DNA Replication Enzymes

Eukaryotic and prokaryotic cells contain several types of DNA replication enzymes.

Both eukaryotes and prokaryotes contain different types of DNA replication enzymes and they play an important role in the process of DNA replication.

Prokaryotic DNA Replication Enzymes:

  • DNA polymerase I
  • DNA polymerase II
  • DNA polymerase III
  • helicase
  • Single Stranded Binding (SSB) Protein
  • primase
  • sliding clamp
  • ligase

DNA polymerase I:

DNA polymerase I has exonuclease activity to remove RNA primers. These gaps are filled by DNA molecules. This enzyme is unique among prokaryotes and is encoded by the polA gene.

DNA polymerase II:

This enzyme repairs DNA molecules. This enzyme gene is encoded by the polB gene.

DNA polymerase III:

It has polymerase activity and attaches nucleotides to newly synthesized bases in the 5′ to 3′ directions.

It has three main parts. They are the Pol III core, the Beta sliding clamp and the clamp-loading complex.


This unwinds the DNA and unwinds the strands to form the replication fork.

Single Stranded Binding (SSB) Proteins:

These proteins bind to the DNA molecule and prevent the conformation of the DNA double helix structure by not allowing the formation of hydrogen bonds between nucleotides.


It synthesizes RNA primers that are needed in the replication process.

Sliding Clamp:

It surrounds the DNA molecule by forming a ring around it. It helps the DNA polymerase to bind to the template strand at the time of new strand synthesis.


This enzyme binds together Okazaki fragments that are formed in lagging strand synthesis to form a DNA strand.

DNA Replication Enzymes
DNA Replication Enzymes

Eukaryotic DNA Replication Enzymes:

  • helicase
  • DNA polymerase (α, β, , and ).
  • telomerase
  • DNA Topoisomerase I
  • DNA topoisomerase II
  • DNA ligase

DNA polymerase (α, β, , and ) :

Eukaryotes have five types of DNA polymerases.

  1. DNA replication is aided by the DNA polymerase α and .
  2. DNA repair is aided by the DNA polymerase β and .
  3. Mitochondrial DNA is replicated by DNA polymerase.
  4. DNA polymerase also synthesizes RNA primers.
  5. The lagging strand is synthesized by the DNA polymerase α and .
  6. The leading strand is synthesized by DNA polymerase.


This enzyme plays an important role in the synthesis of telomeres that have a repeating sequence at both ends. These help to prevent the fusion of nearby chromosomes.

DNA Topoisomerase I:

It is the most important enzyme in DNA replication.

This cuts one of the two strands of DNA and relaxes the double helix formation.

It assists in the creation of replication forks.

DNA Topoisomerase II:

It prevents the supercoiling of DNA during the replication process.

It can cut both strands and create nicks in the DNA strand.

DNA ligase:

This enzyme joins the two ends by forming a 3′-5′ phosphodiester bond.

Bacterial DNA Replication Enzymes:

  • DNA polymerase I
  • DNA polymerase II
  • DNA polymerase III
  • helicase
  • DNA gyres
  • ligase
  • primase

These enzymes are discussed in detail in Prokaryotic DNA Replication Enzymes.

Function of DNA Replication Enzymes:

DNA polymerIt has the ability to synthesize new threads. It can also act as an exonuclease activity to remove PRIMERs. It can proof read DNA coding and correct DNA.  
DNA HelicaseIt forms a replication fork by forming a nick in the DNA double helix structure.
topoisomeraseIt can prevent supercoiling of DNA during replication.
DNA primase    It synthesizes RNA primers that are important in the initiation of DNA replication.
 DNA ligase These enzymes bind to the Okazaki fragments of the lagging strand and form the DNA strand. It also connects the two ends of the circular DAN after the completion of replication in prokaryotes. It connects or ends fragments by forming 3′-5′ phosphodiester bonds.

questions to ask:

What is meant by DNA?

DNA is the genetic material that is present in chromosomes.

Deoxyribonucleic acid is a part of chromosomes and it transfers heredity traits from one generation to another.

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:

A-form DNA is right-handed in nature and is composed of deoxyribonucleic acid and this form of DNA is sometimes found in cells.

In this form the two are parallel in nature.


This form of DNA resembles the double helix structure and is the most abundant form of DNA in cells.

It is first proposed by Watson and Francis Crick. He postulated that the two DNA strands are held together to form a double helix structure by hydrogen bonds and wound in the same spindle.


It is a left-handed double helix structure in a zig-zag pattern.