The ability to reproduce is a fundamental feature of living organisms. Bacteria and fungi have the ability to divide and produce daughter cells which are identical to their parents. Sexually reproducing organisms have progeny that are genetically identical to them. The Enzymes used in Replication are discussed in this article.
DNA Replication
DNA replication is a multistep biological process that produces two identical replicas from a single original DNA molecule. Because it is a crucial aspect of biological inheritance, it can be found in all living species (both prokaryotes and eukaryotes). It necessitates the use of a variety of enzymes, protein components, and metal ions.
Watson and Crick proposed in 1953 that the 2 strands of the DNA would separate & serve as templates for the formation of new complementary strands. Each DNA molecule would contain 1 parental & 1 newly synthesised strand when replication was completed. This demonstrates that DNA replication is a semiconservative procedure.
Enzymes Used in Replication
DNA Helicase
- The helicase enzyme breaks the hydrogen link between 2 strands of the DNA, allowing a single template strand to emerge.
- DNA-B is a major replicative Helicase that attaches to the lagging strand and unwinds the duplex as it moves in a 5′ to 3′ direction.
- Helicase needs ATP as source of energy.
SSB Proteins (Single Stranded Binding Protein)
The SSB protein binds to both single-stranded and double-stranded DNA, preventing the double helix from re-annealing once the helicase unwinds.
The strand separation is maintained by SSB proteins, which also aid in the creation of nascent strand.
Topoisomerase
- DNA A nuclease enzyme called topoisomerase breaks a phosphodiester link in a DNA strand.
- Topoisomerase is a protein that relaxes DNA from its supercoiled state.
- Topoisomerases are enzymes found in every cell that increase (or decrease) the extent of DNA unwinding. The feature of DNA that they affect is the linking number.
There are 2 classes of the Topoisomerase:
- Type – I Topoisomerases
- Type – II Topoisomerases
DNA Primase
- Before the DNA polymerase iii can start building DNA primers, tiny tracts of RNA generated by an enzyme termed as Primases must be present on the template.
- Primase gives an RNA (or DNA) starting point for DNA polymerase to commence synthesis of a new DNA strand.
- Because the free 3′-OH group is required for DNA polymerase to bind to DNA and begin replication.
A phosphodiester bond is formed between the 3′ end of one DNA segment as well as the 5′ end of another by this enzyme. Adjacent Okazaki fragments should be joined together after the RNA primer has been withdrawn and replaced. One fragment’s 3′-OH end is next to the 5′-Phosphate preceding fragment. The enzyme DNA ligase is responsible for securing this nick. Ligases are found in prokaryotes and eukaryotes alike.
DNA Gyrase
DNA Gyrase is a sort of topoisomerase that ensures that the double stranded portions outside of the replication fork do not supercoil.
DNA polymerase
- DNA polymerase enzyme which can synthesise new strand on the DNA template and is DNA dependant.
- Prokaryotes and Eukaryotes have different forms of DNA polymerase.
Conclusion
We can deduce that DNA Replication is a semiconservative process where each of the 2 parental DNA strands serves as a template for the synthesis of new DNA. Each DNA strand has 1 parent strand & 1 daughter strand when DNA replication is complete.
Enzymes used in replication are as follows:
- Helicase
- DNA polymerase
- Primase
- Ligase
- Gyrase
- Topoisomerase