DNA replication

• Function of DNA: Heritable


  Genetic material can be passed to offspring
• Function of DNA: Used to Compare


  DNA very similar in different organisms of the same species and less similar in different species - the more similar the DNA, the closer relation between animals
• Functions of DNA: Stores a code


  The sequence of nucleotides contains a code in segments called genes
• Function of DNA: Replication


  Complementary bases enable DNA molecule to be replicated
• Purpose of DNA replication

  To duplicate the code it carries. The code can then be passed to daughter cells. 

  In eukaryotic cells, the chromosomes gain a sister chromatid and become double-stranded. DNA replication occurs in the preparation for all cell division, whether mitosis or meiosis
• When does DNA replication occur?

  During the S phase of interphase in the cell cycle
• Process of DNA replication: Step 3 


  Complementary nucleotides are added by the enzyme DNA polymerase. Synthesis of the new daughter strand is in a 5’ to 3’ direction. Adenine pairs with thymine, and cytosine pairs

  with guanine.
• Process of DNA replication: Step 1


  DNA helicase (enzyme) unwinds and separates the double strand by breaking the weak hydrogen bonds. Each half of the parent molecule is used as a template.
• Process of DNA replication: Step 2


  The enzyme primase attaches a short sequence of RNA, known as a primer, to show DNA polymerase where to start adding nucleotides.
• Process of DNA replication: Step 4


  
  

  The result is the production of two identical DNA molecules that are each made of one parent strand and one new daughter strand. Therefore, the process is described as semi-conservative.
• Synthesis: Leading Strand


  Synthesis along the leading strand is continuous - no okazaki fragments required
• Synthesis: Lagging Strand


  Primers are attached at short intervals, starting from the replication fork. DNA polymerase synthesizes short strands of new DNA called Okazaki fragments. DNA polymerase moves in opposite directions on the two anti-parallel parent strands.
• Steps of DNA replication: Step 5


  In eukaryotic organisms, two sister chromatids are now ready for cell division. In prokaryotes, two circular chromosomes are now ready for binary fission.