Biology

• When analysing markets, a range of assumptions are made about the rationality of economic agents involved in the transactions
• The Wealth of Nations was written

  1776
• Rational


  (in classical economic theory) economic agents are able to consider the outcome of their choices and recognise the net benefits of each one
• Governments act rationally by


  Placing the interests of the people they serve first in order to maximise their welfare
• Rationality in classical economic theory is a flawed assumption as people usually don't act rationally
• A water molecule is made up of one atom of oxygen and two atoms of hydrogen
• Water is a polar molecule


  The electrons are held closer to the oxygen atom (ᵹ-) than to the hydrogen atoms (ᵹ+)
• Hydrogen bonds

  Weak electrostatic attraction between the slightly negative oxygen atom of one water molecule and the slightly positive hydrogen atom of another water molecule
• Importance of water properties

  • Water is a polar solvent
  • Water is an excellent transport medium
  • Density of water reaches maximum at 4°C
  • High specific heat capacity
  • Incompressible liquid
  • Cohesive and adhesive
  • High surface tension
  • Amphoteric
• Carbohydrates


  Molecules composed of carbon, hydrogen and oxygen
• Types of monosaccharides


  • Triose sugars
  • Pentose sugars
  • Hexose sugars
• α-glucose and β-glucose


  Different forms of glucose - isomers
• Disaccharides


  Composed of 2 monosaccharides joined by a condensation reaction
• Glycosidic bond


  Covalent bond formed between the C1 of one monosaccharide and C4 of another
• Polysaccharides


  Made of many monosaccharide molecules linked by glycosidic bonds
• Starch


  • Composed of α-glucose
  • Mixture of amylose (unbranched) and amylopectin (branched)
• Glycogen


  • Similar structure to amylopectin but with more branching
• Test for starch


  1. Add iodine solution

  2. Blue-black colour indicates presence of starch
• Lipids


  Molecules composed of carbon, hydrogen and oxygen, with less oxygen than carbohydrates
• Fatty acids


  Long hydrocarbon chain with a carboxyl group (-COOH) at one end
• Saturated fatty acids


  • Carbon atoms joined by single covalent bonds, fully saturated with hydrogen
• Unsaturated fatty acids


  • Carbon chains have one or more double covalent bonds between carbon atoms
• Esterification


  Condensation reaction forming ester bonds between carboxyl group of fatty acids and hydroxyl group of glycerol
• Proteins


  Molecules composed of carbon, hydrogen, oxygen, nitrogen and often sulphur
• Amino acids


  Monomers of proteins, have an amino group (-NH2) and a carboxyl group (-COOH) attached to a carbon atom
• Forming proteins from amino acids

  Amino acids join by condensation reaction between amino group and carboxyl group, releasing water and forming a peptide bond
• Bonds in proteins


  • Peptide bonds, hydrogen bonds, disulphide bonds, ionic bonds
• Peptide bond formation


  1. Release of a water molecule

  2. R group is not involved
• Main bonds in proteins

  • Peptide bonds
  • Hydrogen bonds
  • Disulphide bonds
  • Ionic bonds
• Hydrogen bonds


  • Formed between the tiny negative charges on the oxygen of the carboxyl groups and the tiny positive charges on the hydrogen of the amino groups
  • They break and re-form with changes in pH and temperature
• Disulphide bonds


  • Formed between sulphur atoms of 2 cysteine molecules when closely related
  • A strong covalent bond that holds the folded polypeptide chains in place
• Ionic bonds


  • Form between the strongly positive and negative amino acid side chains (R groups) found deep in the protein molecule
  • Strong uncommon bonds
• Levels of protein structure

  • Primary structure
  • Secondary structure
  • Tertiary structure
  • Quaternary structure
• Primary structure

  • Linear sequence of amino acids held by peptide bonds
• Secondary structure


  • Polypeptide chains of repeated structure held by hydrogen bonds
  • α-helix (a spiral coil)
  • β-pleated sheet in which the polypeptide chain folds into regular pleats held together by hydrogen bonds
• Tertiary structure


  • 3D organization imposed on the secondary structure where the amino acid chain including α-helices and β-pleated sheets is folded further into a complicated shape
  • Hydrogen bonds, disulphide bonds and ionic bonds hold the 3D shapes in place
• Quaternary structure


  • Composed of several tertiary polypeptide chains giving 3D shape
  • The 3D shape is disrupted and denatured by any change in pH and temperature
• Examples of quaternary structure


  • Enzymes
  • Haemoglobin
• Fibrous proteins


  • They are of secondary structure
  • They are long parallel polypeptide chains with cross-links that form into fibers
  • They are insoluble in water and extremely tough
  • They appear in the structure of connective tissue, tendons, matrix of bones, muscles and keratin that forms hair, nails, horns and feathers
• Collagen


  • Extremely strong with tensile strong fibers
  • 3 polypeptide chains, each is made up of 1000 amino acids
  • The primary structure of these chains shows the repetition sequence of glycine with 2 other amino acids (proline and hydroxyproline)
  • The three α- chains are arranged in a triple helix form held together by hydrogen bonds