HIV is a complex animal virus
AIDS
The animal virus HIV infects certain key cells of the immune system, destroying the ability of the body to defend itself from cancer and disease.
The HIV infection cycle is typically a lytic cycle, in which the HIV RNA first directs the production of a corresponding DNA, and this DNA then directs the production of progeny virus particles. The Future of HIV Treatment.
Combination therapies and chemokines offer promising avenues of AIDS therapy.
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.
What is Viroids?
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Viroids are tiny, naked molecules of RNA, only a few hundred nucleotides long, that are important infectious disease agents in plants. A recent viroid outbreak killed over ten million coconut palms in the Philippines. It is not clear how viroids cause disease. One clue is that viroid nucleotide sequences resemble the sequences of introns within ribosomal RNA genes. These sequences are capable of catalyzing excision from DNA—perhaps the viroids are catalyzing the destruction of chromosomal integrity.
What is plant vector ?
Plant Vectors
A vector is a circular DNA molecule capable of independent existence and replication within a host cell. In case of plants, Ti and Ri are the two most commonly used plasmids which are used as vectors. Plant cells as such do not possess any endogenous plasmids. But two plasmids called pTi and pRi, are present naturally in the bacteria, Agrobacterium tumefaciens and Agrobacterium rhizogenes, respectively. These plasmids provide a naturally occurring transformation system. A part of the plasmid DNA, called as T-DNA, is transferred into the genomes of most dicot and some monocot plants. pTi stands for tumor inducing plasmid and pRi stands for root inducing plasmid. The infection of Agrobacterium tumefaciens is mediated by transfer of a segment of pTi called as T-DNA into the plant cell. Various bacterial chromosomal genes, such as chvB, exo genes, cell genes, are concerned with the biosynthesis of cell attachment polysaccharides due to which the bacterial cells adhere firmly to the plant cells. While two chromosomal genes are expressed constitutively in bacterial cells that is expressed at all the times inside a cell, which are responsible for virulence associated aspects, Agrobacterium tumefaciens Ti plasmid produces tumor like growth from which roots / shots may sometimes be produced. The infected cells are able to grow in culture on a medium devoid of any growth regulator while uninfected normal plant cells need exogenous auxin or cytokinin. These plasmids also carry genes for IAA (Indole Acetic Acid - auxin) and cytokinin production which is the reason for indefinite growth on a growth regulator free culture medium. When pTi is introduced into Rhizobium trifolii, it gains the ability to produce galls and to utilize opines. The crown gall root cells also synthesize unique nitrogenous compounds called opines, which are not produced by normal plant cells, which are not infected, nor are they utilized. The infected cells use opines as their carbon and nitrogen source. The type of opine produced depends on the bacterial strain. Agrobacterium tunefaciens strain produces either octopine or nopaline which the Agrobacterium rhizogenes produce either agropine or mannopine.
Brief note about Ti plasmid
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Ti plasmid is a large mega plasmid conjugative plasmid of ~200kb. pTi is lost when Agrobacterium is grown above 28oC, such cured bacteria do not induce crown galls that is, they become a virulent. pTi and pRi, although do not share sequence homology but are unique in following respects:- a) They contain some genes, which are located within their T-DNA which has regulatory sequences recognized by plant cells, while their remaining genes have prokaryotic regulatory sequences. As a result, the former are expressed only in plant cells but not in the Agrobacterium, while the latter are only expressed in the bacterium. b) These plasmids naturally transfer a part of their DNA, called as T-DNA, into host plant cells. The T-DNA usually contains following important functional regions.
1. T-DNA contains oncogenes and opine synthesis genes and is transferred into host plant.
2. Vir region which regulates the transfer of T-DNA
3. Opine catabolism genes for utilization of opines.
4. Origin of replication for propagation in Agrobacterium. The T-DNA contains a 24bp direct repeat border sequence and contains the genes necessary for tumor / possess gene for auxin and cytokinin biosynthesis. All the genes present in TDNA have eukaryotic regulatory sequences. As a result, these genes are expressed only in plant cells but never express in Agrobacterium. The vir region mediates the transfer of TDNA into plant genomes and hence is essential for virulence. The genes of vir region are not transferred but induce the transfer of T-DNA. Also, the genes present in T-DNA are not responsible for its transfer, but the 24 bp direct repeat at both the left and right ends of TDNA is essential for the transfer. The exact mechanism of transfer of T-DNA is not known clearly known but is brought by the vir region. The phenols produced by wounded plant tissue initiates the transfer process. The T-DNA is transferred into the plant cells as single stranded DNA, which increases the efficiency of its transformation. But, as soon as it enters into the plant cell, it is immediately converted into a double stranded form. This form integrates at random sites in the host plant genome by a phenomenon called illegitimate recombination, which are due to sequence of homology in short segments of the host DNA. This integration is usually in low copy numbers. Few vectors are derived from pTi (wild type) due to some problems posed by wild type plasmid eg. The presence of oncogenes causes a disorganized growth, their large size and lack of cloning sites within the T-DNA, which are needed for the insertion of DNA segments that has to be cloned.
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.
| Plasmid DNA are red circular one |
