What is Disease Viruses ? Who are they?

What is Disease Viruses ? Who are they?

Humans have known and feared diseases caused by viruses for thousands of years. Among the diseases that viruses cause are influenza, smallpox, infectious hepatitis, yellow fever, polio, rabies, and AIDS, as well as many other diseases not as well known. In addition, viruses have been implicated in some cancers and leukemias. For many autoimmune diseases, such as multiple sclerosis and rheumatoid arthritis, and for diabetes, specific viruses have been found associated with certain cases.

In view of their effects, it is easy to see why the late Sir Peter Medawar, Nobel laureate in Physiology or Medicine, wrote, “A virus is a piece of bad news wrapped in protein.”
Viruses not only cause many human diseases, but also cause major losses in agriculture, forestry, and in the productivity of natural ecosystems.

T7 DNA Polymerase

T7 DNA Polymerase



 The T7 DNA polymerase from T7 bacteriophage has 3’-5’ exonuclease and DNA polymerase activity but lacks 5’-3’ exonuclease domain, which is similar to T4 DNA polymerase. The processivity of this enzyme is quite good that is, the average length of DNA synthesized before the enzyme dissociates from the template, is considerably greater than for other enzymes. Thus, the average length of DNA synthesized by a single molecule of bacteriophage T7 polymerase is much greater than that of DNAs synthesized by other DNA polymerases. The binding and polymerization domain is occupied by the carboxy terminus while the potent 3’-5’exonuclease activity resides on the amino terminus.

The exonuclease activity is completed inactivated by incubating the enzyme with a reducing agent, molecular oxygen, and low concentrations of ferrous ions, for several days. Over 99% of the exonuclease activity is abolished without affecting the polymerization activity by these agents, which cause mutations and site specific modifications. The resulting chemically modified enzyme is marketed under the trade name Sequenase is ideal for determining the sequence of long tracts of DNA by the dideoxy mediated chain termination method. 

Alkaline Phosphatase (AP

 Alkaline Phosphatase (AP)


Alkaline Phosphatase is an important tool in molecular biological processes like cloning. It removes 3’- phosphate groups from a variety of substrates. Although in laboratory, it is used to catalyze the removal of terminal 5’-(P), residues from single stranded or double stranded DNA and RNA. The resulting 5’-OH termini can no longer take part in ligation reactions, thus prevents self religation of vectors, reducing the background of transformed bacterial colonies that carry empty plasmids. This enzyme works optimally at alkaline pH (range of 89 in the presence of low Zn+2 concentrations) and hence derived the name.  Alkaline Phosphatase is isolated from various sources:-

 a) Bacterial Alkaline phosphatase Secreted in monomeric form into the Periplasmic space of E.coli, where it form dimers and gets catalytically activated. It’s a remarkably stable enzyme and is resistant to inactivation by heat and detergent. Thus, bacterial alkaline phosphatase is the most difficult to destroy in the reaction mix.

b) Calf Intestinal Phosphatase  Calf intestinal phosphatase is a dimeric glycoprotein isolated from bovine intestine. This has much more practical significance than bacterial alkaline phosphatase, since it can be readily inactivated from the reaction mixture using proteinase K or by heating at 650C for 30 minutes or 750C for 15 minutes in the presence of 10mM EGTA.

c) Shrimp alkaline phosphatase Extracted from cold water shrimp, can be inactivated readily by heating at 650C for 15 min. 

What is Screening, Genetic Tests and Counseling of Cancer?

What is Screening, Genetic Tests and Counseling of Cancer?

Early diagnosis of cancer greatly increases survival; therefore, regular exams for cancer can help to prevent deaths from cancer. These include mammograms and Pap tests for women, prostate cancer tests for men, colonoscopy exams for colon cancer, and regular physical exams for other types of cancer. Individuals with a strong family history of cancer should consider genetic tests for cancer and cancer risk counseling. The focus of cancer risk counseling is the individual’s personal risk of developing cancer and appropriate actions based on that risk. The discovery of the BRCA1and BRCA2genes associated with early development of breast cancer has allowed women with a family history of early breast cancer to be tested for mutations in these genes. Only five to ten percent of breast cancers show evidence of inheritance. Of these, forty-five percent are associated with a mutation in BRCA1and thirty-five percent with BRCA2. The gene or genes for the remaining twenty percent are not yet known. If the BRCA1 and BRCA2test results are negative, there is no evidence that the woman will have breast cancer because of these mutations. However, she may get breast cancer because of somatic mutations in these or other genes. If the BRCA1 orBRCA2test is positive, other family members may be tested to determine whether the gene was inherited. If other family members are negative, then there is less chance of hereditary risk of this form of cancer, although the individual with the mutation does carry an increased risk of the disease. If the test is positive in other family members, there is an increased hereditary risk for breast cancer in that family. The absence of hereditary risk does not mean that there is no other risk for breast cancer. Decisions based on genetic tests can be very complicated. Individuals must be fully informed about the risks before they can make reasonable decisions. Genetic counselors are trained to help individuals make difficult decisions based on genetic tests. The cumulative risk of breast cancer to age seventy for a woman with a BRCA1mutation is about fifty-seven to eighty-five percent depending on whether she is in a high-risk family. Some women find the fear of cancer so disruptive to their lives that they choose mastectomy to prevent cancer. (This is called prophylactic mastectomy.) Similarly, women with BRCA1have a high lifetime risk of ovarian cancer, causing some of them to choose to have their ovaries removed. While these are difficult decisions, the availability of genetic information provides individuals with information that they can use to make such important medical decisions. A young woman with a strong family history of ovarian cancer might find by genetic testing that she does not have the BRCA1 mutation and should not consider removal of her ovaries.

Yeast Artificial Chromosome (YACs)

Yeast Artificial Chromosome (YACs)

These are linear DNA molecules similar to yeast chromosome. Recombinant YACs are made by ligating large fragments of genomic DNA and then the resultant plasmid is introduced into yeast by transformation. The vector carries selection marker, DNA sequences called as telomere, so that the product can be stabilized inside the yeast cell, an origin of replication called autonomous replication origin, ARS. Large size of DNA can be inserted into YAC vectors, usually between 250kilobases to 400kilobasepairs. Large size of mammalian genomic libraries is also made with approximately 1 megabasepairs of foreign inserts. Insertion of foreign DNA into the cloning site inactivates a mutant expressed in vector DNA and formation of red rather than white colonies by yeast strain is observed. Thus transformants are identified as red colonies, which grow in yeast that is mutant for TRP1 and URA3, which ensure that the cell has received an artificial chromosome and with both the telomeres since it is complimented for both the mutations. And the colony also contains foreign DNA because it is red in color.

What is Isochizomers

What is Isochizomers?

Isochizomers are different Restriction endonucleases having same recognition site. In some cases, they cut identically within their recognition site, but sometime they do not. They have different optimum reaction conditions, stabilities and cost that give us an option of what to purchase. Some Restriction endonucleases recognizes only one sequence but never other, called as Ambiguous Recognition Sequence. Eg. BamH I recognize GGATCC, while Hinf I recognizes a 5bp sequence, with an eligibility of sequence starting with GA and ending with TC and having any base in between GANTC. Some REs recognition site has a site for cleavage by other Restriction Endonuclease. e.g: BamH I site GGATCC have site recognized and cleaved by Sau3A I GATC. Thus all BamH I sites can consequently be cut by Sau3A I.