2.1.2 Biological Molecules

• Water's polarity

  Polar molecule due to uneven distribution of charge; oxygen is more electronegative than hydrogen. Makes water a good solvent; it can form electrostatic interactions with other polar molecules and ions.

  
• Water in reactions

  Can act as a metabolite in reactions such as condensation and hydrolysis. Can act as a buffer because of its high SHC; minimises its temperature fluctuations.
• Water's density

  Maximum density of water is 4*C
• Density of ice vs. density of water

  Ice is less dense than water so can float on top; creates an insulating layer preventing animals living in water from freezing - water can act as a habitat.
• Water and Latent Heat of Vaporisation

  Has a high Latent Heat of Vaporisation; strong hydrogen bonds which gives the evaporation of water provides a cooling effect through sweating (little H2O is lost) and prevents dehydration in transpiration.
• Incompressible

  Water in incompressible; provide good support. For example a hydrostatic skeleton for small animals and gives turgidity to plant cells.
• Cohesion of Water

  Strong hydrogen bonds give water strong cohesive forces and hence, high tensile strength. Strong cohesion is good for supporting columns of water; high surface tension slows water loss through transpiration.
• Cohesion

  Refers to the attraction of one water molecule to another.
• Condensation Reaction

  Forms bonds; water is produced.
• Hydrolysis Reactions

  Breaks bonds; water is added to break bonds.
• Monomer

  Smaller units that join together to form large molecules (e.g. monosaccharides, amino acids, nucleotides)
• Polymer 


  Molecules formed when many monomers joing together, e.g. polysaccharides, proteins, DNA/RNA.
• Macromolecules

  Large and complex molecules that are formed due to the polymerisation of smaller monomers.
• Carbohydrates

  Contain the elements C,H,O. Have three types; mono, di, and polysaccharides.
• Monosaccharides

  Simplest carbohydrate, can't be hydrolysed.
• Glucose

  Glucose is a monosaccharide and is the main substrate for respiration. Has two isomers.
• Disaccharides

  Two monosaccharides joined by a glycosidic bond.
• maltose —> two glucose molecules

  sucrose —> glucose + fructose

  lactose —> glucose + galactose
• Alpha Glucose vs Beta Glucose

  Hydroxyl (OH) is on the bottom in alpha glucose, at the top in beta glucose.
• Glycosidic bonds


  Covalent bond formed due to a condensation reaction to make di and polysaccharides.
• Polysaccharides


  Formed from many glucose units joined togther
• Glycogen

  Formed from the condensation of alpha glucose; joined together by 1,4 and 1,6 glycosidic bonds.
• Properties of glycogen

  Branched; easily hydrolysed so glucose (hence energy) can be released quickly. Large but compact; maximises energy it can store. Insoluble; doesn't affect water potential and doesn't diffuse out of cells.
• Starch

  Mixture of two polysaccharides; amylopectin and amylose. Highly compact and stores energy.
• Amylose

  Unbranched, 1-4 glycosidic bonds, coiled, very compact (stores lots of energy).
• Amylopectin

  Branched, 1-4 and 1-6 glycosidic bonds, branches for rapid digestion by enzymes to release energy quickly.
• Cellulose

  Polymer of beta glucose that gives rigidity to plant cell walls. Has 1-4 glycosidic bonds in a unbranched, straight chain; alternate beta glucose molecules are rotated 180* to form these bonds. Hydrogen bonds form between parallel molecules to form microfibrils (high tensile strength) - helps them withstand osmotic pressure, and are freely permeable.
• NO3-

  Used in DNA, amino acids, NADP (photosynthesis), NAD (respiration)
• NH4+

  Can be converted to NO3- during the nitrogen cycle. Produced by the deamination of amino acids in the liver.
• OH-

  Affects pH and interacts with bonds in proteins to cause denaturation.
• (PO4)3-

  Component of ATP/ADP for energy release, and NADP.
• Na+ and K+


  Generates nerve impulses. Na+ is involved in co-transport mechanisms.
• Cl-

  Keeps the pH of the blood constant in gas exchange.
• H+

  Regulates pH
• H+ and HCO3-


  Forms in organisms when CO2 dissolves in water
• Ca2+

  Physiological functions, insulin release, nerve impulse transmission.
• Triglycerides

  Form from a condensation reaction between a glycerol and three fatty acid chains, forming an ester bond. Broken down by hydrolysis. Only soluble in organic solvents, e.g. alcohols.
• Saturated Triglycerides

  Contain only single bonds; straight chain molecules with many contact points. Have higher melting points (solid at room temperature), found in animal fats.
• Unsaturated Trigylcerides

  Contain C=C double bonds, causing kinks. Hence, less points of contact, lower melting points (weaker IMF's) so are liquid at room temperature. Found in plant oils.
• Formation of Triglycerides

  Glycerol undergoes condensation reaction with three fatty acid chains, forming triglyceride and a bi-product of 3H2O.