A DNA polymerase is a member of a family of enzymes that catalyze the synthesis of DNA molecules from nucleoside triphosphates, the molecular precursors of DNA. These enzymes are essential for DNA replication and usually work in groups to create two identical DNA duplexes from a single original DNA duplex. During this process, DNA polymerase "reads" the existing DNA strands to create two new strands that match the existing ones.[1][2][3][4][5][6] These enzymes catalyze the chemical reaction deoxynucleoside triphosphate + DNAn ⇌ pyrophosphate + DNAn+1. DNA polymerase adds nucleotides to the three prime (3')-end of a DNA strand, one nucleotide at a time. Every time a cell divides, DNA polymerases are required to duplicate the cell's DNA, so that a copy of the original DNA molecule can be passed to each daughter cell. In this way, genetic information is passed down from generation to generation. Before replication can take place, an enzyme called helicase unwinds the DNA molecule from its tightly woven form, in the process breaking the hydrogen bonds between the nucleotide bases. This opens up or "unzips" the double-stranded DNA to give two single strands of DNA that can be used as templates for replication in the above reaction.

1. DNA POLYMERASE

2. Content
 Introduction
 Definition
 Types
 Working process
 Functions

3. Introduction
 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.
 Each of these types plays a major role in replication and DNA
repair mechanisms.

4. Definition
 “DNA polymerases are enzymes that catalyze the template-
directed synthesis of DNA.”
 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.

5. Types of DNA Polymerase
Prokaryotic DNA polymerase:-
 DNA polymerase l
 DNA polymerase ll
 DNA polymerase lll
 DNA polymerase lV
 DNA polymerase V

6.  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 ll:- Pol II has 3’-5’ exonuclease activity and participates in DNA
repair. Pol II is also thought to be a backup to Pol III as it can interact with
holoenzyme proteins and assume a high level of processivity.
 DNA polymerase lll :- is the main enzyme for replication in E.coli. 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.

7. Cont…

8. Cont….
 DNA Polymerase lV :- DNA polymerase involved in non-
targeted mutagenesis.
During SOS induction, Pol IV production is
increased tenfold and one of the functions during this time is to
interfere with Pol III holoenzyme processivity.
 DNA polymerase V:- Pol V is a Y-family DNA polymerase that is
involved in SOS response and translesion synthesis DNA
repair mechanisms.

9. How Prokaryotic DNA polymerase works

10.  Eukaryotic DNA polymerase:-
 DNA polymerase a :- Enzyme that makes short segment
of initiator DNA during replication of animal chromosomes.
 DNA polymerase β: -Implicated in repairing DNA, in base
excision repair and gap-filling synthesis.
 DNA polymerase γ: - Replicates and repairs mitochondrial
DNA and has proofreading 3’->5’ exonuclease activity.
 DNA polymerase δ :- Enzyme that makes most of the
DNA when animal chromosomes are replicated.
 DNA polymerase ε: -Also highly possessive and has
proofreading 3’->5’ exonuclease activity

11. How eukaryotic DNA polymerase works

12. Functions
 Replication:- The main function of the DNA polymerase is to
synthesize DNA by the process of replication
 Repair:- s, 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.
 Proofreading:- 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.