Describe the process of DNA replication in eukaryotic cells.

DNA replication occurs in the nucleus of the cell. DNA is first unwound to expose the nucleotides. This is is catalysed by DNA helicase which catalsyes the breakage of the hydrogen bonds between complimentary bases (adenine pairs with thymine, guanine pairs with cytosine). Primase then synthesises a small section of RNA around 6-10 bases long that is complimentary to the beginning of the DNA template strand. The role of the RNA primer is that it allows DNA polymerase to bind. Free nucleotides in the nucleus of the cell are then arranged to form a new strand of DNA that is complimentary to the template strand of the parent DNA molecule. It is this process that relies on DNA polymerase that catalyses the phospodiester bonds between bases that form the phosphosugar backbone of DNA. A secondary role of DNA polymerase is that it ensures high fidelitiy of replication. This is due to its exonuclease activity. If an incorrect base has been inserted into the newly synthesised strand, for example C instead of T to pair with A, it removes the incorrect base and reinserts the correct one. DNA replication is a semi-conservative process that was demonstrated by the Meselson and Stahl experiement using heavy nitrogen that showed that each new daughter molecule of DNA contains one strand from the parent molecule and one newly synthesised strand.