3.1.5.2 Replication

• DNA undergoes semi-conservative replication, where each new strand is made from the original strand and a new strand. This ensures genetic continuity in each new generation of cells produced so they can continue to carry out the same function.
• Semi-conservative replication

  1. DNA helicase unwinds DNA and breaks the hydrogen bonds between the specific base pairs in the parents DNA molecule
  2. New nucleotides in the nucleus are attracted to the exposed bases on both template strands and new hydrogen bonds form
  3. DNA polymerase joins the sugar-phosphate backbones of the new strands, by creating new phosphodiester bonds between adjacent nucleotides.
  4. Each new DNA molecule has one old parent strand and one newly synthesised strand
• Evidence for semi-conservative replication

  Bacteria cultured in 15N is centrifuged, making one low band in the tube. The same bacteria is then cultured for one cycle of division in 14N, making one band of 14N in the middle of the tube. When cultured in 14N for another cycle two bands are formed, one at the top and one in the middle.