DNA replication

• DNA gyrase unwinds the double helix
• DNA helicase breaks (unzips) hydrogen bonds between the nucleotide bases, resulting in two single strands of DNA with exposed nucleotide bases.
• the enzyme DNA polymerase catalyses the addition of new nucleotide bases, in the 5' to 3' direction, using the unzipped DNA as a template, free phosphorylated nucleotides, present in the nucleoplasm within the nucleus, are bonded to the exposed bases, following complementary base-pairing rules
• the leading strand is synthesised continuously from the 3' to 5' direction, whereas the lagging strand is in fragments (discontinuous)
• the breaks on the lagging strand are later joined by ligase enzymes
• the activated nucleotides then undergo a hydrolysis reaction, to release the extra phosphate group, this supplies the energy to make phosphodiester bonds between the sugar residue of one nucleotide and the phosphate group of the next nucleotide.
• There were three theory's for DNA replication, conservative (the original molecule acts as a template and a new molecule is made), dispersive (the original molecule breaks up into nucleotides. each one joins to a complementary nucleotide and new ones join up again), semi-conservative (the new molecule consists of one original strand and one newly formed strand.)