Download third of Chapter 10: Translation

Chapter 10
Translation
(pp. 417-435)
Jones and Bartlett Publishers © 2005
Translation overview
• Components of translation
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mRNA
Ribosomes (30S+50S, 40S+60S)
tRNA
aminoacyl tRNA synthetases
initiation, elongation, and release factors
Nonsense-mediated decay
• What happens if an intron was not spliced out?
Nonsense-mediated decay
• What happens if an intron was not spliced out?
• Premature chain-termination codons could be in
the intron, so some of the transport proteins at
exon-exon junctions would remain.
• If these proteins remain on the mRNA, nucleases
will degrade the defective mRNA.
• Otherwise, the good mRNA molecules will be
cleaned of the proteins and can be used for
multiple translation cycles.
Protein synthesis in an eukaryotic cell is initiated by assembly of an
initiation complex (at the 5’-end of the mRNA) which slides
downstream till it finds an initiation codon (AUG)
Protein synthesis occurs on ribosomes with the
help of a large number of protein factors
Steps in the elongation stage of protein synthesis
Steps in the termination of protein synthesis
The E. coli ribosome during
translation
Three-dimensional structure of a
monomeric protein
Alternative pathways in protein folding
Prokaryotic ribosomes can start protein synthesis
at internal sites in a mRNA
Coupling of transcription
and translation
Coupling of transcription
and translation
Coupling of
transcription
and
Translation
(ONLY IN
PROKARYOTES!)
 Polyribosome
or polysome
(Cracking the code)
Frameshift mutations
Insertion (or deletion) of a nucleotide in
template DNA (a frameshift mutation) causes
multiple amino acid changes
The standard genetic code
Wobble Rule
RNA molecules with repeating sequences lead to
proteins with only a few repeated amino acids
The standard genetic code
The cloverleaf model and the 3-dimensional
structure of a tRNA molecule
Inosine
In
tRNA
Codon Usage
Nonsense (chain termination) mutants can be
suppressed by a mutant tRNA capable of
recognizing the termination codon as a sense codon