Transcript Slide 1
Evolution connection: Transcription and translation Learning goals: Students will understand that 1) RNA was likely the first genetic material of life, and 2) the many different functions that RNA is capable of performing in the cell today constitute evidence that life was once based on RNA. For the instructor: This short slide set relates the role of RNA in the processes of transcription and translation to RNA’s evolutionary history and the remnants of the RNA world. To integrate it best, use these slides immediately after you’ve discussed transcription and translation. This slide set could be shortened, if you wish, by cutting slides 3, 4, 7 and 8. Each of the following slides comes with a sample script for the instructor. To review this script, download the PowerPoint file and view the Notes associated with each slide. Evolution Connection slideshows are provided by Understanding Evolution (understandingevolution.org) and are copyright 2011 by The University of California Museum of Paleontology, Berkeley, and the Regents of the University of California. Feel free to use and modify this presentation for educational purposes. Evolution connection: Transcription and translation RNA: Jack-of-all-trades 1) mRNA - carries genetic information Flu virus anatomy Complementary DNA strands RNA strand RNA Evolution connection: Transcription and translation RNA: Jack-of-all-trades 2) Spliceosome – RNA cuts and rejoins a mRNA molecule Evolution connection: Transcription and translation RNA: Jack-of-all-trades 3) Self-splicing – some RNA can splice itself Tetrahymena image from Robinson R (2006) Ciliate Genome Sequence Reveals Unique Features of a Model Eukaryote. PLoS Biol 4(9): e304. doi:10.1371/journal.pbio.0040304 Evolution connection: Transcription and translation RNA: Jack-of-all-trades 4) tRNA – recognizes mRNA codons during the process of translation Evolution connection: Transcription and translation RNA: Jack-of-all-trades 5) rRNA – links amino acids together into a protein chain of amino acids peptide bond forming ribosome (made of rRNA) Ribosome image from the Center for Molecular Biology of RNA at the University of California, Santa Cruz. Evolution connection: Transcription and translation RNA: Jack-of-all-trades 6) Self-replicating – some RNA can copy itself. Evolution connection: Transcription and translation What makes RNA so powerful? • It can fold up • Some of its bases can catalyze chemical reactions • It is highly specific (i.e., complementary) tRNA hammerhead ribozyme RNA base pairing Ribozyme structure comes from Scott, W.G., Finch, J.T., Klug, A. (1995) The crystal structure of an all-RNA hammerhead ribozyme: a proposed mechanism for RNA catalytic cleavage. Cell 81: 991-1002 Evolution connection: Transcription and translation DNA RNA • Carries genetic information Needs help! • Carries genetic information • Catalyzes chemical reactions • Binds to other molecules • Self-replicates Can go it alone! Evolution connection: Transcription and translation Which came first, DNA or proteins? So which came first? Evolution connection: Transcription and translation Which came first, DNA or proteins? Neither. Because it was all RNA ... The RNA world! Evolution connection: Transcription and translation Selection for efficient self-replication: Evolution connection: Transcription and translation Chi, Y., Martick, M., Lares, M., Kim, R., Scott, W. G., and Kim, S. (2008). Capturing hammerhead ribozyme structures in action by modulating general base catalysis. PLoS biology. 6: e234. Lincoln, T. A., and Joyce, G. F. (2009). Self-sustained replication of an RNA enzyme. Science. 323: 1229-1232.