1. Ribozymes: RNA Enzymes
Function
Patrick Young

2. Function Ribozymes The ribosome is a ribozyme
Translates RNA into proteins
Responsible for ribosome structure
Ability to position tRNAs on mRNA
3o structure
Folds to serve as an enzyme
Targets RNA
Metal ions – structural stability and formation at active site
RNA segments
Form covalent bonds
Act as molecular scissors
Catalytic activity
Cleavage
Splicing
Ligation
RNA chains
Main Role of Ribozyme: stabilize the RNA core to catalyze protein synthesis

3. Principal RNAs produced in Cells
Type of RNA
Function
mRNA (messenger RNA)
code for proteins
rRNA (ribosomal RNA)
form the basic structure of the ribosome and catalyze protein synthesis
tRNA (transfer RNA)
central to protein synthesis
snRNA (small nuclear RNA)
Function in a variety of nuclear processes →splicing of pre-mRNA
snoRNA (small nucleolar RNA)
Used to process and chemically modify rRNA
scaRNA (small cajal RNA)
Used to modify snoRNA and snRNA
miRNA (microRNA)
Regulate gene expression typically by blocking translation of selective mRNA
siRNA (small interfering RNA)
Turn off gene expression by directing degradation of selective mRNA and the establishment of compact chromatin structures
Other noncoding RNA
Function in diverse cell processes
→ telomere synthesis, X-chromosome inactivation, and the transport of proteins into the ER
Molecular Biology of the Cell (© Garland Science 2008)

4. Cleaving, Ligating, Splicing
Range of catalytic activities
Activity
Ribozymes
Peptide bond formation in protein synthesis
rRNA
RNA Cleavage, Litagation
self-splicing RNA; RNase P; in vitro selected RNA
DNA Cleavage
self-splicing RNA
RNA splicing
RNA polymerization
in vitro selected RNA

5. Cleaving RNA
Molecular Biology of the Cell (© Garland Science 2008)

6. Self-Cleaving Hydrolysis of a ribozyme’s own phosphodiester bond
Hepatitis Delta Virus (HDV)

7. Self-Ligating Joining together with a bond
The ligation reaction forms a 2’,5’-phosphodiester

8. Self-Splicing Ribozyme built into their own intron and is degraded
Introns and RNase P

9. Self-Splicing

10. Hepatitis Delta Virus
Noncoding RNA - function in diverse cell processes
1,700 nucleotides
70% self-complementarity
Essential in viral replication
the only catalytic RNA known to be required for the viability of a human pathogen
Self-cleaving
active in vitro in the absence of any proteins

11. HDV
Purpose - cleave rolling circle replication products into genome-length units
Fastest naturally occurring catalyst
folded into a double pseudoknot containing five helical stems

12. HDV
Requires low concentrations of divalent cations – play in an important role in folding or catalysis

13. References
Alberts, Bruce, John H. Wilson, and Tim Hunt. Molecular Biology of the Cell. New York: Garland Science, Print.
Doherty, Elizabeth A., and Jennifer A. Doudna. "Ribozyme Structures and Mechanisms." Annual Review: Biophysics and Biomolecular Structure 30 (2001): Print.
Ferre´ -D’Amare, Adrian R. "Crystal Structure of a Hepatitis Delta." Nature, 8 Oct Web. <
Flugel, Rolf M. Chirality and Life a Short Introduction to the Early Phases of Chemical Evolution. Berlin: Springer, Print.
Reyes, Roberto. "Ribozymes: Molecular Scissors for Investigating Genetic Function." MadSciNet: The 24-hour Exploding Laboratory. University of Washington School of Medicine. Web. 16 Nov <
Web. 19 Nov <