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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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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biological chemistry

Nucleotide Biosynthesis (De-novo & Salvage Synthesis of Purine & Pyrimidine Nucleotides in the Cells)


“The formation of DNA’s structure by Watson and Crick may turn out to be the greatest developments in the field of molecular genetics in recent years”

Linus Pauling, 1953

Purines (Adenine & Guanine) and pyrimidines (Thymine, Cytosine & Uracil) are the two classes of nucleotides which forms the nucleic acids (DNA & RNA) in the cells. Apart from the primary role of DNA and RNA as “genetic information storage”, nucleotides also serves different functions in the cells such as energy carrier (ATP and GTP), components of co-enzymes (NAD and FAD) and cellular signal transduction (cAMP and cGMP as ‘second messengers’). An ample supply of nucleotides in the cell is very essential for all the cellular processes. This post discuss the biosynthesis of Purines and Pyrimidines in an EASY but detailed way.

Pathways for the biosynthesis of nucleotides

Nucleotide biosynthesis in the cell can be grouped into two broad classes. (1) de-novo synthesis and (2) synthesis by salvage pathways.

I. De-novo synthesis (synthesis from scratch): it is a biochemical pathway in which nucleotides are synthesized new from simple precursor molecules.
II. Salvage pathway (recycle pathway): used to recover bases and nucleosides formed during the degradation of RNA and DNA

Biosynthesis of purine & pyrimidine

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mcq biology

NET Life Science Model Question Paper 2015: Biology MCQ-8: Biochemistry: Amino Acids: Part 4


Biochemistry Quizzes


Biology MCQ (Multiple Choice Questions in Life Science)
(Sample/Model/Practice Questions for JRF/NET Life Science Examination, ICMR JRF, DBT JRF, GATE, ICAR NET, PG Entrance)

MCQ Biochemistry: Amino Acids Part 4 (MCQ 008)


1). Which group of a fully protonated glycine (NH3+ – CH2 – COOH) first release a ‘proton’ when it is titrated against – OH- ions?

a.       Carboxyl group
b.      Amino group
c.       Both at the same time
d.      It cannot be predicted

2). pKa is the measure of a group to __________ proton.

a.       Take up
b.      Release
c.       Combine
d.      Consume

3). Which of the following amino acid bears a guanidine group in the side chain?

a.       Lysine
b.      Arginine
c.       Histidine
d.      Proline

4). The precursor of glycine synthesis in microbes and plants is_______.

a.       Serine
b.      Leucine
c.       Valine
d.      None of these

5). Single letter code of selenocysteine is _____.

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mcq biology

MCQ Biology 07: Biochemistry: Amino Acids – Part 3 for Life Science JRF/NET Examination, June 2015


Biochemistry Quizzes

Biology MCQ (Multiple Choice Questions in Life Science)
(Sample/Model/Practice Questions for JRF/NET Life Science Examination, ICMR JRF, DBT JRF, GATE, ICAR NET, PG Entrance)


Biochemistry: Amino Acids Part 3 (MCQ 007)


(1). pH below pI amino acids will be___.        (ICMR JRF Exam, 2006)

a.       Anionic
b.      Cationic
c.       Net charge zero
d.      No charge

(2). Naturally occurring proteins are usually polymers of _____.

a.       D-amino acids
b.      L-amino acids
c.       A mixture of D and L amino acids
d.      Either D amino acids or L- amino acids

(3). At zwitterionic form, an amino acid will act as_____.

a.       Proton donor
b.      Proton acceptor
c.       Proton donor and acceptor
d.      None of these

(4). Which of the following amino acid is more likely to occupy the interior of a globular protein?

a.       Methionine
b.      Aspartate
c.       Lysine
d.      Arginine
e.       All of these

(5). Proteins absorb UV light at 280 nm and show a characteristic peak at this wavelength. Which amino acid residue in the protein is responsible for this absorption?

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