|Consider the following kinds of viruses.|
|3. Herpes simplex viruses.|
|4. Adeno-associated viruses.|
|Which of the kinds of viruses given above are used as gene-therapy vectors?|
A) 1, 2 and 4
B) 2, 3 and 4
C) 1 and 3
D) All of these
Correct Answer: D
Solution :[d] Gene Therapy It is the insertion of genes into an individual's cells and tissues to treat a disease, such as a hereditary disease in which a deleterious mutant allele is replaced with a functional one. Retroviruses The genetic material in retroviruses is in the form of RNA molecules, while the genetic material of their hosts is in the form of DNA. When a retrovirus infects a host cell, it will introduce its RNA together with some enzymes, namely reverse transcriptase and integrase, into the cell. This RNA molecule from the retrovirus must produce a DNA copy from its RNA molecule, before it can be integrated into the genetic material of the host cell. The process of producing a DNA copy from an RNA molecule is termed reverse transcription. Herpes Simplex Virus This is a human neurotropic virus. This is mostly examined for gene transfer in the nervous system. The wild type HSV-1 virus is able to infect neurons. Infected neurons are not rejected by the immune system. Though the latent virus is not transcriptionally apparent, it does possess neuron specific promoters that can continue to function normally. Antibodies to HSV-1 are common in humans, however complications due to herpes infection are somewhat rare. Adenoviruses These are viruses that carry their genetic material in the form of double-stranded DNA. They cause respiratory, intestinal and eye infections in humans (especially the common cold). When these viruses infect a host cell, they introduce their DNA molecule into the host. The genetic material of the adenoviruses is not incorporated (transient) into the host cell's genetic material. The DNA molecule is left free in the nucleus of the host cell and the instructions in this extra DNA molecule are transcribed just like any other gene. Adeno-associated Viruses These viruses, from the parvovirus family, are small viruses with a genome of single stranded DNA. The wild type AAV can insert genetic material at a specific site on chromosome 19 with near 100% certainly.
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