DNA POLYMERASE

DNA polymerases are a group of enzymes that are used to make copies of DNA templates, essentially used in DNA replication mechanisms. These enzymes make new copies of DNA from existing templates and also function by repairing the synthesized DNA to prevent mutations. DNA polymerase catalyzes the formation of the phosphodiester bond which makes up the backbone of DNA molecules. It uses a magnesium ion in catalytic activity to balance the charge from the phosphate group.

1. DNA AND RNA POLYMERASE PREPARED BY; MISS RABIA KHAN BABER

2. AIMS AND OBJECTIVES OF PPT

3. DNA POLYMERASE DNA polymerases are a group of enzymes that are used to make copies of DNA templates, essentially used in DNA replication mechanisms. These enzymes make new copies of DNA from existing templates and also function by repairing the synthesized DNA to prevent mutations. DNA polymerase catalyzes the formation of the phosphodiester bond which makes up the backbone of DNA molecules. It uses a magnesium ion in catalytic activity to balance the charge from the phosphate group.

4. DISCOVERY DNA polymerase was first identified by Arthur Kornberg in lysates of  Escherichia coli , in 1956. The enzyme is found and used in the DNA replication of both prokaryotic and eukaryotic cells. Several types of DNA polymerase enzymes have been discovered with the first one to be discovered named DNA polymerase I.

5. ROLE AND FUNCTION Each of these types plays a major role in replication and DNA repair mechanisms. However, DNA polymerases are not used for initiating the synthesis of new strands, but in the extension of already existing DNA or RNA strands which are paired with a template strand. DNA polymerase starts its mechanism after a short RNA fragment is known as a primer is created and paired with a template DNA strand. DNA polymerase acts by synthesizing the new DNA strand by adding new nucleotides that match those of the template, extending the 3′ end of the template chain. Each nucleotide is linked with a phosphodiester bond.

6. The DNA polymerase uses energy from the hydrolysis of the bond that is between the three phosphates attached to each nucleotides. The addition of a nucleotide to a growing DNA strand forms a phosphodiester bond between the phosphate of the nucleotide to the growing chain using the high-energy phosphate bond of hydrolysis, releasing two distal phosphates known as pyrophosphate. DNA polymerases are very accurate in their mechanism with minimal errors of less than one error for every 10 6  nucleotides.

7. Some types of DNA polymerase have the ability to proofread and remove unmatched bases of nucleotides and correct them. They also correct post-replication mismatches by monitoring and repairing the errors, by distinguishing mismatches of the new strand from the template strand sequences. 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. Polymerase α and δ are majorly applied and active in diving cells hence involved in replication while polymerase β is active in both diving and nondividing cells hence it is involved in the repair of DNA damage.

8. EUKARYOTIC DNA POLYMERASE DNA Polymerases play a key role in the synthesis of DNA. These polymerases are multi-subunit complexes that function very uniquely. It requires different components to work together to function efficiently. Polymerases act upon single-stranded strands to synthesize a strand that is complementary. In eukaryotic cells, there are 5 families of DNA polymerase. These can encode into different enzymes. Critical for DNA replication are three DNA polymerases: Polymerase α-primase, Polymerase δ, and Polymerase ε. These three polymerases function at the replication fork of the DNA strands. The DNA strands are by helicase . It is Polymerase α- primase that initiates replication on the leading and lagging strand. It is here that the RNA primers (about 10 nucleotides) are laid down.

9. DNA POLYMERASE FAMILY FAMILY A Includes DNA polymerase I FAMILY B Includes all eukartyotic DNA polymerase s involved in chromosomal replication FAMILY X Includes all enzyme responsible for the repair or specialized type of DNA replication. FAMILY Y RT FAMILY

10. DNA POLYMERASE TYPES-FAMILY A Polymerase γ Polymerase γ is a Type A polymerase, whose main function is to replicate and repair mitochondrial DNA. It also functions by proofreading 3′ to 5′ exonuclease activity. Mutations on Poly γ significantly affect the mitochondrial DNA causing autosomal mitochondrial disorders.

11. DNA POLYMERASE TYPES-FAMILY B Polymerase α, Polymerase δ, and Polymerase ε These are the type B Polymerase enzymes and they are the main polymerases applied in DNA replication. Pol α works by binding to the primase enzyme, forming a complex, where they both play a role in initiating replication. Primase enzyme creates and places a short RNA primer which allows Pol α to start the replication process. Pol δ starts the synthesis of the lagging strand from Pol α, while Pol ε is believed to synthesize the leading strand during replication. Studies indicate that Pol δ replicates both the lagging and leading strand. Pol δ and ε also have a 3′ to 5′ exonuclease activity.

12. DNA POLYMERASE TYPES-FAMILY X Polymerase β, Polymerase μ, and Polymerase λ These are type 3 or Family X of polymerase enzymes. Pol β has a short-patch base excision repair mechanism where it repairs alkylated or oxidized bases. Pol λ and Pol μ are important for rejoining DNA double-strand breaks due to hydrogen peroxide and ionizing radiation, respectively.

13. DNA POLYMERASE TYPES-FAMILY Y Polymerases η Polymerase η functions by accurately ensuring the translesion synthesis of DNA damages that is caused by ultraviolet radiation.

14. S.No# CHARACTERISTICS DNA POLYMERASE RNA POLYMERASE 1.       DEFINITION It is an enzyme that synthesizes the DNA It is an enzyme synthesizes the RNA 2.       MECHANISM DNA polymerase’s mechanism is during replication whereby it synthesizes new DNA strands RNA polymerase functions during transcription, which is the synthesis of RNA 3.       STRANDS It synthesizes a double-stranded DNA molecule It synthesizes a single-stranded RNA molecule 4.       PRESENCE OR ABSENCE OF PRIMER Its replication mechanism is initiated by a short-RNA primer It does not need a primer to initiate transcription 5.       NUCLEOTIDE INSERTION It inserts nucleotides after finding the free 3’ OH end by the assistance of the primer-synthesizer, primase enzyme It adds nucleotides directly. 6.       BASE PAIRS It adds Adenine-Thymine and Guanine-Cytosine base pairs It adds Adenine- Uracil and Guanine-Cytosine base pairs

15. CONT.. 7.       FUNCTIONALITY It has polymerization and proofreading activity RNA polymerase only has a polymerization activity. 8.       POLYMERIZATION RATE The rate of polymerization by DNA polymerase is about 1000 nucleotides per second in prokaryotes The rate of RNA polymerase is 40 to 80 nucleotides per second. 9.       EFFICIENCY DNA polymerase enzyme is faster, efficient, and more accurate considering its proofreading activity. RNA polymerase is slower, inefficient, and inaccurate. 10.     TERMINATION The DNA synthesis continues until the end when the strand ends, that is when polymerization stops, thus the entire chromosomal DNA is synthesized. The polymerization is terminated when RNA polymerase finds the stop codon or termination codon on the nucleic acid strand.

16. THANKYOU !!