1.3.1. Inorganic Biomolecules


1) Quantitative importance:

  • It’s the most abundant substance in the biosphere and the largest component of living beings: between 65 and 95% of the weight of most living forms is water.
  • Some bodies and beings come to have a water content close to 90%, such as jellyfish.
  • The content of water varies with the age of individuals
  • If the water content decreases below some levels, vital functions will slow down or even stop.

2) Qualitative importance

  • The liquid water was on life support where it originated and where they develop biological processes.
  • The evolution has been influenced by the need to maintain a living aqueous environment (internal environment).
  • Water has extraordinary physical and chemical properties that are responsible for its biological importance.

Until the eighteenth century, water was regarded as a single body. In 1781 the English chemist Joseph Priestley made ​​his synthesis of hydrogen combustion. Later Antoine-Laurent Lavoisier and Henrv Cavendish showed that water consisted of hydrogen and oxygen and then in 1805, the French chemist Joseph Louis Gay-Lussac and wise Alexandei-Prussian von Humboldt showed that the hydrogen ratio / oxygen was equal to 2, which led to the molecular formula H2O.

The water molecule consists of two hydrogen atoms and one oxygen.

Water is characterized by their extraordinary physicochemical properties. Living beings have adapted to use chemically into two types of reactions:

  1. Enzymes as a source of electrons and hydrogen atoms, for example photosynthesis.
  2. Enzymatic hydrolysis, breaking links to degrade complex organic compounds into simpler others, as in breathing.

Water is the chemical substance with chemical formula H2O: one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom. Because of water’s electronic structure, the oxygen atom has a slight negative charge on it and the hydrogen atoms are slightly positive. When water molecules are close together, their positive and negative regions are attracted.  These attractive forces are known as hydrogen bonds. Hydrogen bonds are the reason for water’s very special properties which make life on Earth possible.

Water is a unique liquid, consists of H2O molecules tetrahedral geometry: two covalent OH and two doublets electronic free the oxygen atom pointing to the vertices of a tetrahedron in the center of which is oxygen.

Hydrogen bonds, formed between the dipoles of the molecule groups originate from 3 to 9 molecules. This enables high molecular weights and water behaves like a liquid. These groups, give the water its properties of fluid, in fact, liquid water, these small water polymers coexist with isolated molecules.

  • Water is the only natural substance that is found as a gas (water vapour), a liquid and a solid (ice) on Earth.
  • Density is a measure of how compact a substance is.  It is defined as the mass of a substance divided by its volume.  Solids are almost always the most dense form of a substance, then liquids and then gases.  As temperature increases, the density generally decreases.  Pure water is an exception to this and is the only substance which has its highest density as a liquid.  Water is at its most dense at about 4 oC.  This is because hydrogen bonds between water molecules give ice a very stable open ordered structure.  At low temperatures, water has a higher density than ice and this means that ice floats.

  • Water has a very high specific heat capacity. This means that a lot of energy is needed to increase its temperature (energy is needed to overcome the hydrogen bonds).  This allows the aqueous cytoplasm serve as protection against temperature changes. As the Earth is 71% water, energy from the sun causes only small changes in the planet’s temperature. This stops the Earth getting too hot or too cold and makes conditions possible for life. Heat is stored by the ocean in summer and released back to the atmosphere in winter. Oceans, therefore, moderate climate by reducing the temperature differences between seasons.
  • Water also has a high heat of vaporisation.  This means a lot of energy from the sun is needed to turn liquid water into vapour. As water vapour moves from warm areas to cooler regions it changes back to a liquid and may form rain. This releases heat which warms the air. The enormous amount of energy involved powers the storms and winds on Earth.
  • High cohesive force. Hydrogen bonds hold water molecules together tightly, forming a compact structure that makes it an almost incompressible fluid. Unable to be compressed in some animals can function as a hydrostatic skeleton.
  • Many substances dissolve in water and are stabilised by the hydrogen bonds. This allows the transport of oxygen, carbon dioxide, nutrients and waste materials in water and makes biological processes possible.
  • Because oil molecules are large and not electrically charged, they can’t be broken down into smaller charged molecules and be stabilised by water.  This means that they do not dissolve in water.


Like the vitamins do not provide energy but fulfill other functions:

  • Part of skeletal structures (shells, bones) and dental (calcium, phosphorus, magnesium and fluoride).
  • Regulate the balance of water inside and outside the cell (electrolyte).
  • Involved in nervous excitability and muscular activity (calcium, magnesium).
  • Allow the entry of substances into cells (glucose needs sodium to be able to be used as an energy source in cellular level).
  • Collaborate on metabolic processes (chromium is necessary for the functioning of insulin, selenium participates as an antioxidant). Involved in the proper functioning of the immune system (zinc, selenium, copper).
  • In addition, part of large molecules such as hemoglobin in the blood and chlorophyll in plants.

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