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20 Cards in this Set
- Front
- Back
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formation of aminoacyl-tRNA
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synthesized by aminoacyl-tRNA synthetases
specific amino acid is attached to 2' or 3' hydroxyl group of the adenosing at the 3' end of corresponding tRNA 1) amino acid + ATP --> aminoacyl-AMP + PPi 2) aminoacyl adenylate + tRNA-->aminoacyl-tRNA |
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aminoacyl-tRNA synthetases
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combines aminoacyl-tRNA with amino acid
has activation site and editing site |
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2 classes of aminoacyl-tRNA synthetases
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recognize tRNA from different sides
class 1 attaches amino acid to 2' hydroxyl; monomer class 2 attaches amino acid to 3'; dimer |
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inosine
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formed by deamination of adenosine, can base-pair with C, U, or A
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ribosome structure (E. coli)
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large (70S), consists of 2 subunits (50S and 30S)
30S contains 21 proteins, 16S rRNA molecule 50S contains 34 proteins, 23S and 5S rRNA main component is rRNA |
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30S subunit holds ______
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30S: mRNA
E (exit), P (peptidyl), A (aminoacyl) sites |
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which subunit recognizes shine-dalgarno sequence?
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16S
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delivery of aminoacyl tRNA to A site
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elongation factor Tu
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translocation of A site peptidyl-tRNA to P site
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catalyzes by EF-G (G protein)
moves into A site and bumps peptidyl tRNA and mRNA over to P/E sites--catalyzed by hydrolysis of GTP to GDP |
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termination codons
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release factor 1: UAA, UAG
RF2: UAA, UGA |
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differences in elongation and termination between prokaryotic and eukaryotic protein synthesis
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EF-Tu=EF1a
EF-G=EF2 RF1/RF2=eRF1 |
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6 differences between prokaryotic and eukaryotic proteins synthesis
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1) euk ribosomes=larger (80S)
2) euk initiation a.a. is met (Met-tRNAi=initiator tRNA); pro initiation a.a. is fmet 3) euk initiating codon is AUG nearest 5' end of mRNA; pro initiating codon is downstream of shine-dalgarno 4) euk ribosome binds to cap; pro ribosome binds to shine-dalgarno 5) euk mRNA has 1 start site and template is for single protein; pro has multiple start sites and can serve as template for many proteins (polycistronic) 6) protein interactions circularize eukaryotic mRNA (using eIF=eukaryotic initiation factor and PABPI=poly(A)-binding protein |
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proteins destined to be secreted or localized to plasma membranes have
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a signal sequence (usually with basic amino acids then a hydrophobic core) followed by cleavage site
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coat proteins
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COPs--play an important role information of buds that form transport vesicles
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SNAREs
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after transport vesicle has formed and is released, v-SNAREs ("v" for vesicle"; proteins) will bind to t-SNARES ("t" for target) in target membrane
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signal-recognition particle mechanism
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1) protein synthesis begins on free ribosome, but is halted when signal sequence exits ribosome and is bound by SRP
2) SRP-ribosome docks with SRP receptor in ER membrane 3) SRP and SRP receptor hydrolyze bound GTPs, freeing SRP 4) protein synthesis continues through translocon directly into ER |
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allowed pairings at the third base of the codon according to the wobble hypothesis
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C--G
A--U U--A or G G--U or C I--U, C, or A |
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formylation of fMet-tRNA
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tRNAf + Methionine--Met-tRNAf
then transformylase uses formyltetrahydrofolate to formylate the Met-tRNAf (only in prokaryotes) |
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formation of the 70S initiation complex (what do all the initiation factors do)
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1) binding of IF3 to 30S subunit prevents premature binding to the 50S subunit
2) IF1 binds near A site, directing fMet-tRNAf to P site 3) IF2 binds GTP and causes conformational change which allows it to associate with fMET-tRNA 4) complex binds with mRNA (correctly positioned due to 16S bound to shine-dalgarno) and structural changes lead to release of IF1 and IF3 5) IF2 stimulates association of 50S subunit, GTP bound to IF2 is hydrolyzed and IF2 is released |
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2 toxins that inhibit protein synthesis elongation
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diptheria toxin and ricin
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