1. 1. DNA polymerase is an essential component for PCR due to its key role in synthesizing new DNA strands. After proofreading, the overall error rate of nucleotide incorporation is approximately 1 in 107. Missed the LibreFest? Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. In E. coli, the OriC origin is ~245 bp in size. This is the main replicating enzymes in prokaryotes which is mainly responsible for the synthesis of new DNA strands (5′ to 3′ polymerase … See the whole complex in action in this animation: The ends of linear chromosomes present a problem – at each end one strand cannot be completely replicated because there is no primer to extend. The resulting DNA fragments are then "sealed" together with DNA ligase. Pol III begins synthesizing by adding nucleotides onto the 3’ end of a primer and continues until it hits the 5’ end of the next primer. In this interview, News-Medical speaks to Dr. Howard Hu about his latest research into cadmium and how it could be causing more severe pneumonia infections. "Prokaryotic DNA Polymerases". And DNA polymerase I it is responsible for removing RNA primers and replacing them with DNA. The difference between DNA Polymerase 1 and 3 is that DNA Polymerase 1 is vital to replicate the DNA. Another antibiotic known as streptolydigin inhibits the elongation process of bacterial RNA polymerization… Endonucleases 5. Unlike Pol III, Pol I is a monomeric protein and acts alone, without additional proteins. Pol I accounts for more than 95% of polymerase activity in E. coli, although cells that lack this polymerase have been found and its activity can be replaced by the other four types of polymerase. DNA polymerase I and II have a role to play in repair, removing the primer and filling the gaps. Polymerase II is a DNA repair enzyme with a 3’ to 5’ exonuclease activity. The enzyme aids the base pairing of incoming nucleotides with the template strand. DNA polymerases in Prokaryotes DNA polymerase I This is a repair polymerase and is involved in excision repair with 3'-5' and 5'-3' exonuclease activity and processing of Okazaki fragments generated during lagging strand synthesis. Prokaryotic cells have multiple origins of replication. In starting it was believed that it is a replication enzyme, but after further study, it was evidenced that it is more a DNA repair enzyme rather than a replication enzyme. Polynucleotide Ligase 4. This happens in cancer cells, which can form tumors as well as in cells in culture, such as HeLa cells, which can be propagated essentially indefinitely. Prokaryotic DNA Polymerases. DNA polymerases in prokaryotes and eukaryotes: mode of action and biological implications. 5’-3’ polym… In prokaryotes polycistronic transcript are commonly present like one promotor is sufficient For genes. Legal. The enzyme is expressed by a gene (dinB) that is switched on when polymerases stall at the replication fork. How will the 3' end be replicated when there is no longer a place for a primer on the complementary strand? News-Medical, viewed 26 December 2020, https://www.news-medical.net/life-sciences/Prokaryotic-DNA-Polymerases.aspx. Pol I accounts for more than 95% of polymerase activity in E. coli, although cells that lack this polymerase have been found and its activity can be replaced by the other four types of polymerase. DNA is synthesized by DNA polymerases. Occurs as linear DNA with two ends. DNA polymerase 3 is the main enzyme involved in prokaryotic DNA replication. Once oriC has been opened and the helicases have attached to the two sides of the replication fork, the replication machine, aka the replisome can begin to form. DNA polymerase III is a multi-subunit holoenzyme, with α, ε, and θ subunits comprising the core polymerase, and τ, γ, δ, δ’, χ, Ψ, … Four of these subunits, denoted α, α, β, and β′ comprise the polymerase core enzyme. Replication occurs in the nucleus. DNA polymerases in Prokaryotes DNA polymerase I This is a repair polymerase and is involved in excision repair with 3'-5' and 5'-3' exonuclease activity and processing of Okazaki fragments generated during lagging strand synthesis. DNA polymerase I replaces the RNA primer with DNA. Why would an initiator binding site in the OriC be an AT-rich region? In eukaryotes, 5 different DNA polymerase are at work. DNA polymerase can only extend in the 5′ to 3′ direction, which poses a slight problem at the replication fork. It was discovered by Thomas Kornberg in 1970. The dissociation of σ allows the core enzyme to proceed along the DNA template, synthesizing mRNA in the 5′ to 3′ direction at a rate of approximately 40 nucleotides per second. Please use one of the following formats to cite this article in your essay, paper or report: Mandal, Ananya. DNA Polymerase I It is the first DNA polymerase to be isolated and purified. Occur inside the nucleus (some in mitochondria and some in chloroplasts). This 5’-3’ exonuclease then removes the RNA primer. DNA polymerase has two important restrictions: it is able to add nucleotides only in the 5′ to 3′ direction (a new DNA strand can be only extended in this direction). Why are some groups more vulnerable to COVID-19? 