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Can RNA form base pairs? PowerPoint Presentation
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Can RNA form base pairs?

Can RNA form base pairs?

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Can RNA form base pairs?

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  1. 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

  2. DNA vs RNA helices B-DNA A-RNA

  3. Uracil is missing this!

  4. Double stranded viral genomes • Members of the Reoviridae (eg, Rotaviruses)

  5. 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)

  6. Cap-dependent Cap-independent Stewart & Semler (1997) Sem Virol 8;242

  7. Cap-dependent Cap-independent

  8. What about ribosomal and transfer RNA?

  9. tRNA (cont.) tRNA cloverleaf

  10. 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

  11. Ribozyme structure

  12. 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

  13. Mechanism of RNAi

  14. 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

  15. 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