1 - Biological Molecules


1 - Biological Molecules

  • the study of biological molecules is known as molecular biology

1.1 - introduction to biological molecules

Bonding and the formation of molecules:

  • atoms share a pair of electrons in their outer shells
  • as a result of this sharing, the outer shell of both atoms is filled and a molecule is formed

ionic bonding -

  • ions with opposite charges attract to one another; this electrostatic attraction is known as an ionic bond
  • ionic bonds are weaker than covalent bonds
  • example : sodium chloride of Na+ and Cl-


  • electrons within a molecule are not evenly distributed but tend to spend more time at one position
  • the region where these electrons are distributed, is more negatively charged than the rest of the molecule

polar/polarised molecule: a molecule with an uneven distribution of charge

hydrogen bonding -

  • when the negative region of one polarised molecule and the positively charged region of another attract each other and a weak electrostatic bond is formed between the two
  •  each bond is individually weak, however they can collectively form important forces that alter the physical properties of molecules
  • an example is - water

polymers - long chain of monomers sub-units

polymerisation - the process in which polymers are formed

  • the monomers of a polymer are usually based on Carbon

polythene and polyesters - industrially produced

polysaccarides, polypeptides and polynucleotides - made naturally by living organisms

  • the basic sub-unit of a polysaccaride is a monosaccaride or single sugar i.e glucose

polynucleotides -

  • formed from mononucleotide sub-units

polypeptides -

  • formed by linking together peptides that have amino acids as their basic sub-units

Condensation and Hydrolysis reactions:

  • in the formations of polymers by polymerisation in organisms, each time a new sub-unit is attached a molecule of water is formed
  • condensation reactions - reactions that produce water
  • the formation of a polypeptide from amino acids = condensation reaction
  • the reaction of a polysaccharide starch from the monosaccharide glucose = condensation reaction
  • polymers can be broken down by through the addition of water
  • hydrolysis reactions - when water molecules are used when breaking the bonds that link the sub-units of a polymer , splitting the molecule into its constiuent parts
  • hydro = water
  • lysis = splitting
  • polypeptides can be hydrolysed to amino acids
  • starch can be hydrolysed to glucose

Reactions between substances:

  • nucleotides --> polynucleotides (nucleic acids) = condensation
  • polynucleotides --> nucleotides = hydrolysis
  • monosaccarides -->polysaccharides (carbohydrates) = condensation
  • polysaccharides (carbohydrates) --> monosaccharides = hydrolysis
  • fatty acids --> lipids = condensation
  • lipids --> fatty acids = hydrolysis
  • glycerol -->lipids = condensation
  • lipids --> glycerol = hydrolysis
  • amino acids --> polypeptides (proteins) = condensation
  • polypeptides (proteins)--> amino acids = hydrolysis

metabolism - all the chemical processes that take place in living organisms 

the mole - the SI unit for measuring the amount of substance

1 mole = the same number of particles as there are in 12g of Carbon-12 atoms this number is the avogandro constant and is 6.022 x 10 to the power of 23

molar solution


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