3. The 5’-3’ exonuclease activity is crucial in removing the RNA primer. The primary DNA polymerase for replication in E. coli is DNA Polymerase III (Pol III). 2. Another DNA polymerase isolated from Theimus aquaticus has been described (Chien et al., 1976; Kaledin et al., 1980).This enzyme has an approximate molecular weight of 62,000–68,000, a specific activity between 500 and 5200 U/mg, a temperature optimum of 70–80 ° C, and a pH optimum in the range of 7.8 to 8.3 (see Table 2).Optimal activity is obtained with 60–200 mM KCl and 10 mM Mg 2 +. Consequently, understanding the characteristics of this enzyme and the subsequent development of advanced DNA polymerases is critical for adapting the power of PCR for a … Being the primary holoenzyme involved in replication activity, the DNA Pol III holoenzymeal… There are different forms of DNA polymerase enzyme found in eukaryotes and prokaryotes. DNA po… It is important to mention that DNA replication in both prokaryotes and eukaryotes is bidirectional i.e., 5’ — > 3’ direction. Enzyme # 1. Furthermore, they are the enzymes responsible for transcription in which genetic information in genes is copied to RNA molecules. Helicase 7. The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical. It attached the deoxyribo nucleotide to the 3’-OH group of RNA/DNA primer. The DNA content of the parent is doubled by means of replication mechanism aided by a specific enzyme, DNA polymerases. DNA replication is called a semi-discontinuous process because while the leading strand is being synthesized continuously, the lagging strand is synthesized in fragments. DNA polymerase 1, 2 and 3 are found only in prokaryotic organisms, and they play different roles in DNA replication. It also requires a free 3′-OH group to which it can add nucleotides by forming a phosphodiester bond between the 3′-OH end and the 5′ phosphate of the next nucleotide. DNA Polymerase 2. In fact, the pol III complexes are physically linked through τ subunits. DNA polymerase has two important restrictions: it is able to add nucleotides only in the 5′ to 3′ direction (a new DNA strand can be only extended in this direction). The process in which genetic material is transferred from DNA to RNA is called transcription.in this process DNA strand is used as a template and mRNA is synthesized. DNA polymerase I has 5’- 3’ exonuclease activity. The helicase will continue to travel in front of the fork to unwind new DNA and allow primase to add new primers as needed. However, DNA polymerase cannot begin the formation of this new chain on its own and can only add nucleotides to a pre-existing 3′-OH group. A number of possibilities have been proposed, but the current model is depicted here. Recall that enzymes are specific to their substrates. A. DNA synthesis always occurs from 5’ to 3’ direction. We use cookies to enhance your experience. […] 4. Recall that sister chromatids are identical copies of each other produced during S phase. It also requires a free 3′-OH group to which it can add nucleotides by forming a phosphodiester bond between the 3′-OH end and the 5′ phosphate of the next nucleotide. Form chromosome or chromatin in the nucleus. The overall direction of the lagging strand will be 3' to 5', and that of the leading strand 5' to 3'. In addition, prokaryotes often have abundant plasmids, which are shorter circular DNA molecules that may only contain one or a few g… Both DNA polymerase 1 and 3 possess replicative activity in the 5’ to 3’ direction. The overall process of DNA replication is similar in all organisms. This DNA polymerase has a poor processivity rate, adding around 15 to 20 nucleotides per second. Although only a few nucleotides are needed, the prokaryotic primers may be as long as 60 nt depending on the species. Thereby, it is preventing the enzyme from initiating bacterial RNA polymerization. She specialized in Clinical Pharmacology after her bachelor's (MBBS). News-Medical. Similarities Between Prokaryotic and Eukaryotic RNA Polymerase . Explain how telomerase replicates ends of chromosomes and the cellular significance of chromosome shortening, addressing the specific function of telomerase RNA. Telomerases are RNA-directed DNA polymerases. DNA replicationis essential to organisms, and a great deal of effort has been devoted to understanding its mechanism. How can one complex make new DNA in opposite directions? DNA polymerase is able to add nucleotides only in the 5' to 3' direction (a new DNA strand can be only extended in this