MeaningFunctionStructure and TypesProkaryotic DNA PolymeraseEukaryotic DNA PolymeraseMechanism of Action
DNA polymerases are a group of enzymes required for DNA synthesis. Arthur Kornberg purified and characterized DNA polymerase from E.coli for the first time. It is a single-chain polypeptide now known as DNA polymerase-I. Scientists have now found five DNA polymerases in E. coli.
DNA Polymerase Definition
“DNA Polymerases are a group of enzymes that catalyse the synthesis of DNA during replication.”
The main function of DNA polymerases is to duplicate the DNA content of a cell during cell division. They do so by adding nucleotides at 3’-OH group of the growing DNA strand.
DNA Polymerase Function
The main function of the DNA polymerase is to synthesize DNA by the process of replication. It is an important process to maintain and transfer genetic information from one generation to another. DNA polymerase works in pairs, replicating two strands of DNA in tandem. They add deoxyribonucleotides at the 3′-OH group of the growing DNA strand. The DNA strand grows in 5’→3’ direction by their polymerisation activity. Adenine pairs with thymine and guanine pairs with cytosine. DNA polymerases cannot initiate the replication process and they need a primer to add to the nucleotides.
Also check: NEET 2022 Answer Key PDF
DNA polymerase III is the main enzyme responsible for replication in prokaryotes. In eukaryotes, DNA polymerase 𝝳 is the main enzyme for replication.
DNA polymerase I removes the RNA primer by 5’→3’ exonuclease activity and replaces the primer by its polymerase activity in the lagging strand.
Explore more: When does DNA copying occur?
The replication process is a humongous task and it is important to maintain the integrity of the genome. Apart from replication errors, DNA repair is the continuous process to rectify any errors in the genome due to DNA damage. There are various mechanisms by which DNA is repaired.
DNA replication is not perfect and there occurs an error after every 104 to 105nucleotides added. Removing the incorrect nucleotide sequence or mismatched nucleotides from the newly synthesised strand is very important for the functionality of proteins, which can even lead to cancer. DNA polymerases remove incorrect pairs by exonuclease activity. They move one step back and remove the mismatched pair by 3’→5’ exonuclease activity. This is known as proofreading.
DNA polymerases are also involved in the post-replication DNA repair processes and also in translesion synthesis by which DNA polymerase copies unrepaired part of the DNA blocking the progression of replication.
Let’s learn in detail about different types of DNA polymerases and their functions.
Also see: DNA Ligase
DNA Polymerase Structure and Types
The structure of most of the DNA polymerases resembles a hand, which is holding active sites. The active site of the enzyme has two parts. At the insertion site, nucleotides are added. After adding, the newly formed base-pair migrates to the post-insertion site.
Prokaryotic DNA Polymerase Types and Function
There are five DNA polymerases identified in E.coli. All the DNA polymerases differ in structure, functions and rate of polymerization and processivity.
DNA Polymerase I is coded by polA gene. It is a single polypeptide and has a role in recombination and repair. It has both 5’→3’ and 3’→5’ exonuclease activity.DNA polymerase Ⅰ removes the RNA primer from lagging strand by 5’→3’ exonuclease activity and also fills the gap.
DNA Polymerase II is coded by polB gene. It is made up of 7 subunits. Its main role is in repair and also a backup of DNA polymerase III. It has 3’→5’ exonuclease activity.
DNA Polymerase III is the main enzyme for replication in E.coli. It is coded by polC gene. The polymerization and processivity rate is maximum in DNA polymerase III. It also has proofreading 3’→5’ exonuclease activity.
DNA polymerase III of E.coli is made up of a total of 13 subunits, which comprises 9 different types of subunits.
- It consists of two core domains made up of 𝜶, 𝟄, and 𝞱 subunits. It is attached to the 𝝲 complex or clamp-loading complex, which is made up of five subunits, 𝞽2𝝲𝝳𝝳’. Additional subunits 𝟀 and 𝟁 are attached to the clamp-loading complex. 𝞫 subunits make two clamps with a dimer each. They increase the processivity of the DNA polymerase III.
DNA Polymerase IV is coded by dinB gene. Its main role is in DNA repair during SOS response, when DNA replication is stalled at the replication fork. DNA polymerase II, IV and V are translesion polymerases.
