topic 1

• DNA replication occurs within the cell cycle before cell division which would either be mitosis or meiosis
• DNA replication happens in the S phase (synthesis phase) of interphase in the cell cycle
• Semiconservative replication


  One strand of the daughter DNA is from the parental DNA and one strand is newly synthesized
• Complementary base pairs


  • Adenine only bonds with thymine
  • Cytosine only bonds with guanine
• DNA helicase


  Breaks the hydrogen bonds between the complementary bases of the two DNA strands, causing the double helix to unwind and separate
• DNA polymerase


  Catalyses the condensation reactions to join adjacent nucleotides and create the phosphodiester bonds, forming the new polynucleotide chain
• DNA replication process


  1. DNA helicase breaks hydrogen bonds between complementary bases

  2. Separated strands act as templates

  3. Complementary nucleotides align opposite template strands

  4. DNA polymerase joins adjacent nucleotides via condensation reactions
• The new DNA has one original parental strand and one newly synthesized strand
• Complementary base pairing


  Enables identical copies of DNA to be created and reduces copying errors that would result in mutations
• Nitrogenous bases


  • Adenine
  • Cytosine
  • Guanine
  • Thymine
• DNA replication is a semiconservative process
• The Meselson and Stahl experiment proved the semiconservative replication of DNA
• Dipolar molecule


  Molecule with two different regions that are charged
• Water


  • 60-70% of body is made up of water
  • Oxygen has a slight negative charge
  • Hydrogens have a slight positive charge
  • Can form hydrogen bonds between oxygen and hydrogen of neighboring water molecules
• Properties of water


  • Metabolite
  • Solvent
  • High heat capacity
  • Large latent heat of vaporization
  • Strong cohesion
• Water as a metabolite

  1. Involved in chemical reactions like photosynthesis, photolysis, hydrolysis, condensation

  2. Approximately 90% of plasma in blood is water
• Hydrolysis reaction


  Polysaccharide + water -> separate into monomers
• Water as a solvent

  • Ability to dissolve many substances
  • Dissolves polar molecules due to attraction between water's charges and solute charges
  • Cannot dissolve non-polar molecules like lipids (hydrophobic)
• High specific heat capacity of water

  • Requires a lot of energy to raise the temperature of water
  • Helps maintain relatively stable temperatures in bodies of water and organisms
• Large latent heat of vaporization

  • Requires a lot of energy to convert liquid water to water vapor
  • Provides a cooling effect for animals (sweating) and plants (transpiration)
• Strong cohesion of water


  • Water molecules stick together due to hydrogen bonds
  • Allows continuous column of water to be pulled up xylem in plants
  • Provides surface tension for organisms to live on water surface