direction). The prokaryotes, which include bacteria and archaea, are mostly single-celled organisms that, by definition, lack membrane-bound nuclei and other organelles. In … DNA polymerase take part in the process of replication while during transcription RNA polymerase plays its role. They are a riboprotein, as they are composed of both protein and RNA. Mandal, Ananya. Taq DNA polymerase is one of a DNA polymerase enzyme which is highly useful in polymerase chain reaction (PCR) method of DNA amplification. DNA polymerase 1 and 3 are two types of DNA polymerases involved in prokaryotic DNA replication.DNA polymerases assist the synthesis of a new DNA strand by assembling the nucleotides to the parent strand. ; Its main function is excision repair of DNA strands from the 3′-5′ direction to the 5′-3 direction, as an exonuclease. "Prokaryotic DNA Polymerases". Cells lacking Pol I have been found suggesting Pol I activity can be … POL α is a members of Family B Polymerases and are the main polymerases involved with nuclear DNA replication. The replication of E. coli DNA requires at least 30 proteins. C. The lagging strand is made of a series of pieces that must be joined together to make a continuous strand D. The two strands of parental DNA are separated during DNA replication E. DNA polymerase builds a new strand by adding DNA … Since we know that nucleic acids are polymerized by adding the 5’ phosphate of a new nucleotide to the 3’ hydroxyl of the previous nucleotide (5’ to 3’, in green), this means that one of the strands, called the leading strand, is being synthesized in the same direction that the replication machine moves. Most eukaryotes solve the problem of synthesizing this unreplicated DNA with a specialized DNA polymerase called telomerase, in combination with a regular polymerase. YES: In DNA, the proportion of adenine always equals that of thymine, and the proportion of guanine always equals that of cytosine. 1983 Jan 15;39(1):1-25. Step 5: After DNA synthesis by DNA pol III, DNA polymerase I uses its 5’-3’ exonuclease activity to remove the RNA primer and fills the gaps with new DNA. (2019, February 26). In order for the template strand that is 5’ to 3’ from left to right to be replicated, the strand must be fed into the polymerase backwards. The polymerase activity then adds new DNA nucleotides to the upstream Okazaki fragment, filling in the gap created by the removal of the RNA primer. The next important enzyme is DNA polymerase III, also known as DNA pol III, which adds nucleotides one by one to the growing DNA chain (Figure 2). This site complies with the HONcode standard for trustworthy health information: verify here. For more information contact us at [email protected] or check out our status page at https://status.libretexts.org. DNA polymerase 3 is also called as holoenzyme and it is the most essential component of replisome. https://www.news-medical.net/life-sciences/Prokaryotic-DNA-Polymerases.aspx. Pol I is also involved in the basic mechanism of DNA replication, primarily to fill in gaps created during lagging strand synthesis (defined 3 pages ahead) or through error-correcting mechanisms. PHAR 2811 Dale’s lecture 5 page 4 Protein Prokaryotic/ eukaryotic Activity/role DNA Polymerase I Prokaryotic 5’ to 3’ polymerase, 3’ to 5’ exonuclease, 5’ to 3’ exonuclease DNA Polymerase III Prokaryotic 5’ to 3’ polymerase, 3… After the telomerase has made the first strand a primase synthesizes an RNA primer and a regular DNA polymerase can then make a complementary strand so that the telomere DNA will ultimately be double stranded to the original length. Single-Strand Binding (SSB) Protein. Pol II is a family B polymerase and provides support to Pol III. 3: Do not form the typical chromosome. Chromosome replication begins with the binding of the DnaA initiator protein to an AT-rich 9-mer in OriC and melts (disrupts the hydrogen bonding between) the two strands. Eukaryotic cells use polymerase I to remove the RNA primers. This produces two new double-stranded molecules from one double helix. [ "article:topic", "authorname:swleacock" ], 1.4: In vitro applications of DNA replication, Experiment that demonstrated semiconservative DNA replication, Obstacle #2: Make two strands in opposite directions at the same time, https://bio.libretexts.org/Bookshelves/Cell_and_Molecular_Biology/Book%3A_Cells_-_Molecules_and_Mechanisms_(Wong)/7%3A_DNA/7.3%3A_Prokaryotic_Replication. DNA Replication Eukaryotes Vs Prokaryotes DNA replication happens in both Prokaryotes and Eukaryotes before cell division, the process allows for both cells to get an extra copy of its genetic material of their parent cell. When the cell enters S (synthesis) phase in the cell cycle (G1-S-G2-M) all the chromosomal DNA is replicated. By continuing to browse this site you agree to our use of