DNA Polymerase V is also involved in translesion synthesis during SOS response and DNA repair. It is made up of UmuC monomer and UmuD dimer.
Eukaryotic DNA Polymerase Types and Function
Like prokaryotic cells, eukaryotic cells also have many DNA polymerases, which perform different functions, e.g. mitochondrial DNA replication, nuclear DNA replication, etc. The nuclear DNA replication is mainly done by DNA polymerase 𝝳 and 𝜶. There are at least 15 DNA polymerases identified in human beings.
- DNA polymerase 𝝳 – It is the main enzyme for replication in eukaryotes. It also has 3’→5’ exonuclease activity for proofreading.
- DNA polymerase 𝜶 – The main function of DNA polymerase 𝜶 is to synthesize primers. The smaller subunit has a primase activity. The largest subunit has polymerization activity. It forms a primer for Okazaki fragments, which is then extended by DNA polymerase 𝝳.
- DNA polymerase 𝟄 – The main function is DNA repair. It removes primers for Okazaki fragments from the lagging strand.
- DNA polymerase 𝝲 – It is the main replicative enzyme for mitochondrial DNA.
Also Check: MCQs on DNA Replication
How does DNA Polymerase work?
The reaction is phosphoryl group transfer. The 3’-OH group of the growing strand acts as a nucleophile and attacks the incoming deoxyribonucleoside triphosphate at the 𝜶-phosphorus, leading to phosphodiester bond formation. Inorganic phosphate is released in the reaction.
(dNMP)n + dNTP → (dNMP)n+1 + PPi
All the DNA polymerases require two Mg ions at the active site. It is important to note that DNA polymerase can only add nucleotides at the 3′ end of the growing strand, that is why replication always occurs in the 5’→3’ direction. They cannot initiate the formation of new DNA.
They need a template strand, which guides the polymerisation reaction. They also need a primer for their action as they can only add nucleotides at 3’ OH group. The primer can be a short segment of RNA, DNA or both. Generally, the primer is an RNA oligonucleotide in the living system.
After adding a nucleotide, the DNA polymerase can either dissociate or move along to add more nucleotides. It depends on the processivity of DNA polymerase and it differs in different DNA polymerases.
Replication is a highly accurate process and even the change in a single nucleotide can cause mutation. To avoid this there are two mechanisms by which DNA polymerases ensure that there are no discrepancies.
- The geometry of the active sites allows only the correct nucleotide base pairs to fit. But this is not sufficient and it is seen that it can add an incorrect nucleotide after correctly adding 104 to 105 nucleotides.
- To correct this type of errors, DNA polymerase has 3’→5’ exonuclease activity. DNA polymerase checks each of the added nucleotides and removes the nucleotide if there is a mismatch. This is known as proofreading. In DNA polymerase I, there are different active sites for polymerizing and proofreading functions.
This was all about DNA Polymerase. Explore notes on Molecular Basis of Inheritance to know in detail about the replication process, only at BYJU’S.
Frequently Asked Questions
What is the role of DNA polymerase?
The main function of DNA polymerase is to synthesize DNA by the process of replication. It adds deoxyribonucleotides at the 3′-OH group of the growing DNA strand and synthesises the new strand in 5’→3’ direction.
Also see: Nucleotide
Different DNA polymerases perform specific functions. In prokaryotes, DNA polymerase III is the main enzyme responsible for replication. DNA polymerase I and II have a role to play in repair, removing the primer and filling the gaps. In eukaryotes, DNA polymerase 𝝳 is the main enzyme for replication. Other DNA polymerases are involved in the repair, proofreading and primer removal.
What are the 3 main functions of DNA polymerase?
The main function of DNA polymerase is to replicate and form new DNA strands and repair any mismatch or damage in the DNA. DNA polymerase duplicates the cellular DNA content every time a cell divides so that there is an equal distribution of DNA to the daughter cells. The three main functions of DNA polymerase are:
- 5’→3’ polymerisation – it is required for replication and to add nucleotides at the 3’-OH group of the growing DNA strand and filling the gaps.
- 3’→5’ exonuclease – it is required for proofreading and DNA polymerase removes any incorrectly added nucleotides while replication.
- 5’→3’ exonuclease – It is responsible for removing RNA primers and repair.
What are the types of DNA polymerase?
There are various different types of DNA polymerase identified in prokaryotes and eukaryotes:
- Prokaryotes contain five different DNA polymerases named from I to V.
