Slides for discussion of Essential Cell Biology chapter 7 (the very end)

1. Cell & Molecular
Biology

4. Ribozymes

5. Chapter 7

8. RNA with catalytic activity

9. Self-Splicing RNA

10. Self-splicing intron
of bacterial tRNA
http://www.pdb.org/pdb/101/motm.do?momID=65

11. Self-Cleaving RNA

12. A riboswitch that
becomes a self-
cleaving ribozyme
in the presence of
glucosamine.
http://www.pdb.org/pdb/101/motm.do?momID=130

13. Riboswitch

14. “...regulatory elements
built directly into
a messenger RNA.”
http://www.pdb.org/pdb/101/motm.do?momID=130

15. Guanine riboswitch
http://www.pdb.org/pdb/101/motm.do?momID=130

16. RESEARCH ARTICLE
sequence segments (Fig. 1B). The
RNA-Catalyzed RNA nus of the ligase domain was cov
tached to an RNA primer so that
Polymerization: Accurate and able to catalyze primer extension
selected by virtue of their attachm
primer that they extended.
General RNA-Templated Primer In contrast to the parental
which hybridizes to the template, a
Extension capable of general polymerization
ognize the primer-template compl
Wendy K. Johnston, Peter J. Unrau,* Michael S. Lawrence, relying on sequence-specific in
Margaret E. Glasner, David P. Bartel† Therefore, the template RNA was d
be too short for extensive hybridiz
the ribozyme (Fig. 1B). For the p
The RNA world hypothesis regarding the early evolution of life relies on the bozyme (Fig. 1A), the pairing be
premise that some RNA sequences can catalyze RNA replication. In support of ribozyme and the template also co
this conjecture, we describe here an RNA molecule that catalyzes the type of stem known to be necessary for li
polymerization needed for RNA replication. The ribozyme uses nucleoside tion (16). To restore this stem, a s
triphosphates and the coding information of an RNA template to extend an RNA GGCACCA ( purple RNA in Fig
primer by the successive addition of up to 14 nucleotides—more than a com- introduced to hybridize to the segm
plete turn of an RNA helix. Its polymerization activity is general in terms of the ligase domain that formerly paire
sequence and the length of the primer and template RNAs, provided that the template. Finally, because a mo
3 terminus of the primer pairs with the template. Its polymerization is also mode of primer-template recogni
quite accurate: when primers extended by 11 nucleotides were cloned and require the participation of an
sequenced, 1088 of 1100 sequenced nucleotides matched the template. RNA domain, a 76-nt random-seq
ment was appended to the 3 term
The RNA world hypothesis states that early life join oligonucleotides assembled on a tem- degenerate ligase domain (Fig. 1B
forms lacked protein enzymes and depended plate (10–12). However, the templates that Sequence variants able to rec
instead on enzymes composed of RNA (1). can be copied are limited to those that match primer-template in this new configu
Much of the appeal of this hypothesis comes the oligonucleotide substrates, and it has not then extend the primer with tagged
from the realization that ribozymes would have been possible to include sufficient concentra- were enriched by repeated rounds
been far easier to duplicate than proteinaceous tions of all the oligonucleotide substrates selection and amplification (Table
enzymes (2–5). Whereas coded protein replica- needed for a general copying reaction. More that extended their primer by using

19. Artificial
Ribozymes

20. Table 7-4 Essential Cell Biology (© Garland Science 2010)

21. The RNA World

22. Figure 7-43 Essential Cell Biology (© Garland Science 2010)

23. Figure 7-44 (part 1 of 3) Essential Cell Biology (© Garland Science 2010)

24. Figure 7-44 (part 2 of 3) Essential Cell Biology (© Garland Science 2010)

25. Figure 7-44 (part 3 of 3) Essential Cell Biology (© Garland Science 2010)

26. Figure 7-45 Essential Cell Biology (© Garland Science 2010)

27. Figure 7-42 Essential Cell Biology (© Garland Science 2010)

28. Figure 7-46 Essential Cell Biology (© Garland Science 2010)