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Biology Layer A Project
Transcript of Biology Layer A Project
scientists discovered that many, if not most, organisms use RNAi not
just to prevent viral infections,
but to regulate the expression
of their own genes. Scientists
have recently discovered a
new class of RNA molecules
called microRNAs. These
microRNAs are produced
during the early stages
of an organism's development. They bind with matching single-stranded RNA molecules that are involved with protein synthesis. When a microRNA binds to its matching messenger RNA, it forms a double-stranded RNA that is recognized by the RNAi system, which then destroys it. This RNAi mechanism silences the expression of that particular gene. Today, scientists are using the
RNAi mechanism to learn more
about what particular genes do
and how to alter their function.
Determining gene function is a
relatively simple matter of
inserting double-stranded RNA
molecules that have a particular
sequence into cells and observing
the effects after RNAi silences the corresponding gene. Conceivably, this method may one day be used to silence gene mutations that cause human diseases such as Huntington's disease, rheumatoid arthritis, cancer, and many others. By using either the body's own mutations or viral invaders, scientists may develop a new type of drug—for example, one that switches off the genes of a cancer cell and leaves healthy cells unaffected. However, because RNAi's potential effects are so powerful, scientists must first determine that they can control the mechanism so that only the target gene is silenced, and not others. Link for the brief explanation on how scientists discovered RNAI Enzyme dicer serves as a molecular ruler, with a clamp at one end and a cleaver at the other end a set distance away, that produces RNA fragments of an ideal size for gene-silencing. What is Small Interfering RNA? Small interfering RNA (siRNA) are small pieces of double-stranded (ds) RNA, usually about 21 nucleotides long, with 3' overhangs (2 nucleotides) at each end that can be used to "interfere" with the translation of proteins by binding to and promoting the degradation of messenger RNA (mRNA) at specific sequences. The central process of RNAi is the chopping of dsRNA into smaller pieces of a defined length
by the appropriately named enzyme Dicer.
Dicer chops dsRNA into two classes of smaller RNAs — microRNAs (miRNAs) and small
interfering RNAs (siRNAs) — that are around
21-23 nucleotides in length.
siRNAs are thought to be the main
protagonists in RNAi. Dicer delivers these
siRNAs to a group of proteins called the RNA-induced silencing complex (RISC), which uses
the antisense strand of the siRNA to bind to and degrade the corresponding mRNA, resulting in gene silencing. On the molecular level, RNA interference is mediated by a family of ribonucleoprotein complexes called RNA-induced silencing complexes (RISCs), which can be programmed to target virtually any nucleic acid sequence for silencing. RISC can locate target RNAs that has been co-opted by evolution many times to generate a broad spectrum of gene-silencing pathways. And which guides the siRNAs to the target RNA sequence. What is complementary base pairing?
It is the standard arrangement of bases in nucleotides in relation to their opposite pairing, such as thymine being paired with adenine and cytosine paired with guanine. Complementary base pairing will organize the different parts that is important in the process of RNAi. This will pair the appropriate pairs in the process. The first and foremost advantage is that RNAi gives us the ability to specifically target a gene. If the target sequence is carefully chosen, a specific gene or genes can be silenced. RNAi can also be used to achieve varying levels of gene silencing, using the same ihpRNA cons trust in different lines. This allows for selection of lines with varying degrees of gene silencing. In addition to this, the timing and extent of the gene silencing can be controlled, so that genes that are essential will only be silenced at chosen stages of growth or in chosen plant tissues. So, RNAi provides us with a great degree of flexibility in the field of functional genomic. Disadvantage: Unlike in insertional mutagenesis, for the use of RNAi the exact sequence of the target gene is required. Once this sequence information is available, the rest of the process is however relatively fast. Secondly, delivery methods for the dsRNA is a limiting step for the number of species which RNAi based approaches can be used easily. Due to this, improvement and further research into the kinds of vectors that can be used safely and reliably is needed. There have also been some reports that it has been difficult to detect mutants in which there has been subtle changes in gene expression. In plants, marker genes are being developed that will indicate if there has been a change in gene expression Concerns about RNAi process in plant biotechnology It is claimed that no novel protein may be produced by these RNAi influenced crops. However, some novel proteins may be present at low levels, below current detection limits. Even if no novel proteins are produced, food safety is still unknown. Of particular concern is the recent publication12 showing the surprising result that
miRNA produced in plants is resistant to digestion in the gut of animals and can be taken up into the bloodstream of the human body. The miRNA in the study was from rice that had been cooked and eaten by humans. This builds on earlier studies of other
animals who also take up small RNAs from their diets into their bodies. It could affect gene expression in the human body. Genomics and Biotechnology, Agriculture and Agri-Food Canada, Southern Crop Protection and Food Research Centre, 1391 Sandford Street, London, Ontario, Canada N5V 4T3; 2Genomics and Biotechnology, Agriculture and Agri-Food Canada, Saskatoon Research Centre, 107 Science Place, Saskatoon, Saskatchewan, Canada S7N 0X2; and 3Department of Biology University of Saskatchewan, 112 Science Place, Saskatoon, Saskatchewan,Canada S7N 5E2. Received 8 September 2008, accepted 29 December 2008. Since 1996, when biotech crops such as corn and soybeans were first grown commercially, the adoption of plant biotechnology has been rapid.7 In Canada, 65 percent of all corn, 65 percent of soybean acres,8 and 99 percent of all canola acres are herbicide-tolerant or insect-resistant. Vegetable oils have enormous potential as alternatives and replacements for fossil oil in high-value industrial applications. A major research thrust in Canada involves delivering the next generation of industrial oil profiles in the seeds of non-food crucifers. Progress in increasing the range of available fatty acids and improving the chemical homogeneity of Canadian crucifer seed oils are herein reviewed. © 2008 Crown in the Right of Canada. Published by John Wiley & Sons, Ltd
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