DNA polymerase III – is the main enzyme responsible for replication. Other DNA polymerases take part in repair, removing, primer, proofreading, translesion synthesis.
- Eukaryotes also contain many different types of DNA polymerase.
DNA polymerase 𝝳 and 𝜶 – The main DNA polymerases for nuclear replication.
DNA polymerase 𝝲 – It is involved in mitochondrial DNA replication.
DNA polymerase 𝟄 – Its main function is to repair DNA. It removes primer from Okazaki fragments.
Which DNA polymerase is used in DNA replication?
DNA polymerase III is used in the replication process in prokaryotic cells and DNA polymerase 𝝳 is the main enzyme for replication in eukaryotic cells.
What’s the difference between DNA polymerase and RNA polymerase?
DNA polymerase synthesises DNA during replication and RNA polymerase synthesises RNA during transcription.
Does DNA polymerase need a primer?
Yes, DNA polymerase requires a primer as they can add a nucleotide to the 3’-OH group of a DNA strand. DNA polymerases cannot initiate the replication process and they need a primer to add nucleotides.
What is the difference between DNA polymerase 1 and 3?
DNA polymerase 3 is the main enzyme catalysing the 5’→3’ polymerisation of DNA strand during replication. It also has 3’→5’ exonuclease activity for proofreading. Whereas DNA polymerase 1 is the main enzyme for repair, removal of primers and filling the gaps in the lagging strand. Apart from polymerisation and 3’→5’ exonuclease activity like DNA polymerase 3, it also has 5’→3’ exonuclease activity.
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What is the structure and function of DNA polymerase? ›
DNA polymerase (pol) β is a small eukaryotic DNA polymerase composed of two domains. Each domain contributes an enzymatic activity (DNA synthesis and deoxyribose phosphate lyase) during the repair of simple base lesions. These domains are termed the polymerase and lyase domains, respectively.What is DNA polymerases and its types? ›
Classification. On the basis of sequence similarities, DNA polymerases can fall into three groups: type A, type B and type C, which have homology to polA (pol I), polB (pol II) and polC (pol III) from Escherichia coli, respectively [1,2].What is the structure of DNA polymerases? ›
DNA polymerases are molecular motors directing the synthesis of DNA from nucleotides. All polymerases have a common architectural framework consisting of three canonical subdomains termed the fingers, palm, and thumb subdomains.What are the main functions of DNA polymerase group of answer choices? ›
- Replication: The DNA polymerase enzymes double the amount of DNA in a cell during cell division.
- Proofreading: The DNA polymerase enzymes also proofread the duplicated DNA and repair it.
Primary functions of DNA polymerases. DNA polymerases are a group of polymerases that catalyze the synthesis of polydeoxyribonucleotides from mono-deoxyribonucleoside triphosphates (dNTPs), performing the most fundamental functions in vivo of DNA replication, repair, and, in some cases, cell differentiation.What are the functions of DNA polymerase quizlet? ›
The DNA polymerase is the enzyme that joins individual nucleotides to produce a new strand of DNA it produces the sugar phosphate bonds that join the nucleotides together and it proof reads each new DNA strand so that each copy is a near perfect copy of the original.What are the 3 types of polymerases? ›
Abstract. All eukaryotes have three different RNA polymerases (RNAPs) which transcribe different types of genes. RNA polymerase I transcribes rRNA genes, RNA polymerase II transcribes mRNA, miRNA, snRNA, and snoRNA genes, and RNA polymerase III transcribes tRNA and 5S rRNA genes.What are the 5 types of polymerase? ›
The eukaryotic cell contains five DNA polymerase α, β, γ, δ, and ε. Polymerase γ is found in the cell mitochondria and it actively replicates the mitochondrial DNA, while polymerase α, β, δ are found in the cell nucleus hence are involved in the nuclear DNA replication.How many types of polymerase are there? ›
|Family||Types of DNA polymerase||Examples|
|C||Replicative Polymerases||Pol III|
|D||Replicative Polymerases||PolD (DP1/DP2 heterodimer)|
|X||Replicative and Repair Polymerases||Pol β, Pol σ, Pol λ, Pol μ, and terminal deoxynucleotidyl transferase|
|Y||Replicative and Repair Polymerases||Pol ι, Pol κ, Pol η, Pol IV, and Pol V|
DNA polymerase I is a single polypeptide chain with 928 amino acids and molecular weight of 109 kDa. It has three sites, which provide three distinct catalytic activities: 3′ to 5′ exonuclease, 5′ to 3′ exonuclease, and 5′ to 3′ polymerase.
