1.2

• DNA


  Made up of repeating units called nucleotides
• Nucleotide


  • Composed of a phosphate, a deoxyribose sugar and a base
• Structure of DNA


  1. Nucleotides joined by sugar phosphate bonds forming a sugar phosphate backbone

  2. Complementary base pairing between bases: Adenine-Thymine, Guanine-Cytosine

  3. Bases held together by hydrogen bonds

  4. DNA has an antiparallel structure with deoxyribose sugar at 3' end and phosphate at 5' end

  5. Strands form a double helix
• The base sequence of DNA forms the genetic code
• DNA Replication


  1. DNA double helix is unwound and hydrogen bonds between bases are broken to form 2 template strands

  2. DNA Polymerase (enzyme) requires a primer to start replication, primer binds to 3' end of template strand

  3. DNA Polymerase adds nucleotides using complementary base pairing to 3' end of new strand, leading strand replicated continuously, lagging strand replicated in fragments

  4. Fragments joined by ligase enzyme
• Two identical daughter DNA molecules are formed, each with one original and one newly synthesized strand
• Primer


  Short strand of nucleotides that binds to 3' end of template DNA strand
• DNA Polymerase


  Enzyme that adds nucleotides to 3' end of template DNA strand
• Leading strand


  Replicated continuously
• Lagging strand


  Replicated in fragments
• Ligase


  Enzyme that joins fragments of lagging strand
• Polymerase Chain Reaction (PCR)

  1. Amplification of DNA in vitro

  2. Primers are short strands complementary to target DNA sequences at 3' ends

  3. DNA heated to 92-98°C to separate strands

  4. Cooled to 50-65°C to allow primers to bind

  5. Heated to 70-80°C for heat-tolerant DNA Polymerase to replicate DNA

  6. Repeated heating and cooling cycles amplify target DNA region
• Amplification is the term used to describe production of multiple copies of DNA using PCR
• DNA Polymerase adds nucleotides to 3' end of template DNA strand
• Practical applications of PCR

  • Solve crimes
  • Settle paternity suits
  • Diagnose genetic disorders
• The 2 parent (template) strands are present in each generation after PCR
• Polymerase Chain Reaction (PCR)


  Technique for amplification of DNA in vitro
• Steps in Polymerase Chain Reaction

  • Heat DNA to 92-98°C to separate strands
  • Cool to 50-65°C to allow primers to bind
  • Heat to 70-80°C for DNA Polymerase to replicate DNA