cookies. It attached the deoxyribo nucleotide to the 3’-OH group of RNA/DNA primer. It also requires a free 3′-OH group to which it can add nucleotides by forming a phosphodiester bond between the 3′-OH end and the 5′ phosphate of the next nucleotide. Most abundant polymerase accounting for >95% of polymerase activity in E. coli. Enzymes called DNA polymerases synthesize new strands by adding nucleotides to the 3'-OH group present on the previous nucleotide. In its most active form it is associated with nine (or) more other proteins to form the “Pol III HOLOENZYME”, occasionally termed Pol III. News-Medical talks to Dr. Pria Anand about her research into COVID-19 that suggests neurologic complications are common even in mild infections. Other DNA polymerases are involved in the repair, proofreading and primer removal. In eukaryotes, DNA polymerase is the main enzyme for replication. A bacterial chromosome is a covalently closed circle that, unlike eukaryotic chromosomes, is not organized around histone proteins. Eukaryotic cells have multiple DNA polymerases. Summarize the process of DNA replication, including bidirectional synthesis and explain the Meselson-Stahl experiment that demonstrated semiconservative replication. Please note that medical information found DNA polymerase II and the recently discovered Pol IV and Pol V do not participate in chromosomal replication, but rather are used to synthesize DNA when certain types of repair is needed at other times in the cellular life cycle. The DNA polymerase only inserted nucleotides once it finds the free 3’ OH end facilitated by … Activities found in DNA pol-I: 1. Its main function is excision repair of DNA strands from the 3′-5′ direction to the 5′-3 direction, as an exonuclease. The other strand is problematic: looked at linearly, the newly synthesized strand would be going 3’ to 5’ from left to right, but DNA polymerases cannot add nucleotides that way. 5. It has 5′ to 3′ polymerase activity. Cells that lack dinB are at an increased risk of developing mutations caused by agents that damage DNA. DNA polymerase 3 possesses 5’ to 3’ polymerization activity where new nucleotides are added to the growing chain at its 3’ end. Owned and operated by AZoNetwork, © 2000-2020. 26 December 2020. DNA polymerases are unable to join two individual free nucleotides together to begin forming a nucleic acid; they can only add onto a pre-existing strand of at least two nucleotides. The first problem is resolved by DNA polymerase I. DNA replication in both prokaryotes and eukaryotes begins at an Origin of Replication (Ori). DNA replication in eukaryotes takes a much longer time than DNA replication in prokaryotes. The complex has high processivity (i.e. Eukaryotic DNA polymerase POL α . The transcription elongation phase begins with the release of the σ subunit from the polymerase. This interferes with the processivity of Pol III which acts as a checkpoint, stopping replication and allowing time for DNA to be repaired. The RNA in human telomerases uses the sequence 3-AAUCCC-5' as the template, and thus our telomere DNA has the complementary sequence 5'-TTAGGG-3' repeated over and over 1000’s of times. DNA molecules are the troves of genetic information of an organism. This enzyme has one simple but crucial task: it catalyzes the attack of the 3’-OH from one fragment on the 5’ phosphate of the next fragment, generating a phosphodiester bond. oligonucleotide of RNA with free 3´ hydroxyl group), a template (i.e single-stranded DNA), and deoxyribonucleotides (d ATP, d CTP, d GTP, and d TTP) in order to function. Mechanism for overcoming “stalled” polymerase during elongation B. So, in the single-stranded region trailing the helicase, if we look left to right, one template strand is 3’ to 5’ (in blue), while the other is 5’ to 3’ (in red). Rho dependent termination – Pol V also belongs to the Y family of polymerases and allows DNA damage to be bypassed in order for replication to continue. Transcription complex dissociates and RNA pol and nascent RNA released 3. It … How do cells resolve this problem? For this reason, they are said to work in a 5' to 3' direction. 