Meaning

Function

Structure and Types

Prokaryotic DNA Polymerase

Eukaryotic DNA Polymerase

Mechanism of Action

Arthur Kornberg was the first to purify and characterize a single-chain polypeptide, now known as DNA polymerase-I, from E. coli. Since then, scientists have discovered five DNA polymerases in E. coli that are essential for DNA synthesis.

DNA Polymerase

Definition: A type of enzyme that catalyzes the synthesis of DNA molecules by assembling nucleotides in a specific order.

“DNA polymerases are a group of enzymes that catalyze the synthesis of DNA during replication.” is used for quotes

This statement is being rewritten.

>This statement is being rewritten.

I love to play tennis

I absolutely love to play tennis

DNA polymerases have the primary function of duplicating the DNA content of a cell during cell division. This is accomplished by adding nucleotides to the 3’-OH group of the growing DNA strand.

DNA Polymerase Function

DNA polymerase is an enzyme that is responsible for the replication of DNA. It catalyzes the process of DNA synthesis, which is the process of creating two identical copies of a single strand of DNA from a single original strand. The enzyme works by adding complementary nucleotides to the original strand, forming two new strands that are identical to the original.

Replication

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.

| Check out: NEET 2022 Answer Key PDF|

DNA Polymerase III is the main enzyme responsible for replication in prokaryotes, while in eukaryotes, DNA Polymerase 𝝳 is the main enzyme for replication.

DNA polymerase I removes the RNA primer by its 5’→3’ exonuclease activity and replaces the primer by its polymerase activity in the lagging strand.

Learn more about When does DNA copying occur?.

Fix

The replication process is an immense undertaking and it is essential to preserve the integrity of the genome. In addition to replication errors, DNA repair is a continual process to correct any mistakes in the genome caused by DNA damage. There are a variety of mechanisms by which DNA is repaired.

Proofreading

DNA replication is not perfect and errors occur after every 104 to 105 nucleotides added. To ensure the functionality of proteins and prevent cancer, it is important to remove any incorrect nucleotide sequences or mismatched nucleotides from the newly synthesised strand. DNA polymerases achieve this by utilising 3’→5’ exonuclease activity to move one step back and remove the mismatched pair. This process is known as proofreading.

DNA polymerases are involved in post-replication DNA repair processes and translesion synthesis, in which they copy the unrepaired part of the DNA, thus blocking the progression of replication.

#Let’s Dive Deep into the Different Types of DNA Polymerases and their Functions!

See also: 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.

Types and Function of Prokaryotic DNA Polymerase

All five DNA polymerases identified in E.coli. have distinct structures, functions, rates of polymerization, and processivity.

The polA gene codes for DNA Polymerase I, a single polypeptide involved in recombination and repair. This enzyme has both 5’→3’ and 3’→5’ exonuclease activity. Specifically, its 5’→3’ exonuclease activity is used to remove the RNA primer from the lagging strand, as well as to fill in the gap.

The polB gene codes for DNA Polymerase II, which is composed of 7 subunits. Its primary function is to repair DNA, as well as to act as a backup for DNA Polymerase III. Additionally, it has 3’→5’ exonuclease activity.

DNA Polymerase III, coded by the polC gene, is the main enzyme for replication in E.coli. It has the highest polymerization and processivity rate, as well as a 3’→5’ exonuclease proofreading activity.

The E.coli DNA polymerase III is composed of a total of 13 subunits, consisting of 9 distinct types of subunits.

The two core domains of the DNA polymerase III are composed of 𝜶, 𝟄, and 𝞱 subunits, which are attached to the 𝝲 complex (or clamp-loading complex) that has five subunits: 𝞽2𝝲𝝳𝝳**’**. Moreover, 𝟀 and 𝟁 subunits are also attached to the clamp-loading complex. Finally, two clamps are formed by 𝞫 subunits, with a dimer each, which increases the processivity of the DNA polymerase III.

The dinB gene codes for DNA Polymerase IV, which plays an important role in DNA repair during the SOS response. In this process, DNA Polymerase II, IV and V are translesion polymerases that help to replicate DNA when the replication fork is stalled.

DNA Polymerase V is composed of UmuC monomer and UmuD dimer, and is involved in both translesion synthesis during SOS response and DNA repair.

Types and Functions of Eukaryotic DNA Polymerases

Like prokaryotic cells, eukaryotic cells also have many DNA polymerases, which perform different functions, such as mitochondrial DNA replication and nuclear DNA replication. The nuclear DNA replication is mainly accomplished by DNA polymerase 𝝳 and 𝜶. In human beings, at least 15 DNA polymerases have been identified.

