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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.