Biological Molecules

• Condensation reaction


  A reaction that occurs when 2 molecules are joined with removal of water
• Hydrogen bond


  A weak interaction that can occur when a molecule has slight negative charged atom bonded to a slight positive hydrogen atom
• Hydrolysis reaction


  Reaction that occurs when a molecule is split into 2 smaller molecules with addition of water
• Monomers


  Smaller units from which larger molecules are made, e.g. monosaccharides, amino acids, nucleotides
• Polymers


  Larger molecules made from many monomers, e.g. polysaccharides, polypeptides, proteins, DNA, RNA
• Water


  • Solvent
  • High specific heat capacity
  • Latent heat of evaporation
  • Cohesion and adhesion
  • Density
• Water as a solvent

  Water is polar and so ions and polar covalent substances dissolve in it, allowing chemical reactions to occur in cells as solutes are more chemically active when free to move, and metabolites to transport efficiently
• High specific heat capacity of water

  Due to many hydrogen bonds, more energy is required to break and build bonds so temperature does not fluctuate much, therefore, suitable habitat as able to maintain constant temperature (optimal for enzyme activity), and water in blood plasma vital for transferring heat around body, maintain temperature
• Latent heat of evaporation of water

  More energy required to change state from liquid to gas as lots of energy must be absorbed by water to break hydrogen bonds without them reforming, good so little water required to evaporate for organism to be heated, providing cooling effect
• Cohesion and adhesion of water

  Hydrogen bonds between molecules allow for strong cohesion between molecules, allowing for continuous stream of water, and enables surface tension where water meets air, hydrogen bonds also allow water to 'stick' or bond to other molecules, e.g. cellulose which is adhesion (enables water to move up xylem)
• Density of water


  When water cools, uniquely, it gets less dense as its solid state is a lattice, due to hydrogen bonds which are extended, therefore creating a less dense structure, useful so top of pond when frozen doesn't sink, rather, is an insulator
• Cations


  • Calcium, Ca⁺
  • Sodium, Na⁺
  • Potassium, K⁺
  • Hydrogen, H⁺
  • Ammonium, NH₄⁺
• Anions


  • Nitrate, NO₃⁻
  • Hydrogencarbonate, HCO₃⁻
  • Chloride, Cl⁻
  • Phosphate, PO₄³⁻
  • Hydroxide, OH⁻
• Deficiency


  Some required in large amounts (macronutrients, main elements), some in small amounts (micronutrients or trace elements), can display deficiency if lack of an ion, e.g. low cobalt = anaemia, low copper = young shoots die back