What is the structure of DNA polymerase III? ›
DNA polymerase III is a holoenzyme, which has two core enzymes (Pol III), each consisting of three subunits (α, ɛ and θ), a sliding clamp that has two beta subunits, and a clamp-loading complex which has multiple subunits (δ, τ, γ, ψ, and χ).What is the structure and function of DNA polymerase in prokaryotes? ›
The core comprises three subunits – the α subunit which is the polymerase activity hub, the δ subunit which is the exonucleolytic proofreader, and the θ subunit which may stabilize δ. The core and the beta sliding clamp are present in duplicate, to allow for processing of both the leading and lagging DNA strands.What are the main functions of DNA polymerase Quizizz? ›
DNA polymerase synthesizes a complementary strand from each of the original strands. DNA ligase breaks apart one of the original strands, and other enzymes re-assemble the components into a new strand.What are the functions of DNA polymerase I and III? ›
|DNA Pol I||Remove the RNA primer and replace it with a matching DNA sequence|
|DNA Pol II||Responsible for healing damage to the DNA strand|
|DNA Pol III||Primary DNA polymerase responsible for synthesizing new DNA during replication|
A polymerase is an enzyme (EC 2.7. 7.6/7/19/48/49) that synthesizes long chains of polymers or nucleic acids. DNA polymerase and RNA polymerase are used to assemble DNA and RNA molecules, respectively, by copying a DNA template strand using base-pairing interactions or RNA by half ladder replication.What is the function of DNA polymerase 3 quizlet? ›
DNA polymerase III adds DNA nucleotides to the primer(s), synthesizing the DNA of both the leading and the lagging strands.What are the three different roles of DNA polymerase quizlet? ›
- Adds DNA nucleotides to the end of the RNA primer.
- Catalyses the formation of a new strand of DNA, matching the old one.
- Proofreads its work to double-check that it didn't make any mistakes. If it did, it then makes a new, correct, nitrogen base pair and fixes the problem.
DNA polymerase - An enzyme that assembles new DNA by copying an existing strand. DNA is double stranded and uses Thymine as a base. RNA polymerase - an enzyme that synthesizes the formation of RNA from a DNA template during transcription.What are the two roles of DNA polymerase in replication? ›
They provide polymerase activity under two broad categories; normal replication and repair. Under conditions of normal replication, DNA polymerase corrects errors by 3′ → 5′ exonuclease activity.How many DNA polymerases are there? ›
Cells contain at least 13 documented DNA polymerases that might have different functions. The five earliest-identified DNA polymerases (α, β, δ, ε and γ) are essential proteins that have key roles in nuclear DNA- or mitochondrial DNA-mediated transactions.
How many DNA polymerases are in a cell? ›
Eukaryotic cells contain five DNA polymerases: α, β, γ, δ, and ε. Polymerase γ is located in mitochondria and is responsible for replication of mitochondrial DNA.What are the three domains of DNA polymerase? ›
The polymerase domain includes the C-subdomain (catalytic), the D-subdomain (DNA binding), and the N-subdomain (nascent base pair binding) that are equivalent to the palm, thumb, and fingers subdomains, respectively, of right-handed DNA polymerases (Figure 2).What type of polymerase is DNA polymerase? ›
DNA polymerase (DNAP) is a type of enzyme that is responsible for forming new copies of DNA, in the form of nucleic acid molecules. Nucleic acids are polymers, which are large molecules made up of smaller, repeating units that are chemically connected to one another.What is the function of DNA polymerase 5? ›
DNA Polymerase V (Pol V) is a polymerase enzyme involved in DNA repair mechanisms in bacteria, such as Escherichia coli. It is composed of a UmuD' homodimer and a UmuC monomer, forming the UmuD'2C protein complex.What is DNA polymerase summary? ›
DNA polymerase is a specific class of enzyme found in all living organisms. Its main purpose is to replicate DNA and to help in the repair and maintenance of DNA. The enzyme is critical to the transmission of genetic information from generation to generation.What are the properties of DNA polymerase? ›
