1.4.11 Describe DNA replication (including the role of DNA polymerase), and explain how Meselson and Stahl’s classic experiment provided new data that supported the accepted theory of replication of DNA and refuted competing theories.

Replication 

- The two strands of DNA unwind and split apart.

- The exposed bases attract the the free DNA nucleotides, they line up along each strand, observing the complementary bases pairing rules. 

- The enzyme DNA polymerase bonds the nucleotides together, forming a phosphodiester bond between each deoxyribose and a adjacent phosphate group. hydrogen bonding link the two strands together.

Meselson and Stahl's Classic Experiment

- A sample of bacteria was grown in a nutrient broth containing light nitrogen, and one on a broth with heavy nitrogen, as bacteria reproduced they took up nitrogen so it became a part of their DNA.

- A sample of DNA was taken from each batch of bacteria and spun in a centrifuge: the DNA from the heavy nitrogen bacteria settled lower down in the centrifuge tube than the DNA from the light nitrogen bacteria. 

- The bacteria grown in heavy nitrogen broth were taken out and put in a broth containing only light nitrogen.

- After one round of DNA replication another DNA sample was taken and spun in the centrifuge, it settled in the middle, showing that the new bacterial DNA molecule contained one strand of the heavy nitrogen and one strand of the light nitrogen; the bacterial DNA had replicated semi conservatively.