Role of Enzymes in DNA Replication

DNA is made up of a double helix of two complementary stands. Different enzymes are involved in various stages of replication, contributing to the unwinding of the DNA double helix, synthesis of new strands, and error correction. Here are some key enzymes and their roles in DNA replication:

DNA Helicase prokaryotes/Eukaryotes

DNA helicase was discovered in E.coli in 1976. It is also called helix destabilize enzyme or unzipping or unwinding enzyme since it separates the two strands of DNA at replication. They are the motor proteins that move directionally along the nucleic acid. It unwind the DNA double helix by breaking the hydrogen bonds between complementary base pairs, creating the replication fork.

DNA Polymerase

DNA polymerases are the enzymes that synthesize the DNA molecules from ribonucleotides, the building blocks of DNA strands. The DNA polymerase reads the existing DNA strand to create the new strands that match the existing one and also performs the proofreading and error correction. The  DNA polymerase catalyzes the  DNA template and directs the extension of the 3′ end of the DNA strand by nucleotide at a time. DNA polymerases can be further divided into two different families which are as follows.

Prokaryotic DNA Polymerase Types and Functions

• DNA Polymerase I is coded by the polA gene. It is a single polypeptide and plays a part in recombination and fixing. It has both 5′????’ and 3′????’ exonuclease action. DNA polymerase ⅰ eliminates the RNA primer from the lagging strand by 5′????’ exonuclease action and furthermore fills the hole.
• DNA Polymerase II is coded by the polB gene. It is comprised of 7 subunits. Its primary job is to repair and furthermore a reinforcement of DNA polymerase III. It has 3′????’ exonuclease action.
•  DNA Polymerase III is the primary enzyme for replication in E.coli. It is coded by polC gene. The polymerization and processivity rate is the most extreme in DNA polymerase III. It additionally has editing 3′????’ exonuclease activity
• DNA Polymerase IV is coded by the dinB gene. Its principal job is in DNA fix during SOS reaction when DNA replication is slowed down at the replication fork. DNA polymerase II, IV and V are translation polymerases.
• DNA Polymerase V is likewise engaged with translation synthesis during SOS reaction and DNA repair.

Eukaryotic DNA Polymerase Types and Functions

• DNA polymerase α – It is the principal protein for replication in eukaryotes. It likewise has 3′????’ exonuclease action for proofreading.
• DNA polymerase γ – The principal capability of DNA polymerase γ is to synthesize primers. The smaller subunit has a primase activity. The biggest subunit has polymerization action. It frames a primer for Okazaki sections, which are then stretched out by DNA polymerase γ.
• DNA polymerase δ – The fundamental capability is DNA repair. It eliminates primers for Okazaki parts from the lagging strand.
• DNA polymerase ε – It is the super replicative enzyme for mitochondrial DNA 

Topoisomerase

Topoisomerase prevents the over-winding of the DNA double helix ahead of the replication fork as the DNA is opening up; it does so by causing temporary nicks in the DNA helix and then resealing it. As synthesis proceeds, the RNA primers are replaced by DNA.

DNA topoisomerases prevent and correct types of topological problems. They do this by binding to DNA and cutting the sugar-phosphate backbone of either one (type I topoisomerases) or both (type II topoisomerases) of the DNA strands. This transient break allows the DNA to be untangled or unwound, and, at the end of these processes, the DNA backbone is resealed. Since the overall chemical composition and connectivity of the DNA do not change, the DNA substrate and product are chemical isomers, differing only in their topology.

DNA Ligase

DNA ligases play an essential role in maintaining genomic integrity by joining breaks in the phosphodiester backbone of DNA that occur during replication and recombination and as a consequence of DNA damage and its repair. Three human genes, LIG1, LIG3 and LIG4 encode ATP-dependent DNA ligases. DNA ligase seals the gaps between Okazaki fragments on the lagging strand by forming phosphodiester bonds. It creates a continuous DNA strand.

Primase

DNA primase is an enzyme whose continual activity is required at the DNA replication fork. They catalyze the synthesis of short RNA molecules used as primers for DNA polymerases. These primers provide starting points for DNA synthesis by DNA polymerase.Primers are synthesized from ribonucleoside triphosphates and are four to fifteen nucleotides long.

Endonucleases

These enzymes catalyze the cleavage of phosphodiester bonds within a DNA or RNA molecule. Unlike exonucleases, which remove nucleotides from the ends of DNA or RNA strands, endonucleases cleave within the molecule itself.

Single-Strand Binding Proteins

These proteins stabilize single-stranded DNA regions, preventing them from re-forming double-stranded structures.

DNA replication is a fundamental biological process by which a cell duplicates its entire DNA. DNA is a self-replicating structure and the replication is catalyzed by enzymes. Through DNA Replication, genetic information is passed on from one generation of cells to the next during cell division. It takes place in the nucleus of eukaryotic cells and the cytoplasm of prokaryotic cells.