What is machinery and enzymes

DNA replication is the basis of biological inheritance where the DNA is copied with the help of various enzymes, such as helicases, topoisomerases, DNA polymerase and DNA ligase. In a bacterial cell, DNA replication begins at a specific point called the ‘origin of replication’. This is the reason why a piece of DNA is cloned into a vector during recombinant DNA procedures, as it is the vector that provides the origin of replication. In eukaryotes with large DNA molecules, there may be many origins of replication that finally merge with one another. During replication, helicases unwind and uncoil the DNA double helix into single strands of DNA by the breakdown of hydrogen bonds. DNA polymerase uses the DNA template to catalyse the polymerisation of deoxyribonucleotides. The deoxyribonucleoside triphosphates act as substrates and also the terminal phosphates in it break down to provide energy as ATP. Due to the high energy requirement, two DNA strands do not always separate completely. But, to facilitate the separation of a DNA helix, the enzyme topoisomerase cuts and rejoins one strand of the DNA, which then unzips the double-stranded DNA. As a result, replication bubbles are formed that extend as a Y-shaped replication fork. This replication fork is actually a small opening in the DNA helix where replication occurs.