Biomolecules

• Organisms


  Composed of about 25 chemical elements
• Most abundant elements in the human body

  • Oxygen
  • Carbon
  • Hydrogen
  • Nitrogen
• Atom


  The smallest particle of a chemical element that can exist
• Any substance that has mass and occupies space is matter
• All matter is composed of extremely small particles called atoms
• Atoms


  Electrically neutral overall since number of protons = number of electrons
• Atoms making up an element have a specific number of protons
• Molecule


  Formed when 2 or more atoms of an element chemically join together

  
• Compound


  A molecule composed of two or more different atoms
• Chemical Bonds


  Hold atoms together in molecules or compounds
• Ways atoms can interact to form chemical bonds

  • Gaining electrons
  • Losing electrons
  • Sharing electrons

  
• Types of chemical bonds

  • Covalent bond
  • Ionic bond
  • Hydrogen bond

  
• Covalent bond


  Enables formation of molecules by joining atoms together through sharing of electrons

  
• Sharing of electrons


  Can be equal (nonpolar covalent bonds) or unequal (polar covalent bonds)
• Ionic bond


  Formed by electrical attraction of positive and negative ions
• Hydrogen bond


  Relatively weak bond formed by attraction of an atom carrying a slight positive charge (hydrogen) and another atom carrying a slight negative charge (oxygen)

  
• Basis of interaction and strength of different chemical bonds

  • Covalent bond: Sharing of electrons, Strong
  • Ionic bond: Attraction of opposite charges, Strong
  • Hydrogen bond: Sharing of H atom, Weak
  • Hydrophobic interaction: Forcing of hydrophobic portions of molecules together in presence of polar substances, Weak

  
• Water is a vital chemical of living cells
• Life started in water and all living cells and organisms contain water
• Water makes up 70% of the earth's surface, 80% of a plant, and 60% of the human body
• Water molecule


  Consists of an oxygen atom bound to two hydrogen atoms by two single covalent bonds

  
• The water molecule is stable and V-shaped with an angle of 104.5 degrees due to the lone pairs of electrons on the oxygen atom

  
• The water molecule is electrically neutral overall since it has no unpaired electrons
• The shared electrons in the covalent bonds of the water molecule are drawn closer to the oxygen atom than the hydrogen atoms, as oxygen is more electronegative
• Oxygen end of water molecule

  Has a slight negative charge (δ-)

  
• Hydrogen end of water molecule

  Has a slight positive charge (δ+)

  
• The water molecule is a dipolar molecule
• Hydrogen bond


  Forms between polar covalent compounds like water, where charged areas attract each other

  
• Hydrogen bonds are individually very weak, but the cumulative effects of large numbers of these bonds can be enormous
• Unique properties of water due to hydrogen bonding

  • Ice floats
  • Water can stick to itself (cohesion)
  • Water can stick to things (adhesion)
  • It is an excellent solvent

  
• Factors that give water its unique properties

  • Shape of the water molecule
  • Polar nature
  • Ability to form hydrogen bonds

  
• Chemical and physical properties of water

  • Makes up 60 to 90% of the fresh mass of an organism
  • Is an excellent solvent for polar substances
  • Is an excellent medium for diffusion or other processes
  • It is a reagent that takes part in reactions such as hydrolysis
  • It gives support, mainly to aquatic organisms
• Water properties related to plants

  • It is one of the reagents in photosynthesis
  • Seed germination commences with the splitting of the testa after water is imbibed
  • Transpiration and translocation depend on water
  • Water enters a plant cell via osmosis and this is important for cell enlargement and supports the guard cell mechanism
• Water properties related to animals

  • Water takes part in internal and external transport, e.g. digestion
  • Osmoregulation
  • Cooling by evaporation in sweating and panting
  • Lubrication as in joints, mucus, pleural fluid and pericardial fluid
  • For support, e.g. hydrostatic skeletons
  • Protection - it is an important constituent of mucus
  • Serves as a means of migration in ocean currents, e.g. Salmon
• Biological significance of water

  • Nature of water
  • Solvent properties
  • High specific heat capacity
  • High heat of fusion
  • High heat of vaporisation
  • High density of water
  • High surface tension
  • Low viscosity
  • Water as a reactant
• Nature of water


  Water is a liquid at room temperature due to hydrogen bonding, which makes it a significant liquid in which organisms may live and provides a liquid environment inside cells where biochemical reactions can occur

  
• Solvent properties


  Water is an excellent solvent for polar and charged molecules (hydrophilic) but repels uncharged and non-polar molecules (hydrophobic); it acts as a transport medium and universal solvent
• High specific heat capacity

  A large increase in heat energy will result in a small rise in temperature, helping to maintain a constant temperature in aquatic environments and in large organisms
• High heat of fusion

  Prevents cell contents and aquatic environments from freezing rapidly in low temperatures
• High heat of vaporisation


  Causes a pronounced cooling effect during sweating, panting and evaporative cooling as the energy is being taken up by water