Can RNA form base pairs? Yes, in many circumstances Some are strictly dsRNA molecules, others are...
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Transcript of Can RNA form base pairs? Yes, in many circumstances Some are strictly dsRNA molecules, others are...
Can RNA form base pairs?
• Yes, in many circumstances
• Some are strictly dsRNA molecules, others are folded back pieces of ssRNA with interactions between antiparallel and complementary residues
• Linked to the origin of life - folded RNA molecules can have enzymic function
• The issue is particularly relevant to new and exciting areas of biology
DNA vs RNA helices
B-DNA A-RNA
Uracil is missing this!
Double stranded viral genomes
• Members of the Reoviridae (eg, Rotaviruses)
Single stranded RNA viral genomes
• Generally have a double stranded (ie, fully base paired) intermediate (for example the Picornaviridae - eg, poliovirus, rhinovirus)
• When in single stranded form there is extensive internal base pairing to generate complex 3D structures that have certain functions (eg, Internal ribosomal entry in picornaviruses)
Cap-dependent
Cap-independent
Stewart & Semler (1997) Sem Virol 8;242
Cap-dependent
Cap-independent
What about ribosomal and transfer RNA?
tRNA (cont.)
tRNA cloverleaf
Ribozymes
• “Hammerhead” RNA structures that catalyse RNA and DNA degradation
• Tom Cech - Nobel prize for his discovery
• Wayne Gerlach et al (CSIRO) - “gene shears” or targeted ribozymes
• RNA base pairing is central to their formation and functioning
Ribozyme structure
RNA interference (RNAi)
• Very hot topic in molecular biology
• Also known as “post-transcriptional gene silencing”
• Discovered in plants, known to also operate in fungi, worms, insects and even mammalian cells (in a modified form - see later)
• Ancient origin - probably confers resistance to some viruses, may also have a role in development
Mechanism of RNAi
RNAi as a research tool
• Rapid generation of “loss-of-function” mutants
• Cannot introduce long dsRNA into mammalian cells as this induces antiviral response
• Short interfering RNA (siRNA) is very effective
• Can be added exogenously or synthesised endogenously
Web sites of interest/acknowledgments
• http://www.tulane.edu/~biochem/nolan/lectures/rna/frames/hambtx.htm and
http://www.tulane.edu/~biochem/nolan/lectures/rna/intro.htm
• http://www.ambion.com/techlib/append/RNAi_mechanism.html
• http://ntri.tamuk.edu/cell/ribosomes.html
• http://stat.tamu.edu/~dnguyen/SUP_review/TutorialFigures.pdf