DNA polymerase 𝝳 - It is the main enzyme for replication in eukaryotes and is known for its 3’→5’ exonuclease activity which is used for proofreading.

DNA polymerase 𝜶 - The main function of DNA polymerase 𝜶 is to synthesize primers. The smaller subunit has primase activity, while the largest subunit has polymerization activity. It forms a primer for Okazaki fragments, which is then extended by DNA polymerase 𝝳.

DNA polymerase IV - The main function is DNA repair. It removes primers for Okazaki fragments from the lagging strand.

DNA polymerase δ - It is the main replicative enzyme for mitochondrial DNA.

MCQs on DNA Replication - Check it out!

What is the role of DNA Polymerase?

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

It is important to note that all DNA polymerases require two Mg ions at the active site and can only add nucleotides at the 3′ end of the growing strand, resulting in replication always occurring in the 5’→3’ direction. Additionally, DNA polymerases 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.

The processivity of DNA polymerase determines whether the polymerase will dissociate after adding a nucleotide or continue to add more nucleotides. This processivity differs among different DNA polymerases.

DNA polymerases have two mechanisms to ensure that replication is highly accurate and that there are no mutations due to changes in single nucleotides.

• The geometry of the active sites only allows for the correct nucleotide base pairs to fit, however, this is not enough to guarantee accuracy. It has been observed that after correctly adding 104 to 105 nucleotides, an incorrect nucleotide can still be added.

DNA polymerase has the ability to proofread due to its 3’→5’ exonuclease activity. DNA polymerase I has two active sites - one for polymerizing and one for proofreading - which check each of the added nucleotides and remove any mismatches.

Frequently Asked Questions

I love cats

I love cats

The role of DNA polymerase is to synthesize DNA by assembling nucleotides in the 5’ to 3’ direction.

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 synthesizes the new strand in 5’→3’ direction.

Different DNA polymerases have specific functions. In prokaryotes, DNA polymerase III is the main enzyme for replication, while DNA polymerase I and II are involved in repair, removing the primer and filling the gaps. In eukaryotes, DNA polymerase 𝝳 is the main enzyme for replication, and other DNA polymerases are involved in repair, proofreading and primer removal.

The three main functions of DNA polymerase are:

1. Replication of DNA
2. Repair of damaged DNA
3. Proofreading of newly synthesized DNA strands

The three main functions of DNA polymerase are:

1. Replicate and form new DNA strands
2. Repair any mismatch or damage in the DNA
3. Duplicate the cellular DNA content every time a cell divides so that there is an equal distribution of DNA to the daughter cells

5’→3’ polymerisation - It is required for replication and to add nucleotides at the 3’-OH group of the growing DNA strand, thereby filling the gaps.

3’→5’ exonuclease is required for proofreading and DNA polymerase removes any incorrectly added nucleotides during replication.

5’→3’ exonuclease - It is responsible for removing RNA primers and repairing.

I love going to the beach

I love going to the beach

What are the types of DNA polymerase?

There are several types of DNA polymerase, including DNA polymerase I, DNA polymerase II, DNA polymerase III, DNA polymerase IV, and DNA polymerase V.

Various types of DNA polymerase have been identified in both prokaryotes and eukaryotes.

Prokaryotes contain five different DNA polymerases, labeled I through V.

DNA polymerase III is the main enzyme responsible for replication, while other DNA polymerases are involved in repair, removal of primers, proofreading, and translesion synthesis.

Eukaryotes also contain numerous varieties of DNA polymerase.

DNA polymerase 𝝳 and 𝜶 are the two main DNA polymerases responsible for nuclear replication.

DNA polymerase 𝝲 - It is involved in the replication of mitochondrial DNA.

DNA polymerase IV - 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 is the difference between DNA polymerase and RNA polymerase?

DNA polymerase synthesises DNA during replication and RNA polymerase synthesises RNA during transcription.

Yes, DNA polymerase needs a primer in order to initiate the process of DNA replication.

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 1 and 3 are both enzymes that synthesize DNA. However, DNA polymerase 1 is involved in the repair of damaged DNA, while DNA polymerase 3 is involved in the replication of DNA.

DNA polymerase 3 is the main enzyme responsible for the 5’→3’ polymerisation of DNA strands during replication and also has 3’→5’ exonuclease activity for proofreading. On the other hand, DNA polymerase 1 is the main enzyme for repair, removal of primers and filling the gaps in the lagging strand. Additionally, it has the same polymerisation and 3’→5’ exonuclease activity as DNA polymerase 3, but also has 5’→3’ exonuclease activity.