The Nobel Prize in Physiology or Medicine 2006
Andrew Z. Fire, Craig C. Mello
Photo: L. Cicero
Photo: J. Mottern
Andrew Z. Fire
Craig C. Mello
The Nobel Prize in Physiology or Medicine 2006 was awarded jointly to Andrew Z. Fire and Craig C. Mello "for their discovery of RNA interference
| Andrew Zachary Fire | |
|---|---|
 | |
| Born | April 27, 1959 Palo Alto, California |
| Residence | Stanford, California |
| Nationality | American |
| Fields | Biologist |
| Institutions | Johns Hopkins University Stanford University |
| Alma mater | University of California, Berkeley Massachusetts Institute of Technology |
| Doctoral advisor | Phillip Allen Sharp |
| Known for | RNA interference |
| Notable awards | Nobel Prize in Physiology or Medicine (2006) |
Small interfering RNA (siRNA), sometimes known as short interfering RNA or silencing RNA, is a class of double-stranded RNAmolecules, 20-25 nucleotides in length, that play a variety of roles in biology. The most notable role of siRNA is its involvement in the RNA interference (RNAi) pathway, where it interferes with the expression of a specific gene. In addition to its role in the RNAi pathway, siRNA also acts in RNAi-related pathways, e.g., as an antiviral mechanism or in shaping the chromatin structure of a genome; the complexity of these pathways is only now being elucidated.
siRNAs were first discovered by David Baulcombe's group at the Sainsbury Laboratory in Norwich, England, as part of post-transcriptional gene silencing (PTGS) in plants. The group published their findings in Science in a 1999 paper titled "A species of small antisense RNA in posttranscriptional gene silencing in plants".[1] Shortly thereafter, in 2001, synthetic siRNAs were shown to be able to induce RNAi in mammalian cells by Thomas Tuschl, and colleagues in a paper published in Nature.[2] This discovery led to a surge in interest in harnessing RNAi for biomedical research and drug development.
RNA is an acronym for ribonucleic acid, a nucleic acid. Many different kinds are now known.[1]
The main function of RNA is to carry information of amino acid sequence from the genes to where proteins are assembled on ribosomes in the cytoplasm. This is done by messenger RNA (mRNA). The sequence of base pairs is transcribed from DNA by an enzyme called RNA polymerase and is reformed in the mRNA. Then the mRNA moves from the nucleus to the ribosomes in the cytoplasm to form proteins. The mRNA translates the sequence of base pairs into a sequence of amino acids to form proteins. This process is called translation.
RNA is physically different to DNA: DNA contains two intercoiled strands whereas mRNA only contains one single strand. RNA also contains different bases to DNA. It contains:
(A) Adenine (G) Guanine (C) Cytosine (U) Uracil
The first three bases are also found in DNA, but Uracil replaces Thymine as a complement to Adenine.
RNA also contains ribose as opposed to deoxyribose found in DNA. These differences result in RNA being chemically more reactive than DNA. This makes it the more suitable molecule to take part in cell reactions.
RNA is the carrier of genetic information in certain viruses, especially the retroviruses like the HIV virus. This is the only exception to the general rule that DNA is the hereditary substance.
Types of RNA.
Non-coding RNAs
Two kinds of non-coding RNAs help in the process of building proteins in the cell. They transfer RNA (tRNA) and ribosomal RNA (rRNA).
[change]tRNA
Transfer RNA (tRNA) is a short molecule of about 80 nucleotides which carries a specific amino acid to the polypeptide chain at a ribosome. Each one (there is a different tRNA for each amino acid) has a site for the amino acid to attach, and an anti-codon to match the codon on the mRNA. For example, codons UUU or UUC code for the amino acid Phenylalanine.
[change]rRNA
Ribosomal RNA (rRNA) is the catalytic component of the ribosomes. Eukaryotic ribosomes contain four different rRNA molecules: 18S, 5.8S, 28S and 5S rRNA. Three of the rRNA molecules are synthesized in the nucleolus, and one is synthesized elsewhere. In the cytoplasm, ribosomal RNA and protein combine to form a nucleoprotein called a ribosome. The ribosome binds mRNA and carries out protein synthesis. Several ribosomes may be attached to a single mRNA at any time.[2] rRNA is extremely abundant and makes up 80% of the 10 mg/ml RNA found in a typical eukaryoticcytoplasm.[3]
Regulatory RNAs
There are a number of RNAs which regulate genes, that is, they regulate the rate at which genes are transcribed or translated.[4]
[change]miRNA
Micro RNAs (miRNA) act by joining an enzyme and blocking mRNA, or speeding its breakdown. This is called RNA interference.
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