4 The smallest aggregate having enzymatic activity is called the “CORE ENZYME”. The RNA polymerase activity is a primase. Each subunit has a unique role; the two α-subunits are necess… Prokaryotic DNA Polymerase-III is a very complex enzyme. A … Determine whether the characteristics describe DNA replication in prokaryotes only, eukaryotes only, or both prokaryotes and eukaryotes. This enzyme belongs to the Y family of DNA polymerases. In prokaryotes, DNA replication is the first step of cell division, ... as against the unidirectional activity of the DNA polymerase. No problem there. The DNA polymerase cannot initiate the replication process without any help; on the other hand, RNA polymerase can initiate the transcription process without any help. All known DNA polymerases catalyze the synthesis of DNA in the 5′ to 3′ direction, and the nucleotide to be added is a deoxynucleoside triph… On the other hand, DNA Polymerase 3 is vital for prokaryotic DNA replication. It is found in both prokaryotes and eukaryotes. Summary of Proteins associated with DNA Replication in both Prokaryotes and Eukaryotes . It is the first polymerase enzyme that was discovered by Arthur Kornberg in 1958. The replication machine consists of the helicase, primases, and two DNA polymerase III holoenzymes moving in the same physical direction (following the helicase). DNA Polymerase I. Although the loss of such a small sequence would not be a problem, the continued rounds of replication would result in the continued loss of sequence from the chromosome end to a point were it would begin to loose essential gene sequences. DNA polymerase III involves in bulk respiration. NAD+ Metabolism in Cancer and Cancer Therapies, A short-cut in photosynthetic machinery can allow needles of pine trees to stay green, Molecular reporters produce fluorescence to expose the allies of tumor cells, Researchers develop a harmless air sterilization prototype to kill microbes, Transcription factors in the brain strongly correlate with the behavior of honey bees, Study shows neuropeptide corazonin regulates the release of diapause hormone in silkworms. The answer to this question was elucidated by classic experiments by Meselson and Stahl. Because DNA is double stranded, each strand needs to be used as a template, but these strands are antiparallel. This unique enzyme has two distinct polymerase activities: a 5’- 3’ DNA-dependent DNA polymerase, and a 5’- 3’ DNA-dependent RNA polymerase. DNA polymerase III holoenzyme is the primary enzyme complex involved in prokaryotic DNA replication. Watch the recordings here on Youtube! on this website is designed to support, not to replace the relationship this video describes the reaction mechanism of DNA polymerase in bacteria Prokaryotes contain five different types of DNA polymerase. Prokaryotic DNA Polymerases. Note: the number of repeats, and thus the size of the telomere, is not set. Helicases are the enzymes that help in unwinding both the strands of DNA for the process … News-Medical speaks to Dr. Jaswinder Singh about his research surrounding why some groups are more susceptible to severe cases of COVID-19. In E. coli, the polymerase is composed of five polypeptide subunits, two of which are identical. Figure 1: DNA replication in prokaryotes, which have one circular chromosome. It has 3′ to 5′ exonuclease activity (proofreading) It has DNA Repair activity. The 5’-3’ exonuclease binds to double- stranded DNA that has a single-stranded break in the phosphodiester backbone such as what happens after Okazaki fragments have been synthesized from one primer to the next, but cannot be connected. The two template DNA strands have opposing orientations: one strand is in the 5' to 3' direction and the other is oriented in the 3' to 5' direction. Dependent on specific DNA sequences (terminator) 2. Primase: This enzyme activity catalyzes the synthesis of RNA primers to initiate DNA replication. Even though the RNA has been replaced with DNA, this still leaves a fragmented strand. Pilot Proteins 6. The enzyme that builds the complementary strand using the template strand as a guide is polymerase III. A digital CRISPR-based method for quick detection and absolute quantification of SARS-CoV-2, http://www-lehre.img.bio.uni-goettingen.de/, http://dnareplication.cshl.edu/content/free/chapters/15_wang.pdf, www.informatics.indiana.edu/.../lecture_notes_19b.pdf, Researchers discover how shattered chromosomes make cancer cells more aggressive, Mother's diet while breastfeeding can shape the profile of human milk oligosaccharides, Study clarifies the effect of aging on hematopoietic stem cells, New drug starves cancer cells by attacking mitochondria, Researchers use precision medicine strategy to identify a new genetic skeletal disorder, Cadmium linked to more severe flu and pneumonia infections. Since Arthur Kornberg was awarded the Nobel Prize in 1959 for determining the roles of DNA polymerases during DNA replication, it has been widely accepted that the DNA polymerases involved in this process require a single-stranded template to construct a new DNA strand. B. DNA ligase adds nucleotides to the lagging strand. DNA polymerase is able to add nucleotides only in the 5′ to 3′ direction (a new DNA strand can be only extended in this direction). We will discuss DNA replication in prokaryotes in different steps to make it easier to understand. DNA chain growth is in the 5’ to 3’ direction with addition at the 3’ hydroxyl end. DNA polymerases not only helps in