Each thermostable DNA polymerase has its own set of unique characteristics, including thermostability, extension rate, fidelity, processivity, specificity, resistance to contaminants and inhibitors, modified nucleotide selection, ability to bypass damage, nuclease activity, and strand displacement activity.What is the difference between polymerase 1/2 and 3? ›
RNA Polymerase I is an enzyme that transcribes ribosomal RNAs. RNA Polymerase II is an enzyme that transcribes precursors of mRNAs. RNA Polymerase III is an enzyme that transcribes tRNAs. It transcribes all rRNAs except the 5S rRNA component.What is the function of DNA polymerase first? ›
DNA polymerase I of eubacteria functions in vivo to synthesize short stretches of DNA during excision repair and to remove RNA primers and fill the gaps between Okazaki fragments in lagging strand replication.What is DNA polymerase 1 vs 2 vs 3? ›
The key difference between DNA polymerase 1 2 and 3 mainly relies on the prime function of each enzyme. DNA polymerase 3 is the main enzyme which catalyzes the DNA synthesis, while DNA polymerase 1 and 2 are involved in DNA repairing and proofreading.What is polymerase III made of? ›
The DNA polymerase III holoenzyme is composed of 10 subunits. The core of the polymerase contains the catalytic polymerase subunit, alpha, the proofreading 3'-->5' exonuclease, epsilon, and a subunit of unknown function, theta.
What is the function of DNA polymerase in eukaryotes? ›
A major function of DNA polymerases is to accurately replicate the six billion nucleotides that constitute the human genome. This task is complicated by the fact that the genome is constantly challenged by a variety of endogenous and exogenous DNA-damaging agents.What is the function of DNA polymerase alpha in eukaryotes? ›
DNA polymerase alpha (pol alpha) holds a special position among the growing family of eukaryotic DNA polymerases. In fact, pol alpha is associated with DNA primase to form a four subunit complex and, as a consequence, is the only enzyme able to start DNA synthesis de novo.What are the different types of DNA polymerases in prokaryotes? ›
In prokaryotes, three main types of polymerases are known: DNA pol I, DNA pol II, and DNA pol III. DNA pol III is the enzyme required for DNA synthesis; DNA pol I and DNA pol II are primarily required for repair. There are specific nucleotide sequences called origins of replication where replication begins.What is the main DNA polymerase? ›
DNA polymerases are enzymes that create DNA molecules by assembling nucleotides, the building blocks of DNA. These enzymes are essential to DNA replication and usually work in pairs to create two identical DNA strands from one original DNA molecule.What are the 4 types of polymerase? ›
Polymerase α, Polymerase δ, and Polymerase ε
Members of family B, Pol α, Pol δ, and Pol ε are the main polymerases involved in DNA replication. Pol α binds with primase to form a complex. Primase creates and places an RNA primer, allowing Pol α to start replication.
Eukaryotic cells contain five DNA polymerases: α, β, γ, δ, and ε. Polymerase γ is located in mitochondria and is responsible for replication of mitochondrial DNA. The other four enzymes are located in the nucleus and are therefore candidates for involvement in nuclear DNA replication.What are the functions of DNA polymerase III and III? ›
In prokaryotes, DNA polymerase III is the main enzyme responsible for replication. DNA polymerase I and II have a role to play in repair, removing the primer and filling the gaps. In eukaryotes, DNA polymerase 𝝳 is the main enzyme for replication.What is the function of DNA polymerase 2? ›
DNA Polymerase II is a member of the polymerase B family and supports Polymerase III in DNA replication moving from the 3′ end to the 5′ end. In the case when Polymerase III stalls during a replication error, Polymerase II can interrupt and excise the mismatched bases.What is the difference between DNA polymerase 1 2 and 3? ›
The key difference between DNA polymerase 1 2 and 3 mainly relies on the prime function of each enzyme. DNA polymerase 3 is the main enzyme which catalyzes the DNA synthesis, while DNA polymerase 1 and 2 are involved in DNA repairing and proofreading.How many structural classes are in DNA polymerase? ›
The eukaryotic cell contains five DNA polymerase α, β, γ, δ, and ε. Polymerase γ is found in the cell mitochondria and it actively replicates the mitochondrial DNA, while polymerase α, β, δ are found in the cell nucleus hence are involved in the nuclear DNA replication.