Stages

• 1 - Two polynucleotide strands of the original DNA molecule unwind out of the double helix (catalysed by enzyme DNA helicase) and the hydrogen bonds between the nitrogenous bases break (happens naturally)
• 2 - The two strands separate from each other (like a zip), each now acts as a template for the formation of a new strand; free DNA nucleotides join the exposed bases by complementary base pairings
• 3 - As the nucleotides line up they form a growing chain, and two of the phosphate groups from each nucleotide are removed by hydrolysis reactions; releasing energy to form phosphodiester bonds between the nucleotides
• 4 - DNA polymerase catalyses the bond formation between nucleotides, in a 5’ to 3’ direction only; so the new 3’ to 5’ strand is formed in short segments (5’ to 3’direction), called Okazaki fragments, by DNA ligase
• 5 - DNA polymerase checks the new bases, if there is an incorrect nucleotide, it removes and replaces it, hydrogen bonds form between the pairs (two for A-T and three for C-G) the the DNA winds up into two double helices
• Summary of DNA replication

  A) DNA ligase

  B) RNA primer

  C) DNA polymerase

  D) Primase

  E) DNA polymerase

  F) Parental DNA