1.1 + 1.2 - Structure and Replication of DNA

• A?

  phosphate

  
• B?

  deoxyribose sugar

  
• C?

  base

  
• How is the sugar and phosphate bonded in DNA structure?

  strong covalent bond
• How are the bases held together in DNA structure?

  weak hydrogen bond
• Leading strand runs from 5’ to 3’
• Lagging strand runs from 3’ to 5’
• DNA can be described as antiparallel
• Define DNA structure?

  a double stranded helix with anti parallel strands
• The base sequence of DNA forms the genetic code
• Adenine bonds to thymine
• Cytosine bonds to guanine
• What is a prokaryote?

  organisms that do not have a membrane bound nucleus (bacterial cells)
• What is a eukaryote?

  organisms that have a membrane bound nucleus (animal, plant, fungal)
• How is DNA arranged in prokaryotes ?

  • one circular chromosome
  • smaller circular plasmids to contain extra genes
• How is DNA arranged in eukaryotes?

  • linear chromosomes in the nucleus packaged with histones to prevent tangling
  • circular chromosomes in mitochondria and chloroplasts
  • yeast also has plasmids
• define dna replication ?

  process where DNA makes an identical copy of itself
• dna replication always precedes mitosis
• What 5 things are required for dna replication?

  DNA template

  enzymes (DNA polymerase)

  ATP

  DNA nucleotides

  Primers
• what is the function of a primer?

  to initiate DNA replication
• what is a primer?

  a short strand of nucleotides which binds to the 3’ end of the template DNA strand
• What is the first stage of DNA replication?

  double helix is unwound by the enzyme helicase
• stage 2 of DNA replication ?

  hydrogen bonds break between bases to form 2 template strands and a replication fork is formed
• A?

  leading strand

  
• B?

  lagging strand

  
• What direction does DNA polymerase add DNA nucleotides in?

  3’ to 5’
• the leading strand of DNA is replicated continuously
• The lagging strand of DNA is replicated in fragments
• why is the lagging strand replicated in fragments?

  DNA nucleotides must be added from the 3’ end
• What happens during stage 3 of DNA replication?

  primers initiate DNA replication by binding to the 3’ end of the leading strand and at several sites of the lagging strand
• What happens during stage 4 of DNA replication?

  DNA polymerase adds free DNA nucleotides continuously to the 3’ end of the lead strand in fragments to the 3’ end of the lag strand
• what happens during stage 5 of dna replication?

  fragments of DNA in lag strand joined together by ligase
• what is PCR (Polymerase chain reaction)?

  a laboratory technique used to amplify DNA using complimentary primers for specific target sequences
• What apparatus is used in PCR?

  Thermocycler
• What are the 3 stages of PCR?

  Denaturation, annealing, extension
• stage 1 of PCR?

  DNA is heated between 92 and 98 °C to separate the strands
• stage 2 of PCR?

  DNA is cooled to between 50 and 65 °C to allow primer to bind to target sequences
• stage 3 of PCR?

  DNA is heated to between 70 and 80 °C for heat-tolerant DNA polymerase to replicate the region of DNA
• A?

  DNA denaturation

  
• B?

  primer annealing