There are several types of DNA replicative enzymes are in eukaryotic and prokaryotic cells.
Both eukaryotes and prokaryotes have various types of DNA replicative enzymes and they plays a vital role in the process of DNA replication.
Prokaryotic DNA Replication Enzymes:
DNA Polymerase I:
DNA polymerase I has the exonuclease activity to remove RNA primers. These gaps are filled by DNA molecules. This enzyme is unique among prokaryotes and is encoded by PolA gene.
DNA Polymerase II:
This enzyme repairs the DNA molecules. This enzyme is encoded by the gene PolB gene.
DNA Polymerase III:
It has the polymerase activity and adds nucleotides to the newly synthesised bases in 5’ to 3’ directions.
It has three main parts. Those are pol III core, the beta sliding clamp and clamp- loading complex.
It unwinds the DNA and opens the strands to form replication forks.
Single stranded binding (SSB) proteins:
These proteins attach to the DNA molecule and averts the reforming of DNA double helix structure by not allowing the formation of hydrogen bonds between nucleotides.
It synthesises the RNA primers which are needed in replication process.
This encloses the DNA molecule by forming a ring around it. This helps in the binding of DNA polymerase to the template strand at the time of new strand synthesis.
This enzyme binds the okazaki fragments together which are formed in lagging strand synthesis to form a DNA strands.
Eukaryotic DNA Replication Enzymes:
DNA polymerase (α, β, γ, δ and ε):
There are five types of DNA polymerases in eukaryotes.
- The DNA replication is aided by the DNA polymerase α and δ.
- The repair of DNA is aided by the DNA polymerase β and ε.
- The mitochondrial DNA is replicated by DNA polymerase γ.
- The DNA polymerase also synthesizes the RNA primers.
- The lagging strand is synthesized by the DNA polymerase α and δ.
- The leading strand is synthesized by the DNA polymerase δ.
This enzyme plays a key role in the synthesis of telomers which have repetitive sequence at both the ends. These help in the prevention of fusion of nearby chromosomes.
DNA Topoisomerase I:
This is the most important enzyme in DNA replication.
It makes a cut in one of the two strands of DNA and relaxes the double helix formation.
This aids in the formation of replication fork.
DNA Topoisomerase II:
It prevents the supercoiling of DNA during replication process.
It can make cut in both the strands and forms nick in DNA strand.
This enzymes joins both the ends by forming a 3’-5’ phosphodiester bond.
Bacterial DNA Replication Enzymes:
These enzymes are discussed in prokaryotic DNA replication enzymes in detail.
Function of DNA Replication Enzymes:
|DNA polymerase||It has the ability of synthesizing new strands. It can also act as an exonuclease activity to remove PRIMERS. It can proof read the DNA coding and corrects the DNA.|
|DNA Helicase||It forms the replication fork by making a nick in the DNA double helix structure.|
|topoisomeraseIt can prevent the super coiling of DNA while replication.|
|DNA primase||It synthesises the RNA primers which important in the initiation of replication of DNA.|
|DNA ligase This enzymes joins the okazaki fragments of lagging strand and forms the DNA strands. This also joins the two ends of circular DAN after completion of replication in prokaryotes. It joins the fragments or ends by forming the 3’-5’ phosphodiester bond.|
Read More On: Bacterial DNA Replication Steps.
Frequently Asked Questions:
What is meant by DNA?
DNA is the genetic material which presents in chromosomes.
Deoxyribonucleic acid is a part of chromosomes and it transfers the heredity characters from one generation to another generation.
How many types of DNA are there and what are they?
In general there are three types of DNA present in chromosomes.
They are A-form, B-form, Z-form.
A-form DNA is right handed in nature and it is composed of deoxyribonucleic acids and this form of DNA is occasionally found in cells.
In this form the two are antiparallel in nature.
This form of DNA is looks like double helix structure and this is the most abundant form of DNA in cells.
This is first proposed by Watson and Francis Crick. They said that two DNA strands are held together by the hydrogen bonds and wound in the same axis to form a double helix structure.
It is left handed double helix structure in a zig-zag pattern.