Molecular Biology Tutorials

Nucleotide Excision Repair (NER) in Prokaryotes (DNA Repair Mechanism: Part IV)

The UvrABC Endonuclease (Excinuclease) Repair of DNA in Prokaryotes


What is Nucleotide Excision Repair (NER)?

As the name suggests it is a type of DNA repair mechanism. In nucleotide excision repair or NER, the damaged base along with a short stretch of healthy strand is removed and later the gap is refilled with correct nucleotides. Thus the NER pathway operates by ‘cut and patch’ mechanism. Even though nucleotide excision repair mechanism is present in prokaryotes and eukaryotes, the components of the pathways in both groups shows considerable variations. The prokaryotes shows relatively simple nucleotide excision repair mechanism, where as in eukaryotes, the NER pathway is quite complex with many enzymes.

UvrABC Excinuclease repair

Image source: wikipedia

Nucleotide Excision Repair can repair a variety of bulky lesions of the DNA such as pyrimidine dimers formed by UV irradiation and it can also remove chemically modified bases.

Classification of NER:

(1). UvrABC Endonuclease NER in Prokaryotes

(2). NER in Eukaryotes

There are two types of NER mechanism in eukaryotic cells

(a). Transcription Coupled Nucleotide Excision Repair (TC-NER)

(b). Global Genomic Nucleotide Excision Repair (GG-NER)

In this post, we will discuss only the NER mechanism of prokaryotes. The NER mechanism in prokaryotes is better known as UvrABC Endonuclease repair.

Enzymes involved in NER pathway of prokaryotes:

Nucleotide excision repair pathway in prokaryotes is orchestrated by UvrABC endonuclease complex. The NER method is also assisted by DNA polymerase I and DNA ligase enzymes. UvrABC endonuclease complex is a special class of endonuclease enzyme involved in DNA repair of prokaryotes. The name is derived from the root term ultraviolet radiation, since the level of most of these enzymes will be elevated in the bacterial cells when the cells are exposed to UV light.

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Molecular Biology Tutorials

DNA Repair Mechanism – Part I Introduction (DNA Damaging Agents, DNA Damages and Recovery of DNA Damages)


Introduction to DNA Repair Mechanisms

“Genetic variation is important for evolution, but the survival of the individuals
demand genetic stability”

What is DNA repair?

DNA is the genetic information carrier molecule in the cell and thus it is very essential to keep the genetic information intact. Even though DNA holds a prime position, it is one of the highly susceptible molecules in the cells because DNA can be damaged by a number of factors both internal and external in origin. It is very surprising to know that, our cells lose approximately 5000 nucleotides every day due to different damages of the DNA. If these damages are not rectified properly, our cells will be subjected to severe mutations and that will be fatal for the survival of the individual cells and the organism itself. DNA replication process in the cell which ensures the production of exact copy of the genetic information is very accurate due to the high fidelity of DNA polymerase enzyme. However, the process of DNA replication is not 100 percent error free. DNA polymerase enzyme sometimes accidentally introduces wrong bases which will disrupt the normal Watson-Crick base paring of the DNA. There are also many possibilities of DNA damage during genetic recombination happens during gametogenesis by meiotic cell division. If the damages or errors in the DNA are not corrected in the somatic cells, it may leads to the development of cancer or it results in the loss of function of genes. More than that, if DNA damages occur in the gametes is not rectified, it will be carried over to next generation through progenies. Thus, damage to the genetic materials is a major threat to all organisms. In order to counteract these threats, cells has evolved many methods to overcome and rectify different types DNA damages. All these methods are collectively termed as DNA REPAIR mechanisms. Similar to DNA replication, transcription and translation, the process of DNA repair is also a prime molecular event in the cells which is very essential for the ultimate survival of the cells and also for the survival of the organism.

DNA Repair and Nobel Prize in Chemistry (2015)

DNA Repair Mechanism

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mcq biology

DNA Repair Mechanisms: Biology MCQ 019 with Answer Key (Model Questions for CSIR NET and GATE Life Sciences Examination, December 2015)

MECHANISTIC STUDIES OF DNA REPAIR

1. Which of the following DNA repair mechanism is known as the ‘cut and patch mechanism’?

a.       Photoreactivation
b.      Nucleotide excision repair
c.       Base excision repair
d.      Mismatch repair

2. DNA helicase enzyme involved in base excision repair mechanism is______.

a.       DNA helicase I
b.      DNA helicase II
c.       DNA helicase III
d.      DNA helicase IV

3. In mismatch repair mechanism, which of the following protein recognize DNA mismatches in the genomic DNA?

a.       MutH
b.      MutS
c.       MutL
d.      UvrD

4. The main difference between nucleotide excision repair  (NER) and base excision repair (BER) is:

a.       In NER double strand breaks are repaired where as in BER single strand breaks repaired
b.      NER is a light dependent reaction whereas BER is light independent process
c.       In NER phosphodiester backbone is first cleaved where as in BER phosphodiester backbone is cleaved later
d.      All of these

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biological chemistry

Artemisinin: A Wonder Phyto-drug Against Malarial Parasite: Plasmodium falciparum; & Nobel Prize Winning Contribution of Prof. Youyou Tu, China (Nobel Prize 2015: Physiology and Medicine)


Nobel Prize 2015 Physiology and Medicine

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Youyou Tu China Nobel Prize 2015 Physiology and Medicine

source: The Hindu

Artemisinin is an anti-malarial parasite drug extracted from a Chinese medicinal plant called sweet wormwood (Artemisia annua; Asteraceae family). It is also known as qinghaosu in Chinese and it is the most rapid acting drug currently available against the malarial parasite, Plasmodium falciparum.

The 2015 Nobel Prize in Physiology and Medicine is shared by William C. Campbell, Satoshi Omura and Youyou Tu for the discoveries of therapies against parasitic infections which saved millions of life over the globe. Among the three Nobel laureates, Professor Youyou Tu of China shares half of the Prize money for the credit of isolation, purification and structure elucidation of Artemisinin, the anti-malarial parasite drug for the first time from a Chinese traditional medicinal plant Artemisia annua. Professor Tu is the first China based Woman scientist to win the science Nobel.

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