RNA silencing refers to the process by which the expression of one or more genes is down regulated or entirely suppressed by small non-coding RNAs. It is also referred to the introduction of an anti-sense RNA molecule on gene expression. RNA silencing is also defined as sequence-specific regulation of gene expression that is triggered by double-stranded RNA (dsRNA). RNA silencing mechanisms are highly conserved in almost all of the eukaryotes. The most common and well-studied example of this is RNA interference (RNAi), in which endogenously expressed microRNA (miRNA) or exogenously derived small interfering RNA (siRNA) induces the degradation of complementary messenger RNA(mRNA). Other classes of small RNA have been identified; including piwi-interacting RNA (piRNA) and its subspecies repeat associated small interfering RNA (rasiRNA). The three primary classes of small RNA have currently been identified, namely: small interfering RNA (siRNA), microRNA (miRNA), and piwi-interacting RNA (piRNA).
Small interfering RNA (siRNAs) acts in the nucleus and the cytoplasm and are involved in RNAi. Whereas, siRNAs come from long dsRNA precursors derived from a variety of single-stranded RNA (ssRNA) precursors, such as sense and antisense RNAs. siRNAs may also come from hairpin RNAs which is derived from inverted repeat regions. siRNAs may also arise enzymatically from non-coding RNA precursors. microRNA (miRNA) act in the cytoplasm and mediate mRNA degradation or the translational arrest. However, some of the plant miRNAs have been shown to act directly to promote DNA methylation. miRNAs come from hairpin precursors generated by the RNaseIII enzymes namely Drosha and Dicer. miRNA and siRNA form either the RNA-induced silencing complex(RISC) ...
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...ay interfere with multiple mRNA species, but each with different efficiencies based on the degree of complementarity. Second, miRNA usually target the 3’ non-coding region of RNA transcripts, whereas most scientists design shRNA constructs for mRNA coding regions. Third, and perhaps most complex, miRNA may be transcribed in clusters. Moreover, these clusters may contain miRNA that are identical, similar, or distinct from those in other clusters. One cluster might interfere with a large group of targets, producing a large change in phenotype. A second cluster, induced by a distinct cue, might control some of the same targets as well as distinct mRNAs, producing a different phenotype. Add to this the possibility that some miRNA may interfere with receptors or transcription factors, which in turn impact multiple pathways and one, have a system of remarkable complexity.
Groups of transcription factor binding sites called enhancers and silencers can turn a gene on/off in specific parts of the body.
Nikitina, E. G., Urazova, L. N., & Stegny, V. N. (2012). MicroRNAs and Human Cancer.Experimental Oncology, 34(1), 2-8. Retrieved from http://archive.nbuv.gov.ua/portal/chem_biol/eol/2012_1/002.pdf
Almost all biology students learn the fundamentals of gene expression, DNA contains information which is transcribed into RNA to create protein. Students however, are not taught of RNA Interference, the biological process where RNA molecules inhibit a gene’s expression, RNAi for short. While RNAi is a fairly new discovery, its use in modern biological research is groundbreaking. RNA Interference works by binding Double-stranded RNA molecules (siRNA) to a complementary messenger RNA. The enzymes Dicer and Slicer then cleave the chemical bonds which hold the messeger RNA in place and prevent it from delivering protein silencing instructions thus, the term, Gene Silencing. This phenomenon was first discovered by Richard Jorgensen in 1990 when he was trying to produce deeper purple colored petunias by introducing more purple pigment genes to the flower. To his surprise, the purple petunia turned completely white and got the opposite of his predicted result. At the time Jorgensen coined this effect, “Cosuppression”. It was not until 1998 that Andrew Fire and Craig, C Mello explained the process of RNAi and discovered its use in Caenorhabditis elegans (C. Elegans). In 2006 Fire and Mello won the Nobel Prize in Physiology or Medicine “for their discover of RNA Interference – gene silencing by double stranded RNA”. They utilized the nematode, C. Elegans due to its whole genome being sequenced. This unique characteristic allows for every gene to be tested
There are 4 main mechanisms of modification and regulation of gene expression; DNA methylation, Chromatin Remodeling (architecture), Histone Modification and RNAi (interference/interactions)
In September 14, 1990, an operation, which is called gene therapy, was performed successfully at the National Institutes of Health in the United States. The operation was only a temporary success because many problems have emerged since then. Gene therapy is a remedy that introduces genes to target cells and replaces defective genes in order to cure the diseases which cannot be cured by traditional medicines. Although gene therapy gives someone who is born with a genetic disease or who suffers cancer a permanent chance of being cured, it is high-risk and sometimes unethical because the failure rate is extremely high and issues like how “good” and “bad” uses of gene therapy can be distinguished still haven’t been answered satisfactorily.
