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24 Cards in this Set
- Front
- Back
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Describe programmed ribosomal shift
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-event downstream causes backup of translation ribosome and changes ORF by 1 nucleotide so misses first termination codon
-allows 2 or more proteins to be produced from 1 mRNA |
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Describe RNA editing
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-base pair exchange after RNA synthesis so codon that would normally code for an amino acid codes for a stop codon
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List the different parts of tRNA
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-CCA 3' end is amino acid arm (highly exposed to solvent b/c needs to bind aa)
-D arm binds to TC arm -anticodon arm binds to codon on mRNA (highly exposed to solvent b/c needs to bind mRNA) |
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Explain the wobble hypothesis
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-3rd space in ribosome for codon has a lot of space so base specificity in 3rd position of codon is low (conformation flexibility)
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what base in an anticodon can base pair to 3 different bases in the 3rd codon position?
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inosine
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Describe the function mechanism of aminoacyl-tRNA synthetase
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-charge tRNA with right amino acid
-usually only one aa-tRNA synthetase for each amino acid -amino acid coupled to ATP -pyrophosphate released as ATP binds to CCA at 3' end |
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what are the subunits of a bacterial ribosome?
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50s and 30s
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describe the anatomy of the ribosome
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-mRNA read between interface of 2 subunits
-A (aminoacyl) site to recognize new incoming charged tRNA -P (peptidyl) site has tRNA with peptide attached -E (escape) site for tRNA without amino acid or peptie -peptidyl transferase center in large subunit where peptide transferred from tRNA in P site to tRNA in A site |
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Describe translation initiation in prokaryotes
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-IF-1 binds to A site
-IF-3 binds to small 30S -mRNA binds to 30S using Shine Dalgarno seq (upstream of start site) and AUG start site binds to P site on 16S rRNA -IF-2-GTP brings in charged tRNA with fMet to 30S -50S joins 30S -GTP hydrolyzed and IFs fall off -initiation complete |
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Describe translation initiation in eukaryotes
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-5' cap recognized by eIF; scans until finds start site
-3' tail recognized by another cytoplasmic polyA binding protein -cap and tail proteins linked together by eIF4G |
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what is the exception to translation initiation in eukaryotes?
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Internal ribosome entry sites
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Describe translation elongation in prokaryotes
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-charged tRNA brought to A site by EF-Tu-GTP
-EF-Tu checks complementarity of codon:anticodon -hydrolyzes GTP and releases itself if right pairing EF-Ts recycles and reforms EF-Tu-GTP |
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Describe peptide bond formation
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-aa on tRNA in A site attacks amino acid in P site
-peptidyltransferase center in large subunit and catalyzes reaction |
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Describe ribosome translocation
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-hydrolysis of EF-G-GTP to move tRNA in P site to E site
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Describe translational termination
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-RF binds to A site
-peptide has nothing to bind to so falls off -RF signals ribosome to hydrolyze terminal pepitdyl tRNA bond, release polypeptide and tRNA, and dissociation ribosomal subunits |
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What are polysomes?
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ribosomes on single mRNA coupling transcription to translation
-possible in prokaryotes because transcription and translation occur in same space (no compartmentalization) |
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What are 2 methods of nonsense suppression?
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-mutation in tRNA that recognizes stop codon but is actually charged with amino acid
-mutation in termination codon that codes for amino acid |
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what is the function of puromycin?
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-premature chain termination in translation
-analog of tRNA so goes into A site and can still participate in peptidyl transfer, but can't translocate to P site |
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How is tetracycline involved in translocation?
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blocks A site on 30S
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How is chloramphenicol involved in translocation?
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inhibits peptidyl transferase in prokaryotes
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How is cycloheximide involved in translation?
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inhibits peptidyl transferase in eukaryotes
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How is streptomycin involved in translation?
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inhibits initiation and misreading of mRNA in prokaryotes
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How does diphtheria toxin affect translation?
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inactivates eEF2
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How does ricin affect translation?
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inactivates 60S subunit (eukaryotes)
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