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Rna interference technology

In Structure and Function of RNA , we described the function of mRNA, rRNA, and tRNA. In addition to these types of RNA, cells also produce several types of small noncoding RNA molecules that are involved in the regulation of gene expression. These include antisense RNA molecules, which are complementary to regions of specific mRNA molecules found in both prokaryotes and eukaryotic cells. Non-coding RNA molecules play a major role in RNA interference (RNAi) , a natural regulatory mechanism by which mRNA molecules are prevented from guiding the synthesis of proteins. RNA interference of specific genes results from the base pairing of short, single-stranded antisense RNA molecules to regions within complementary mRNA molecules, preventing protein synthesis. Cells use RNA interference to protect themselves from viral invasion, which may introduce double-stranded RNA molecules as part of the viral replication process ( [link] ).

A eukaryotic cell transcribes a region of DNA into mrNA. Antisense mRNA then binds to the this mRNA to produce a double stranded region. This region is not translated (which means that ribosomes do not bind to the mRNA to produce proteins).
Cells like the eukaryotic cell shown in this diagram commonly make small antisense RNA molecules with sequences complementary to specific mRNA molecules. When an antisense RNA molecule is bound to an mRNA molecule, the mRNA can no longer be used to direct protein synthesis. (credit: modification of work by Robinson R)

Researchers are currently developing techniques to mimic the natural process of RNA interference as a way to treat viral infections in eukaryotic cells. RNA interference technology involves using small interfering RNAs (siRNAs) or microRNAs (miRNAs) ( [link] ). siRNAs are completely complementary to the mRNA transcript of a specific gene of interest while miRNAs are mostly complementary. These double-stranded RNAs are bound to DICER, an endonuclease that cleaves the RNA into short molecules (approximately 20 nucleotides long). The RNAs are then bound to RNA-induced silencing complex (RISC), a ribonucleoprotein. The siRNA-RISC complex binds to mRNA and cleaves it. For miRNA, only one of the two strands binds to RISC. The miRNA-RISC complex then binds to mRNA, inhibiting translation. If the miRNA is completely complementary to the target gene, then the mRNA can be cleaved. Taken together, these mechanisms are known as gene silencing .

Double stranded RNA can be produced from DNA in the nucleus. Dicer than cuts this dsRNA into either miRNA or siRNA. miRNA is an imperfect match and only one strand is usually incorporated into RISC. This blocks translation but the mRNA is stable. The RISC is stuck on the target. The siRNA has a perfect match and is incorporated into RISC. This triggers mRNA cleavage.
This diagram illustrates the process of using siRNA or miRNA in a eukaryotic cell to silence genes involved in the pathogenesis of various diseases. (credit: modification of work by National Center for Biotechnology Information)

Key concepts and summary

  • The science of genomics allows researchers to study organisms on a holistic level and has many applications of medical relevance.
  • Transcriptomics and proteomics allow researchers to compare gene expression patterns between different cells and shows great promise in better understanding global responses to various conditions.
  • The various –omics technologies complement each other and together provide a more complete picture of an organism’s or microbial community’s ( metagenomics ) state.
  • The analysis required for large data sets produced through genomics, transcriptomics, and proteomics has led to the emergence of bioinformatics .
  • Reporter genes encoding easily observable characteristics are commonly used to track gene expression patterns of genes of unknown function.
  • The use of recombinant DNA technology has revolutionized the pharmaceutical industry, allowing for the rapid production of high-quality recombinant DNA pharmaceuticals used to treat a wide variety of human conditions.
  • RNA interference technology has great promise as a method of treating viral infections by silencing the expression of specific genes

Fill in the blank

The application of genomics to evaluate the effectiveness and safety of drugs on the basis of information from an individual’s genomic sequence is called ____________.

pharmacogenomics or toxicogenomics

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A gene whose expression can be easily visualized and monitored is called a ________.

reporter gene

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True/false

RNA interference does not influence the sequence of genomic DNA.

true

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Short answer

If all cellular proteins are encoded by the cell’s genes, what information does proteomics provide that genomics cannot?

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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