Difference between Exonuclease and Endonuclease: Comparison Table

Endonuclease vs Exonuclease

Endonuclease vs Exonuclease
(Similarities and Differences between Endonuclease and Exonuclease Enzyme)

Nucleases are a class of enzyme which hydrolyzes the nucleic acids such as DNA and RNA.  They hydrolyze the phosphodiester backbone which connects individual nucleotides in a polynucleotide. There are two broad categories of nucleases depending upon their site and mode of action on the nucleic acid. They are Endonucleases and Exonucleases.

Endonucleases: Endonucleases cleaves the phosphodiester bond in the polynucleotide from the interior (endo). They hydrolyze the phosphodiester bonds present within a polynucleotide chain.  Some endonucleases are non-specific and they can cut the phosphodiester bond between any nucleotides. A special class of endonucleases, called restriction endonucleases (restriction enzymes), is very specific in their action and they cut at a specific sequence in the polynucleotide chain called the Restriction Site. Restriction endonuclease has immense application in recombinant DNA technology.

Learn more: Applications of Restriction Enzymes

Exonucleases: They are nuclease enzyme which cleaves the nucleotides from the ends. They hydrolyze the phosphodiester bonds present either at 3’ or 5’ end of the polynucleotide chain.

The present post discusses the similarities and differences between endonucleases and exonucleases with a comparison table.

Continue reading

Molecular Biology Tutorials

Tumor Suppressor Gene Rb and its Role in Cell Cycle and Cancer

tumor suppressor gene example

Retinoblastoma Protein (pRb) – A Tumor Suppressor Gene/Protein
(The Importance of pRb in Cell Cycle Regulation and Cancer)

What is Retinoblastoma? What is the cause of Retinoblastoma?

Retinoblastoma or RB is a type of cancer affecting the retina of young individuals. RB occurs in the human population both spontaneously and as a heritable disorder. The genetic reason for the occurrence of RB is associated with a structural aberration of the chromosome. In human, the Rb gene is present on the chromosome 13 at the q-14 region. The loss of this region of due to deletion or mutation causes the retinoblastoma.

The condition of retinoblastoma arises only when both the copies of the Rb gene are lost. In the inherited form of the disease, one parental chromosome carries an alteration in this region. A spontaneous mutation in the retinal cells which results in the inactivation of the other copy of Rb gene can cause the tumor development. Thus, the loss of function of Rb protein due to mutation or deletion is the cause of retinoblastoma.

How Rb acts as a tumor suppressor gene?

A tumor suppressor gene is a gene that prevents the development of cancer. When this gene is mutated and its function is lost forever, there is a very high chance of the cell to enter into a cancerous growth.

Continue reading

Notification of CSIR JRF NET, Life Science Examination

TMC ACTREC JRF Exam Notification 2016 for Ph.D in Life Sciences


TMC ACTREC JRF for Ph.D in Life Sciences, Notification, 2016

Advanced Centre for Treatment, Research and Education in Cancer (ACTREC)

(A Grant-in-Aid Institution of the Department of Atomic Energy, Government of India)

Applications are invited, in the prescribed format, for the award of JUNIOR RESEARCH FELLOWSHIPS (JRF 2016)  for Ph.D. in Life Sciences at Tata Memorial Centre. The Tata Memorial Centre (TMC) is an autonomous Grant-in-aid Institution of the Department of Atomic Energy. The TMC is comprised of the Advanced Centre for Treatment, Research and Education in Cancer (ACTREC) and the Tata Memorial Hospital (TMH). The TMC conducts Ph.D. program in Life Sciences and is affiliated to the Homi Bhabha National Institute (Deemed University).

On-going research at TMC includes basic and translational research in Cancer Biology. Specific research topics include study of cell proliferation, differentiation, apoptosis, metastasis, tumor immunology, molecular imaging, carcinogenesis, stem cell biology, biophysics, structural biology, bioinformatics, proteomics, genomics, genetics, epigenetics.

Qualifications: M.Sc. (Applied Biology / Biochemistry / Bioinformatics / Biophysics / Biotechnology / Botany / Life Sciences / Microbiology/ Molecular Biology / Zoology or related Biological Sciences) / M.Tech. (Bioinformatics/ Biotechnology); M.V.Sc.; M.Pharm. from a recognized University, with ³ 60% aggregate marks. Those awaiting results may also apply. Candidates having done post-graduation course of only 1 year duration are not eligible.

Stipend: Rs. 25000/-+ 30% HRA (if hostel facility is not allotted) per month as applicable. Limited hostel facility is available on the ACTREC campus on first come, first served basis.

Continue reading

Genetics Online Tutorials and Lectures

Sex Determination in Melandrium album (Silene latifolia)

Sex determination in Silene latifolia

The XX -XY Sex Chromosomal Mechanism of Sex Determination in Plants

Majority of the flowering plants are monoecious with male and female reproductive parts are borne on the same flowers or different flowers of same plant. Only about 6% of Angiosperms are dioecious (male and female flowers on separate plants).  The studies of sex determination mechanisms in plants were done only in very few species, such as Coccinia, Asparagus and Melandrium. Melandrium album or Silene latifolia (synonym) is a dioecious model plant in genetics belongs to the Family Caryophyllaceae. The diploid chromosome number of Melandrium album is 24 (n = 12). This post describes the genetic mechanism of sex determination in Melandrium album or Silene latifolia.

Melandrium album shows sex chromosomal sex determination. They have X and Y sex chromosomal constitution similar to Drosophila and Human. However, the mechanism of sex determination is quite different from the usual XX – XY system. In Melandrium album, the AAXX individuals will be females and AAXY individuals will be males. The Y chromosome plays a crucial role in the sex determination of Melandrium album. The Y chromosome contains male determining genes and female suppressing genes, both are necessary for the development and maturation of fertile anthers in the male plants. Since the female individuals are homogametic, (produce only one type of gametes – XX constitution) the segregation of X and Y chromosomes occurs only in the male individuals during meiosis.

Usually plants with AAXY chromosomal constitution are males. Sometimes AAXY individuals will be hermaphrodite (bisexual) or androhermaphrodites (forming both bisexual and male flowers on the same individuals). The formation of bisexual individuals in AAXY individuals may be due to the mutation or deletion of the female suppressing genes on the Y chromosome or due to the change in DNA methylation pattern.

Mechanism of sex determination in Melandrium album:

Continue reading

Genetics Online Tutorials and Lectures

Genic Balance Theory of Sex Determination in Drosophila melanogaster

Sex determination mechanism


What is sex determination?

Living organisms, with a very few exceptions, are differentiated into male and female individuals based on their morphological, physiological and behavioral characteristics. Even though the mechanism greatly varies, the sexes of the individuals are genetically determined. The biological system that determines the development of sexual characteristics in an organism is called sex-determination. There are two different types of sex determination systems, they are:

(1). Chromosomal sex determination

(2). Non–genetic sex determination

In chromosomal sex determination, the individuals will process specialized chromosomes called sex chromosomes. In this case, the presence or absence of a particular sex chromosome or the relative ratio of these sex chromosomes determines the sex of the individuals.

Similar to human beings, Drosophila melanogaster (fruit flies) shows XX female and XY male sex chromosomal constitution. However, the mechanism of sex determination is quite different in Drosophila from human. In humans, the Y chromosome is the actual sex determining chromosome. Invariable to the number of X chromosomes, the presence of a single Y chromosome initiates the development of male sex in human embryos. Thus, in human XX and XY individuals will be always female and male respectively. In human XXY and XXXY individuals are also males because of the presence of Y chromosome.

What is Genic Balance System of Sex Determination?

Continue reading