1S

Presented By: Mohsin Shad (2013-Bc-005) Asmat Shahzad (2013-Bc-026) Muhammad Zulqarnain (2013-Bc-027) Hamza Zafar (2013-Bc-032)

Presented To : Miss Huma Mujahad

2DNA AND RNA POLYMERASES

3DNA Polymerases

• The enzymes that create DNA molecules by assembling nucleotides• These enzymes are essential to DNA replication • They usually work in pairs to create two

identical DNA strands from a single original DNA molecule• There are three main types of prokaryotic DNA polymerases• DNA polymerases I• DNA polymerases II• DNA polymerases III

4DNA Polymerases I

• DNA Polymerases I was firstly discovered in 1958 by Arthur Kornberg who received Noble Prize in Physiology and Medicine in 1959• DNA Polymerases I is mainly responsible for:• Proofreading of DNA strand• Repairing of damage DNA• Filling the gap between the okazaki fragments• Removal of RNA primer

5DNA Polymerases II

• DNA Polymerases II was identified later during the experiment on mutant E.coli cell line• DNA Polymerases II have temporary function

when DNA Polymerases I and DNA Polymerases III are not functional• Still capable for doing synthesis on damage

template• Participating in DNA repairing

6DNA Polymerases III

• DNA Polymerases III was identified later during the experiment on mutant E.coli cell line.• DNA Polymerases III is heterodimer enzyme

composed of ten different subunits• It is true enzyme that is responsible for the

elongation process• It also responsible for the polymerization of

Nucleotide and make most of the DNA during replication.

7How DNA Polymerases I and III Work ?

8Eukaryotic DNA Polymerases

• 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 d: 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.

9Eukaryotic DNA polymerases

10How Eukaryotic DNA Polymerases Work

11RNA Polymerase

• Enzyme that synthesizes RNA using a DNA template through a process called transcription• RNA polymerase enzymes are essential to life and

are found in all organisms and many viruses• It polymerizes ribonucleotide at the 3 end of an

RNA transcript

12Bacterial RNA Polymerases

• RNA polymerases is enzyme that synthesizes RNA using a DNA template • In bacteria only one RNA polymerases is

participate in transcription• Bacterial RNA polymerases has four subunit.• The sigma subunit of bacterial RNA polymerases

recognized promoter• In bacteria it form monocistronic and polycistronic

mRNA

13Subunits Of RNA Polymerase's

14How RNA Polymerases work in Bacteria ?

15Eukaryotic RNA Polymerases

There are three types of RNA polymerases used for eukaryotic transcription• RNA polymerase I Eukaryotic RNA polymerase that

transcribes the genes for the large ribosomal RNAs• RNA polymerase II Eukaryotic RNA polymerase

that transcribes the genes encoding proteins• RNA polymerase III Eukaryotic RNA polymerase

that transcribes the genes for 5S ribosomal RNA and transfer RNA

16Prokaryotic vs Eukaryotic RNA Polymerases

17How RNA Polymerases work in Eukaryotic ?

18 Any Question ?

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