Traduccin (sntesis de protenas)&

Cdigo Gentico

Jorge Arvalo

2014

Estructura del ribosoma

Figure 27.13: Components of a 70S prokaryotic ribosome.

Figure 27.19: Assembly map for the 30S subunit.

Adapted from A. Spirin, Ribosome Structure and Protein Biosynthesis (Redwood City, Calif.: Benjamin/Cummings, 1986). 1986 Benjamin/Cummings Publishing Company.

Figure 27.16: Low-resolution models of the small and large ribosomal subunits and their 70S complex, as deduced from early electron microscopy studies.

Courtesy of M. Oaks, A. Scheirman, T. Atha, G. Shankweiler, and J. A. Lake, The Ribosome, W. E. Hill, A. Dahlberg, R. A. Garret, P. B. Moore, D. Schlessinger, and J. R. Warner, eds.,p. 181 (New York:American Society of Microbiology Press, 1990).

Figure 27.18: A model of the large ribosomal subunit at 0.9 nm resolution, as determined by x-ray diffraction from crystals.

Provided by N. Ban, P. Nissen, P. Moore, and T. A. Steitz from N. Ban et al., Cell (1998) 93:1105-1115. Cell Press.

Estructura del tRNA

Funcin citoplasmtica del tRNA (aminoacilacin)

Etapas de la traduccin

Figure 27.25: A schematic view of functional regions of the ribosome.

La actividad cataltica peptidil transferasa esta en el 23S rRNA

Regin Peptidil Transferasa conservada

P Nissen et al. Science 2000;289:920-930

Published by AAAS

Mecanismo propuesto de formacion de enlace peptdico por el 23S

rRNA

A proposed mechanism of peptide synthesis catalyzed by the ribosome. A2486 (A2451) is shown as the standard tautomer in all steps, but could be represented as the imino tautomer, which would have a negative unprotonated N3 and a neutral protonated N3. We expect that the electronic distribution is actually between these two extremes. (A) The N3 of A2486 abstracts a proton from the NH2 group as the latter attacks the carbonyl carbon of the peptidyl-tRNA. (B) A protonated N3 stabilizes the tetrahedral carbon intermediate by hydrogen bonding to the oxyanion. (C) The proton is transferred from the N3 to the peptidyl tRNA 3 OH as the newly formed peptide deacylates. Among the variations on this mechanism that should be considered would be a protonated A2486 stabilizing the intermediate, as in (B), with less contribution on acid-base catalysis, as shown in (A) and (C).

Figure 27.28: Some antibiotics that act by interfering with protein biosynthesis.

Inhibe la union de aminoacil-tRNA al ribosoma

Inhibe la actividad peptidil

transferasa del ribosoma

Interfiere la interaccion anticodon-codon.

EL CODIGO GENETICO

El descubrimiento del cdigo gentico

El cdigo gentico es universal

El cdigo gentico es degenerado

El cdigo gentico refleja la existencia de la presin de seleccin

La diversidad de codificacin del genoma es incrementada por las

opciones de franja de lectura

Mutaciones sin sentido (nonsense) y mutantes supresoras

Figure 27.27: How an intergenic suppression mutation can overcome a nonsense mutation.