Chapter 11

• Rosalind Franklin


  Woman who first made good guesses about the shape of DNA
• Watson and Crick


  Men who filled in the details and won a Nobel Prize for giving us a complete picture of DNA
• Why DNA needs to be two strands of nucleotides


  Each strand needs to act like a template for building complementary DNA strands
• Semiconservative model


  Correct model of DNA replication
• Every new strand of DNA is part old, part new
• How DNA is packed up into chromosomes

  1. Double stranded DNA in every chromosome is wrapped around sets of eight histones proteins called nucleosome

  2. Making the DNA look like beads on a string

  3. Other histone proteins then bend the strand back and forth into 30-nanometer size

  4. Chromatin is then further coiled and condensed into the rod-shaped of our chromosomes
• Karyotype


  Organized image of the chromosomes from one metaphase cell
• Purpose of karyotype


  • Checks damaged chromosomes and/or aneuploidies
  • Checks for any incorrect number of chromosomes
• Why cells need to do DNA replication

  Cell division by mitosis and meiosis requires that the chromosomes be doubled beforehand
• Without DNA replication, cell division would decrease chromosome number by half with every cell division and gamete production by meiosis would not arrive at the correct haploid chromosome number
• Replication bubble


  What opens up at the origin of replication point in DNA
• Functions during DNA replication

  • Helicase
  • Single-strand binding proteins
  • Topoisomerase
  • Primase
  • DNA polymerases
• DNA strands are antiparallel
• DNA polymerase enzymes can only build new DNA in the 5 to 3 direction
• DNA polymerase requires an RNA primer to begin
• Leading strand


  New DNA can be made continuously on one side of a replication fork
• Lagging strand


  New DNA can only be made in pieces on the other side of a replication fork