05-07-2014, 03:52 AM
Other RNA types
SiRNA – small interfering RNA
Small interfering RNA molecules are another type of short RNA molecules that can silence some genes by targeting them for degradation. SiRNAs were discovered at the end of the 20th century by the group of scientists in England. These newly discovered molecules were similar in length to micro RNA molecules (around 22 nucleotides), and their last two nucleotides (at 3’ end) were found overhanging. The 5’ end of small interfering RNA molecules is phosphorylated, while the 3’ end is hydroxylated.
Small interfering RNAs are produced in the cell by the enzyme dicer which cleaves long double stranded mRNA molecules and short hairpin RNAs (it also cleaves pre-micro RNA molecules into miRNAs). Another way for siRNA to be present in the cell is by introducing it inside using transfection. This is very important since scientists are able to make synthetic small interfering RNA molecules. Now, it is only necessary to make siRNAs complementary to the gene we want to silence (post-translational silencing), and insert it into the cell. This mechanism opens a lot of room for genetic experiments, especially those concerning drugs and confirmation of gene function.
The main difference between siRNA and miRNA is in their way of action. While micro RNAs don’t necessarily bind to the target mRNA with great precision, siRNA binds completely (every nucleotide establishes connection with the binding site on the target mRNA). This is due to the fact that micro RNAs are “universal”, meaning that they can bind to more mRNA molecules, while small interfering RNAs bind only to one mRNA from which they have been expressed. Moreover, micro RNAs only inhibit the translation of target mRNA (which goes to p-bodies where it is either stored or degraded), while small interfering RNA cleave the target mRNA themselves.
Their ability to degrade mRNA gives them additional possible functions related to the RNA interference pathways, like the antiviral mechanism or shaping of the chromatin structure.
SiRNA – small interfering RNA
Small interfering RNA molecules are another type of short RNA molecules that can silence some genes by targeting them for degradation. SiRNAs were discovered at the end of the 20th century by the group of scientists in England. These newly discovered molecules were similar in length to micro RNA molecules (around 22 nucleotides), and their last two nucleotides (at 3’ end) were found overhanging. The 5’ end of small interfering RNA molecules is phosphorylated, while the 3’ end is hydroxylated.
Small interfering RNAs are produced in the cell by the enzyme dicer which cleaves long double stranded mRNA molecules and short hairpin RNAs (it also cleaves pre-micro RNA molecules into miRNAs). Another way for siRNA to be present in the cell is by introducing it inside using transfection. This is very important since scientists are able to make synthetic small interfering RNA molecules. Now, it is only necessary to make siRNAs complementary to the gene we want to silence (post-translational silencing), and insert it into the cell. This mechanism opens a lot of room for genetic experiments, especially those concerning drugs and confirmation of gene function.
The main difference between siRNA and miRNA is in their way of action. While micro RNAs don’t necessarily bind to the target mRNA with great precision, siRNA binds completely (every nucleotide establishes connection with the binding site on the target mRNA). This is due to the fact that micro RNAs are “universal”, meaning that they can bind to more mRNA molecules, while small interfering RNAs bind only to one mRNA from which they have been expressed. Moreover, micro RNAs only inhibit the translation of target mRNA (which goes to p-bodies where it is either stored or degraded), while small interfering RNA cleave the target mRNA themselves.
Their ability to degrade mRNA gives them additional possible functions related to the RNA interference pathways, like the antiviral mechanism or shaping of the chromatin structure.
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