD, NADP, FAD and coenzyme A are some important examples of coenzymes.
  1. Macromolecules:
  • Macromolecules have a complex molecular structure and occur in colloidal state.
  • They are insoluble in intracellular fluid and formed by polymerization of micro molecules.
  • They include only organic compounds such as polysaccharides, proteins and nucleic acids which are the polymers of sugars, amino acids and nucleotides respectively.


  • Polysaccharides consist of two or more units of sugars (Monosaccharides) which are joined together by glycoside bonds with a loss of a water molecule.
  • Homopolysaccharides: They consist of only one type of monosaccharides. E.g. Glycogen (chain of glucose) in animals, starch and cellulose (chain of glucose) in plants.
  • Heteropolysaccharides: They are composed of modified monosaccharides. They include mucopolysaccharides, glycoproteins and chitin.
  • Hyaluronic acid, Heparin, Chondroitin sulphate and Keratin sulphate are mucopolysaccharides.


  • Proteins constitute about 12% of the cell contents and form nearly 75% of the dry weight of most of the cells.
  • They are linear, unbranched polymers of amino acids.
  • They are structural basis of cells and help in the growth, repair and maintenance of the cells.
  • All enzymes, antibodies and some hormones are also proteins.

Nucleic acids:

  • Nucleic acids are strong acids mainly present in the nucleus and in lesser quantities in mitochondria, plastids and cytoplasm.
  • Nucleic acids are linear, unbranched polymers of nucleotides, hence also called polynucleotides.
  • DNA and RNA are the examples of nucleic acids.


  • It has adenine, guanine, cytosine and thymine as nitrogen bases.
  • It has the blue print for all the hereditary characters of an organism.
  • It has a double helical structure with two antiparallel strands held by H- bonds.


  • RNA has uracil instead of thymine, other nitrogen bases being similar to that of DNA.
  • They are single stranded and play a major role in protein synthesis.
  • They are of three types; ribosomal RNA (rRNA), messenger RNA (mRNA) and transfer RNA (tRNA).

Inorganic and Organic components of Life