| 1st step of semi conservitave replication | the enzyme DNA helicase breaks the hydrogen bonds between the complementary base pairs of the 2 parental strands of DNA, and the double helix unwinds. this occurs at a number of points, called replication origins, which forms replication forks. Both strands are exposed |
| 2nd step of semi conservitave replication | one strand of the DNA is made by DNA polymerase in a continuous process that occurs in the same direction (5' to 3') as the replication fork is moving. DNA polymerase catalyses the synthesis of leading and lagging strands |
| leading and lagging strands | leading strands is synthesised in the same directon as the replication fork and grows continuously , whereas lagging strand is the opposite, discontinuously by forming short segments called okasaki fragments |
| assembling the lagging strand (3rd stage of replciaton) 1st part | lagging strand runs in 3' to 5' direction, anti parallel. DNA polymerase only works in the 5' to 3' direction. short sections of complementary DNA called the okasaki fragments are made in the 5' to 3' direction |
| assembling the lagging strand (3rd stage of replication) 2nd part | the lagging strands are linked together using DNA ligase to form phosphodiester bonds, ligase only functions on the lagging strands as its the only strand with the okasaki fragments |
| removing wrongly coded DNA | errors: such as an incorrect nucleotide being added to am elongating polynucleotide chain, which causes a mismatch of base pairs.
DNA polymerase checks of mismatch error (DNA proofreading) and repairs them to assemble a new DNA strand |
