DNA replication

• 1 - the original DNA molecule unwinds which is catalysed by DNA gyrase. this enzyme introduces 'negative supercoiling' which untwists the double helix of the DNA.
• 2 - DNA helicase (enzyme) breaks the hydrogen bonds holding the complimentary nucleotide pairs together. the resulting single strands have exposed nucleotide bases.
• 3 - free nucleotides in the nucleoplasm are attracted to complimentary base pairs, forming 2 identical strands. enzyme DNA polymerase catalyses the addition of the new nucleotide bases. the removal of the extra phosphate groups (hydrolysis) supplies the energy to make the phosphodiester bonds between the sugar residues and the phosphate groups of adjoining nucleotides. free phosphorylated nucleotides in the cytoplasm join to their complimentary bases.
• DNA polymerase adds nucleotide bases in the 5' to 3' direction.
• one strand is continually synthesised (leading strand).
• the other strand is synthesised in fragments (lagging strand).
• each fragment of lagging strand is called an Okazaki fragment.
• Okazaki fragments are joined together by another enzyme called ligase.
• mutations are errors when bases pair incorrectly (point mutation) - 1 x 10^8 base pairs.
• enzymes proof read any nucleotides being added.
• slightly different nucleotide sequences produce alleles or different versions of the same gene.
• not all mutations are harmful.