In the past 40 years, scientists have developed and applied genetic engineering to alter the genetic make-up of organisms by manipulating their DNA. Scientists can use restriction enzymes to slice up a piece of DNA from an organism with the characteristics they want and spliced (joint) to a DNA from another organism. DNA that contains pieces from different species is called recombinant DNA, and it now has different genetic material from its original. When this DNA inserted back into the organism, it changes the organism’s trait. This technique is known as gene-splicing (Farndon 19).
“The effect of protein synthesis inhibition on the entry of messenger RNA into the cytoplasm of sea urchin embryos”, Hogan and Gross. J. Cell Biol. 49(3):692-701.
"The aim is to decrease the fear of a brave new world and to encourage people to be more proactive about their health. It [Gene therapy] will help humans become better physically and even mentally and extend human life. It is the future” (Hulbert). Dr. Hulbert, a genetic engineer, couldn’t be anymore right; more time, money, and research needs to be put into gene therapy and genetic engineering, since it can cure certain illness and diseases that are incurable with modern medicine, has fewer side-effects than conventional drugs or surgery, and allows humans to be stronger physically and mentally at birth. Gene therapy or genetic engineering is the development and application of scientific methods, procedures, and technologies that permit direct manipulation of genetic material in order to alter the hereditary traits of a cell, organism, or population (NIH). It essentially means that we can change DNA to make an organism better. Genetic engineering is used with animals and plants every day; for example with genetic...
Over the past few decades, advances in technology have allowed scientists to actively manipulate the genetic sequence of an organism through a process called 'genetic engineering'. Many believe that this is a technique which we should exploit and take full advantage of as, after all, it may be the key to curing many hereditary diseases such as heart disease and cancer. It may very well be the solution to overcoming evolutionary barriers and allow us to breed new species. However, if you consider the unknown consequences we may have to face as a result of our futile experimenting, you would find that messing with a system as intricate as nature for curiosity's sake is hardly justifiable.
As previously stated, there are several ways that these changes can occur, but the ones I will be focusing on are changes occurring to methyl and acetyl groups. The mechanism of heritability in animals is information coded into genes. Genes are wrapped around histones in the nucleus. When methyl groups attach to these histones, it winds the genes tighter, and since the shape is altered, it also alters the protein the gene codes for. Generally speaking, when you add a methyl group onto the histones, or "spool" of the gene, it makes it harder to code that gene’s proteins, just like if you got something stuck in the chain on your bike and tried to pedal it. The more methyl groups that build up, the worse the problem becomes. However, in most of the cases acetylation unwinds some of the histones, activating or reactivating a gene. Scientists are explo...
Distinct characteristics are not only an end result of the DNA sequence but also of the cell’s internal system of expression orchestrated by different proteins and RNAs present at a given time. DNA encodes for many possible characteristics, but different types of RNA aided by specialized proteins sometimes with external signals express the needed genes. Control of gene expression is of vital importance for an eukaryote’s survival such as the ability of switching genes on/off in accordance with the changes in the environment (Campbell and Reece, 2008). Of a cell’s entire genome, only 15% will be expressed, and in multicellular organisms the genes active will vary according to their specialization. (Fletcher, Ivor & Winter, 2007).
Secondly the gene has to be cut from its DNA chain. Controlling this process are many restriction endonucleases (restriction enzymes). Each of these enzymes cut DNA at a different base sequence called a recognition sequence. The recognition sequence is 6 base pairs long. The restriction enzymes PstI cuts DNA horizontally and vertically to produce sticky ends.
A recent field of biology, called epigenetics, is rapidly transforming previous ideas on the impact of genes. The...
Position Paper: Gene Therapy in Humans. Advancements in science and medicine are usually accompanied by a myriad of ethical and moral implications. The fairly recent advancement in genetics, called gene therapy, is no exception to the baggage of polarizing views that come with new technology. Gene therapy is an extremely hot topic in both the scientific world and everyday life. New technology, discoveries, and breakthroughs are rapidly occurring in the field every day.
The myriad mysteries of science can be unraveled by the emerging technologies including Biotechnology. Science has always been my interest and forte thus, the choice of Biotechnology as my academic option was the ideal decision. I had prepared for the highly competitive entrance exam AIET to get admission into the integrated Masters Degree in Biotechnology and Bioinformatics at Dr. D.Y. Patil University and secured 87th all over India rank and was proud to gain admission to this venerated university. The academic curriculum has introduced me to amazing subjects like ‘Microbiology’, ‘Molecular Biology’, ‘Biochemistry’, ‘Genetics’ and ‘Industrial Biotechnology’. Although many seminal biological events have been explained in theory during the past century, the technology to harness their potential for benefiting humankind has only been possible during the past few decades. This is testament to the great improvements in biotechnologies and I am glad to be a part of this grand scientific experience.