Your SlideShare is downloading. ×
0
Enzymes and protiens involved in dna replication by datha
Enzymes and protiens involved in dna replication by datha
Enzymes and protiens involved in dna replication by datha
Enzymes and protiens involved in dna replication by datha
Enzymes and protiens involved in dna replication by datha
Enzymes and protiens involved in dna replication by datha
Enzymes and protiens involved in dna replication by datha
Enzymes and protiens involved in dna replication by datha
Enzymes and protiens involved in dna replication by datha
Enzymes and protiens involved in dna replication by datha
Enzymes and protiens involved in dna replication by datha
Enzymes and protiens involved in dna replication by datha
Enzymes and protiens involved in dna replication by datha
Enzymes and protiens involved in dna replication by datha
Enzymes and protiens involved in dna replication by datha
Enzymes and protiens involved in dna replication by datha
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×
Saving this for later? Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime – even offline.
Text the download link to your phone
Standard text messaging rates apply

Enzymes and protiens involved in dna replication by datha

3,028

Published on

Published in: Technology
0 Comments
4 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total Views
3,028
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
150
Comments
0
Likes
4
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 1. 1 ENZYMES AND PROTIENS INVOLVED IN DNA REPLICATION Presentation on Submitted to: Dr. K. Jeevaratnam, Professor, DBMB. Submitted By: B.Devadatha, Reg no. 1236829, DBMB. Subject: Molecular Biology
  • 2. Index Content Slide no dnaA Protein 3 DNA Helicase 4 Single-strand- binding protein (SSBP) 5 Primase 6 DNA Polymerase III 7 DNA polymerase I 9 DNA ligase 10 Topoisomerase ІІ 11 Topoisomerase І 12 Differences between prokaryotic and eukaryotic enzymes 13 Reference 15 2
  • 3. dnaA Protein  Recognizes ori C sequence.  Binds to 9mers sequences forming an Initiation complex. Melts DNA strands at oriC 13mers in presence of ATP to form open complex. 3
  • 4. DNA Helicase  Opens up the duplex at the replication fork to provide a single stranded template.  Helicase uses energy from the ATP to break the hydrogen bonds holding the base pairs together.  Shows processivity and polarity.  E. coli contains at least 6 different helicases--some involved in DNA repair and others in conjugation, the principal helicase in DNA replication is DnaB. 4
  • 5. Single-strand- binding protein (SSBP)  Single-strand- binding protein (SSB) binds to the single-stranded portion of each DNA strand, inhibiting the strands from reannealing and protecting them from degradation by nucleases.  E.Coli SSBP is a tetramer and cooperatively in sequence independent manner.  In eukaryotic cells, a heterotrimeric protein called replication factor A serves the role of SSB in DNA replication. 5
  • 6. Primase Primase synthesizes a short (about 10 nucleotides) RNA primer in the 5‟ 3‟ direction to prime DNA chain elongation. RNA primers are required because DNA polymerases are unable to initiate synthesis of DNA, but can only extend a strand from the 3' end of a preformed “primer”. Korenberg coined the term primosome to refer to collection of protiens needed to make primers. 6
  • 7. DNA Polymerase III DNA pol III Holoenzyme is major replicative polymerase for both leading and lagging strand synthesis. DNA polymerase III begins synthesizing DNA in the 5‟ 3‟direction, beginning at the 3‟ end of each RNA primer. This is a multiprotein complex that consists of 10 distinct polypeptides. Hallmarks of pol III are its very high catalytic potency and processivity. 7
  • 8.  Catalytic core of DNA pol III composed of α ,ε θ- subunits ,contains the polymerase activity and a 3‟  5‟ exonuclease for proofreading.  A dimer of β-subunit forms a ringshaped structure and act as sliding clamp.  The ϒ-complex is a group of five proteins that comprise clamp loader; the clamp loader places the clamp on DNA.  Two core proteins are bound together by τ-subunit.  In eukaryotic cells, a multi-subunit protein called replication factor C (RF-C) is the clamp loader, and proliferating cell nuclear antigen (PCNA) is the sliding clamp. Clamp and clamp loader 8
  • 9. DNA polymerase I DNA polymerase I and RNAse H are involved in removing RNA primers in the processing of DNA after replication. This enzyme removes the ribonucleotides one at a time from the 5' end of the primer (5„ 3' exonuclease). DNA polymerase I also fills in the resulting gaps by synthesizing DNA, beginning at the 3' end of the neighbouring Okazaki fragment. Both DNA polymerase I and III have the ability to "proofread" their work by means of a 3' 5' exonuclease activity. Proteases such as subtilisin or trypsin cleave DNA pol І into two fragments Klenowfragment and a smaller N-terminal fragment. 9
  • 10.  DNA ligase seals the "nicks" by forming phosphodiester bonds between the 3„OH and 5‟phosphate of adjacent Okazaki fragments, converting them to a continuous strand of DNA.  The ligase enzyme from Ecoli requires NAD as a cofactor, where as that of Viruses and Eukaryotes requires ATP. DNA ligase 10
  • 11. Topoisomerase ІІMake a transient double- strand break in the helix and forms a covalent linkage. DNA gyrase can introduce negative supercoils into DNA using ATP. GyrA subunit cuts and rejoins the DNA. GyrB subunit provides energy by ATP hydrolysis. Inhibited by Nalidixic acid and Novobiocin. 11
  • 12. Topoisomerase І Produces a transient single strand break forming 5‟phospho tyrosine linkage. Reactions catalyzed: Relaxation. Knotting/unknotting. Catenation/decatenation. 12
  • 13. DNA pol 111 is involved in invivo replication of DNA. DNA pol 1 is the repair enzyme. Primase synthesizes primer in Ecoli. DNA pol α and δ are involved in invivo replication of nuclear DNA where as DNA pol gama for mitochondrial DNA. DNA pol beta and Є functions as DNA repair enzyme. DNA pol α synthesizes primers for both leading and lagging strands. Prokaryotes Eukaryotes Differences between prokaryotic and eukaryotic enzymes 13
  • 14. In Ecoli SSB protiens are present. β subunit of DNA pol 111 acts clamp Gama subunit of DNA pol 111 acts as clamp loading factor. DNA helicase is associated with DNA pol111. Eukaryotic topoisomerase 1 relaxes both positive and negative supercoils. RF-A is the eukaryotic SSB. PCNA acts as clamp. RF-C acts as clamp loading factor. DNA helicase A is associated with DNA α , and DNA helicase Є is associated with DNA pol Є Prokaryotes Eukaryotes 14
  • 15.  Text book of Molecular Biology By David Clark Genes VII  Text book of Lehninger Principles of Biochemistry, Fourth Edition - David Reference 15
  • 16. 16

×