synthesising new strand of DNA but it have other main functions too. This is a type A or Family A polymerase enzyme that was initially isolated from E. coli and most abundantly found in E. coli. Pol IV is an error-prone polymerase that has no 3’ to 5’ proofreading activity and is involved in mutagenesis or the altering of DNA to give rise to a mutation. DNA polymerase I participates in the DNA replication of prokaryotes. Helicase. The proofreading exonuclease acts just like it does for Pol III, immediately removing a newly incorporated incorrect nucleotide. Note that the energy is provided by the nucleotide triphosphate itself; two phosphates are released and one phosphate remains as a part of the phosphodiester bond. Most abundant polymerase accounting for >95% of polymerase activity in E. coli. The factor nusA is involved in the function of elongation as well as chain termination. DNA polymerase adds new free nucleotides to the 3’ end of the newly-forming strand, elongating it in a 5’ to 3’ direction. Wong, Cells - Molecules and Mechanisms (https://bio.libretexts.org/Bookshelves/Cell_and_Molecular_Biology/Book%3A_Cells_-_Molecules_and_Mechanisms_(Wong)/7%3A_DNA/7.3%3A_Prokaryotic_Replication). DNA polymerase III involves in bulk respiration. Mandal, Ananya. Have questions or comments? Primase 3. In prokaryotes, DNA polymerase III is the main enzyme responsible for replication. Three different prokaryotic DNA polymerases are known, of which DNA polymerases I and II are meant for DNA repair and DNA polymerase IN is meant for actual DNA replication, (i) DNA polymerase I (isolated around 1960 by Arthur Kornberg) was the first enzyme suggested to be involved in DNA replication. ; Both are DNA-directed RNA polymerases. Eukaryotic cells must replicate the mitochondrial DNA with polymerase gamma. The term holoenzyme refers to an enzyme that contains several different subunits and retains some activity even when one (or) more subunits is missing. Therefore, a specialized RNA polymerase (RNAP’s do not have this limitation) known as primase is a part of the replisome, and reads creates a short RNA strand termed the primer for the DNA polymerase to add onto. YES: DNA is composed of 3 basic components: five-carbon sugars, phosphate groups, and 4 different nitrogenous bases. DNA polymerase plays a central role in process of life and carries a weighty responsibility of making an accurate copy of the cell's … Retrieved on December 26, 2020 from https://www.news-medical.net/life-sciences/Prokaryotic-DNA-Polymerases.aspx. Because there are many repeats at the end, this fluctuation maintains a length buffer – sometimes it’s longer, sometimes it’s shorter – but the average length will be maintained over the generations of cell replication. I will compare their characteristics and explain the process of DNA replication of prokaryotes and Eukaryotes. For example, E. coli has a ~4.5 Mb genome (chromosome) that can be duplicated in ~40 minutes assuming a single origin, bi-directional replication, and a speed of ~1000 bases/second/fork for the polymerase. DNA polymerase 1, 2 and 3 of prokaryotes and DNA polymerase of eukaryotes are similar in structure and mechanism. Replication starts at a single origin (ori C) and is bi-directional and semi-conservative. This leads to two major problems: first, there are little bits of RNA left behind in the newly made strands (just at the 5’ end for the leading strand, in many places for the lagging); and second, Pol III can only add free nucleotides to a fragment of single stranded DNA; it cannot connect another fragment. Mandal, Ananya. Termination in prokaryotes 1. Difference in function. From: Molecular Biology (Second Edition), 2013. DNA polymerase 3 is essential for pro-karyotic DNA replication and was discovered by Thomas Kornberg and Malcolm Gefter. DNA polymerase I (or Pol I) is an enzyme that participates in the process of prokaryotic DNA replication.Discovered by Arthur Kornberg in 1956, it was the first known DNA polymerase (and the first known of any kind of polymerase).It was initially characterized in E. coli and is ubiquitous in prokaryotes.In E. coli and many other bacteria, the gene that encodes Pol I is known as polA. The enzymes are: 1. The core and the beta sliding clamp are present in duplicate, to allow for processing of both the leading and lagging DNA strands. In prokaryotes, elongation proceeds bidirectionally until the replication forks meet. The DNA is circular, double-stranded and found in the cytoplasm. Each process has its differences and similarities. A single origin of replication results in the formation of two replication forks. Thus, eukaryotes contain multiple origins of replication distributed over the length of each chromosome to enable the duplication of each chromosome within the observed time of S-phase (Fig 2.9).