Biological Molecules

• Calculating pH from concentration:

  • pH = -log(H⁺)
  • pOH = -log(OH⁻)
• pH = power of hydrogen
• pOH = power of hydroxide
• pH + pOH = 14
• Acids release H⁺ ions when they dissociate (fall apart into separate ions) and alkalis release OH⁻ ions.

  e.g. H₂SO₄ (sulfuric acid) releases 2 H⁺ ions when it dissociates.
• To find the pH of an alkali, find the pOH using the formula and subtract the answer from 14.
• pH is equal to the negative logarithm (the power to which 10 must be raised) of the hydrogen ion concentration of a solution.
• pH example questions:

  • Determine the pH of a 0.010M HNO₃ solution.

  pH = -log(0.010) = -log(1.0 x 10⁻²) = -(-2.0) = pH 2

  • What is the pH of a 2.5 x 10⁻⁶M solution of HCl?

  pH = -log(2.5 x 10⁻⁶) = pH 5.6 (2 d.p.)

  • Calculate the pH of a 0.0010M NaOH solution.

  pH = -log(0.0010) = 3 = 14 - 3 = pH 11

  • What is the pH of a 0.020M Sr(OH)₂ solution?

  pH = -log(0.020) = 1.7 (2 d.p.) = 14 - 1.7 = pH 12.3
• Organic compounds are any compound containing carbon (C) and found in living organisms.
• Four major categories of organic compounds:

  • carbohydrates
  • lipids
  • proteins
  • nucleic acids
• Condensation reactions are used to join monomers by chemical bonds through the elimination of a water molecule.
• Covalent bonds are strong bonds created through the sharing of electrons.
• Hydrolysis is a reaction which separates a large molecule into smaller ones and consumes a water molecule as a reactant.
• A monomer is a small repeating unit from which larger molecules (polymers) are made
• An isomer is a molecule with the same molecular formula but a different structural arrangement.
• Dipole-dipole forces are attractive forces between the positive end of the polar molecule and the negative end of another polar molecule.
• Hydrogen bonding occurs when hydrogen atoms covalently bonded to highly electronegative elements like oxygen, nitrogen, fluorine, and sulfur form weak dipoles with other nearby electronegative atoms.
• Ionic bonds involve electrostatic attraction between oppositely charged ions.
• Catabolism is the breakdown of complex molecules into simpler ones to release energy.
• Metabolism is the sum of all reactions that take place inside the cell.
• Anabolism is the build-up of larger, more complex molecules from smaller, simpler ones, which requires energy.
• Scientists studied two species of North American seahorses. They thought that these two species were closely related.

  Describe how comparisons of biological molecules in these two species could be used to find out if they are closely related.

  • compare DNA;
  • sequence of bases;
  • compare same protein;
  • sequence of amino acids;
  • immunological evidence:
  • inject seahorse protein into animal;
  • obtain antibodies;
• What is the symbol for the functional group carbonyl?

  CO
• What symbol does the functional group hydroxyl have?

  -OH
• What symbol does the functional group carboxyl have?

  -COOH
• What symbol does the functional group amine have?

  -NH2
• What symbol does the functional group phosphate have?

  -OPO32
• What symbol does the functional group methyl have?

  CH3
• What symbol does the functional group sulfhydryl have?

  SH
• Describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers. Give two named examples of polymers and their associated monomers to illustrate your answer.

  • a condensation reaction joins monomers together and forms a chemical bond and releases water;
  • a hydrolysis reaction breaks a chemical bond between monomers and uses water;
  • examples include:
  • amino acid and polypeptide;
  • nucleotide and polynucleotide, DNA or RNA;
  • alpha glucose and starch/glycogen;
  • beta glucose and cellulose;
  • reference to a correct bond within a named polymer;
• What is a monomer?

  • a monomer is a smaller repeating unit from which polymers are made;