Dec 26, Explanation: Functions of plasmids Gene Therapy Plasmids play an important role in gene therapy. Plasmids have no harmful effects unlike viral vectors.
Related questions How does pcr relate to crime scene investigation? How does pcr differ from dna replication? Question a Question What is the role of the primers in PCR? Small pieces of DNA, such as human DNA, can be attached to appropriate elements, circularized, and then introduced into bacteria, where they are propagated--or in other words, copied--along with the host bacterial chromosome.
These small circles containing the cloned DNA are called plasmids. Each bacterial cell typically produces many copies of a plasmid, in contrast to making only one copy of its own chromosome. The fact that plasmids are smaller and in greater number than the host chromosome make plasmids easier to isolate in pure form, which is why researchers commonly use them for studying DNA in the laboratory. A plasmid is a small double-stranded unit of DNA, usually circular but sometimes linear, that exists independent of the chromosome and is capable of self-replication.
Each plasmid carries only a few genes. Credit: Stanley N Cohen. Connections Stanley Cohen. Plasmids come in many different sizes and are used for many different purposes in biotechnology. They first made their mark in the field of recombinant DNA in the s, being used as a tool to insert genes into bacteria to encourage their production of therapeutic proteins such as human insulin. In more recent years plasmid DNA has begun to be investigated as a therapeutic platform for treating infectious, genetic and acquired diseases.
The plasmid is genetically modified to produce one or two specific proteins from a pathogen and then purified for immunisation. DNA vaccines offer several advantages over traditional vaccines. Firstly, they eliminate the need to inject infectious agents. Secondly, they stimulate both B- and T-cell immune responses. Thirdly, they are more stable in different temperatures so are easier to store and transport. Lastly, they can be manufactured on a large-scale and at low cost.
The development of plasmids as vaccines poses significant challenges. Most DNA vaccines tested in experimental trials have so far evoked too weak an immune response in humans to protect against disease. Positive results, however, were announced in from preliminary clinical trials conducted with a DNA vaccine developed against H5N1 avian flu.
Plasmids are also being explored for the development of DNA vaccines for non-treatable neurological disorders, such as ischemic stroke, Parkinson's disease, Alzheimer's disease and multiple sclerosis.
A preliminary study of DNA vaccination against multiple sclerosis, completed in , indicates the approach could be effective for this disease. Independent strands of DNA were first found in bacterial cells in the late s by researchers investigating how bacteria become resistant to antibiotics and how traits are passed on to offspring by phages viruses of bacteria and DNA structures other than chromosomes.
Various names were applied to these DNA strands during this time, including pangenes, bioblasts, plasmagenes, plastogenes, choncriogenes, cytogenes, proviruses, and episomes. The word 'plasmid' was first coined by Joshua Lederberg in He used it to describe 'any extrachromosomal hereditary element'.
Lederberg first used the term in a paper he published describing some experiments he and his graduate student Norton Zinder conducted on Salmonella bacteria and its virus P During the course of this work they observed that virus particles could somehow pick up bacterial genes and transfer them to another host, a process they called transduction.
Yet, how this phenomenon worked and what lay behind remained poorly understood for many years.
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