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| DNA vaccine
What is antisense technology?
Antisense refers to opposing the normal order (“sense”) of the code in DNA. The DNA (deoxyribonucleic acid) in genes directs cells to assemble the proteins which comprise living creatures. The order of bases in DNA corresponds to the ordering of amino acids to form the proteins. To produce protein, the DNA of the genes in cells is first transcribed into a very similar molecule called RNA. RNA can move out of the cell’s nucleus, where the genes have to stay. In the surrounding cytoplasm, proteins are put together according to the RNA’s sequence of bases, matching the DNA instructions. Antisense molecules prevent the protein assembly machinery from seeing the genetic instructions on how to order the amino acids. If scientists make a molecule that complements the sequence of bases in the RNA, it will stick to the RNA. The antisense molecule, bound to RNA, will prevent the RNA from making protein. Just as two complementary pieces of Velcro stick together, hiding their loops, the antisense molecules bind to RNA and hide its instructions. Thus, antisense stops the synthesis of the protein coded for by the targeted RNA. In effect antisense has turned off the specific gene, or DNA, that was coding for that protein
The three-dimensional structure of the original ribozyme, the self-splicing intron of Tetrahymena (13). Green and blue ribbons indicate the path of the RNA backbone in the two major domains of the RNA, and the red star marks the active site.
The making of a DNA vaccine.
. Nucleic acid vaccines are still experimental, and have been applied to a number of viral, bacterial and parasitic models of disease, as well as to several tumour models. DNA vaccines have a number of advantages over conventional vaccines, including the ability to induce a wider range of immune response types. Vaccines are among the greatest achievements of modern medicine – in industrial nations, they have eliminated naturally-occurring cases of smallpox, and nearly eliminated polio, while other diseases, such as typhus, rotavirus, hepatitis A and B and others are well controlled. Conventional vaccines, however, only cover a small number of diseases, and infections that lack effective vaccines kill millions of people every year, with AIDS, hepatitis C and malaria being particularly common. First generation vaccines are whole-organism vaccines – either live and weakened, or killed forms. Live, attenuated vaccines, such as smallpox and polio vaccines, are able to induce killer T-cell (TC or CTL) responses, helper T-cell (TH) responses and antibody immunity. However, there is a small risk that attenuated forms of a pathogen can revert to a dangerous form, and may still be able to cause disease in immunocompromised people (such as those with AIDS). While killed vaccines do not have this risk, they cannot generate specific killer T cell responses, and may not work at all for some diseases. In order to minimise these risks, so-called second generation vaccines were developed. These are subunit vaccines, consisting of defined protein antigens (such as tetanus or diphtheria toxoid) or recombinant protein components (such as the hepatitis B surface antigen). These, too, are able to generate TH and antibody responses, but not killer T cell responses. DNA vaccines are third generation vaccines, and are made up of a small, circular piece of bacterial DNA (called a plasmid) that has been genetically engineered to produce one or two specific proteins (antigens) from a micro-organism. The vaccine DNA is injected into the cells of the body, where the "inner machinery" of the host cells "reads" the DNA and converts it into pathogenic proteins. Because these proteins are recognised as foreign, when they are processed by the host cells and displayed on their...
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