Replication of DNA:

I. Definiton- a process in which DNA is copied in order to provide the appropriate number of chromosomes to the cells that result from cell division

II. Replication occurs in the nucleus of eukaryotic cells.

Image of replicating DNA credited to:

III. DNA is put together in an anti-parallel fashion.
  • The carbons in a deoxyribose sugar are numbered. The 5' end of the DNA chain is essentially the end that has the phosphate group sticking out. The 3' end appears to be the "bottom" of the sugar birdhouse.
external image moz-screenshot.jpgexternal image moz-screenshot-1.jpg3'_and_5'

Above image of DNA credited to:

  • DNA replicates quickly and easily when it moves from 5' to 3'. (meaning when new nucleotides are attached to the 3' end of a strand)
  • The leading strand is the strand on which DNA can replicate from 5' to 3'.
  • The lagging strand takes longer because DNA cannot replicate easily in this fashion.

IV. Enzymes Involved:
  • helicase- opens the hydrogen bonds that hold the base pairs together
  • DNA polymerase- lays down the new DNA nucleotides to create the new strands
  • RNA primase- aids DNA polymerase by laying down short sections of RNA for DNA polymerase to work off of

V. The Lagging Strand:
  • Requires the assistance of RNA primase so DNA nucleotides can be linked in a 5' to 3' fashion
  • Replicates more slowly than the leading strand

VI. General Overview and Terminology:
  1. When a cell is preparing to divide, the DNA must replicate.
  2. Helicase breaks the H bonds to form several replication forks down the length of the chromosome.
  3. DNA polymerase brings in complementary nucleotides to link to the original nucleotides on each side of the parent DNA strand.
  4. Because replication is semi-conservative, each DNA molecule created has an original parent strand and a newly synthesized daughter strand.
  5. The two DNA molecules are considered to be sister chromatids held together at their centromere.
  6. They will be separated during the process of cell division so each cell receives a copy of every chromosome.
Fabulous Animation of Replication and the Structure of the Helix