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24 Cards in this Set
- Front
- Back
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describe ribosomes |
prokaryotes: 50S+30S= 70S eukaryotes: 60S+40S= 80S composed of rRNA and proteins catalytic rRNA |
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what are the different types of codon mutations |
nonsense (becomes termination codon) missense (becomes different amino acid) silent (no amino acid change) |
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describe programmed ribosomal frameshift |
ribosome moves 1 nucleotide up or downstream on mRNA, changes reading frame allows different protein from same transcript |
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describe RNA editing |
covalent change in the identity or position of RNA bases after synthesis-- alters codons or makes frameshift cytosine deaminase |
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what are the major steps in protein synthesis
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activation of amino acids (tRNA charging) initiatino (rate limiting) elongation termination and release folding and post-translational processing |
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describe the codon- anticodon relationship |
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describe the wobble hypothesis |
fewer tRNAs than necessary to decode 64 amino acid codons |
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describe aminoacyl-tRNA synthetase |
cytosolic enzymes that charge tRNAs with amino acids usually one aa-tRNA synthetase for each amino acid bonds aa to 3' end of tRNA in a 2 step process fidelity is increased by enzymatic proofreading at multiple steps |
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describe the anatomy of a ribosome |
mRNA moves along cleft between large and small subunit A site- new aminoacyl tRNA enters P site- growing polypeptide peptidyltransferase center E site- exit site |
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describe the initiation step of translation in prokaryotes |
IF1 binds to 30S A site IF3 binds to 30S mRNA binds to 30S subunit shine-dalgarno sequence pairs with rRNA at P site first amino acid is recruited (methionine) IF2 load 50S subunit hydrolyze GDP and release 3 IFs |
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describe translation initiation in eukaryotes |
more complex no shine-dalgarno sequence cap-binding complex binds mRNA 5' cap, recruits 40S subunit scans mRNA until initiation site recruits tRNA met and 60S subunit |
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describe the 'closed loop' |
initiation is enhanced by 5' cap and 3' polyA tail mRNA 5' cap recognized by eIF4E polyA tail bound by cytoplasmic polyA binding protein (Pab1p) eIF4E and Pab1p are linked through eIF4G |
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describe translational elongation |
aminoacylated (charged) tRNA is brought to site A by EF-Tu-GTP codon in A site and anticodon on tRNA are complimentary EF-Tu checks pairing, hyrdolyzes GTP and releases itself EF-Tu GDP is recycled peptide bond is formed (A attacks P) catalyzed by peptidyl transferase in 50S subunit translocation: move one codon down (GTP hydrolysis and EF-G) E site exits, A site empty and ready |
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describe translational termination |
termination codon occupies A site no tRNA recognizes this, eventually release factor binds severs bond and releases polypetide dissociates ribosomal subunits |
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define polysome |
cluster of ribosomes on single mRNA molecule increase translational efficiency |
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describe the coupling of transcription and translation in prokaryotes |
in eukaryotes, transcription in nucleus, translation in cytoplasm in pro, soon as its transcribed it is translated mRNAs are polycistronic (multiple polypeptides per mRNA) and short lived |
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describe puromycin |
premature chain termination (analog of aminoacyl tRNA) cannot translocate which promotes peptide dissociation (pro and eukaryotes) |
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describe tetracyclines |
block A site on 30S subunit, inhibits binding of aminoacyl tRNAs
(prokaryotes) |
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describe erythromycin |
bind 50S subunit, inhibit peptidyl transfer and translocation
(prokaryotes) |
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describe chloramphenicol |
bind 50S subunit and inhibit peptidyl transfer
(prokaryotes) |
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describe cycloheximide |
bind 60S subunit and inhibit peptidyl transfer
(eukaryotes) |
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describe streptomycin |
bind 30S subunit, inhibit initiation and cause misreading of mRNA
(prokaryotes) |
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describe diphtheria toxin |
inactivates eukaryotic eEF2 |
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describe ricin |
inactivates 60S subunit of eukaryotic ribosome |
