6 Protein Synthesis Flashcards Preview

Biochemistry > 6 Protein Synthesis > Flashcards

Flashcards in 6 Protein Synthesis Deck (38):

what are the sizes of the two general subunits of ribosomes?

40 and 60S


60S ribosomes are compsed of what size subunits?

5, 5.8, and 28S


40S ribosomes are composed of subunits of what size?



what is a 3 and 5' UTR and where are they found

-regions of the transcript that are not translated into protein
-one is found on the 3' end of the 5' 7methyl guanosine cap and the other on the 5' end of the 3' polya tail


what does it men that codons are degenrate sequences?

there are several different codons for one particular aa


what is the universal acceptor sequence for tRNA?



name two post transcriptional modifications made to tRNA?

-addition of CCA sequences on the 3'-terminal
-modification of bases at specific positions to produce unusual bases


before an aa is incorporated into a protein chain, how does it interact with tRNA?

it is attached by its carboxyl end to the 3' of the appropriate tRNA


what purpose does the aa associating with tRNA serve?

-by associating with the correct tRNA with the correct anticodon, it ensure correct placement in the protein
-association with tRNA creates a high energy bond at the carboxyl end which is used for attachment to the protein


T/F there is one synthetase for all amino acids

-there is a different one for every amino acid


does ATP interact with tRNA or the aa before the aa associates with tRNA? what facilitates this reaction?

the aa, forming aminoacyl-AMP
-aminoacyl-tRNA synthetase


what is the purpose of the anticodon?

so the tRNA binds to the correct codon to incorporate the correct amino acid


what is the wobble hypothesis? why is this important?

more relaxed bonding takes place between the 3' base of the codon and the 5' base of the anticodon. important so that the third base of the anticodon can associate with a number of different bases


what explains why there are fewer tRNA's than codons?

the wobble hypothesis


what is the first ribosomal subunit to associate with the transcript? and where? what other factor is with it?

40S at the 5' cap, it then moves down to the start codon (AUG)
-eIF2-GTP-Met-tRNA (which leaves once at the start codon)


to initiate translation, what does Met-tRNA bind to?

eIF2 and GTP


what does the Met-tRNA-eIF2-GTP complex bind to before translation?

40S ribosome, making the 40S complex


in which direction along the mRNA does translation take place?

5' to 3'


what is the initiation codon that the Met-TRNA-eIF2-GTP complex are looking for?



once the initiation codon is found by the 40S complex, what happens?

-eIF2 is released, permitting the addition of the 60S subunit


what are the three sites on a ribosome and what are their function?

A = accomodates the incoming aminoacyl-tRNA
P = peptidyl-tRNA complex (the tRNA still linked to all the amino acids added to the cahin so far
E = exit site is for empty tRNA that has donated its aa


what are elongation factors necessary for?

position subsequent aminoacyl-tRNA's on the ribosome


what is the role of eEF1a? how does it perform this function?

It is responsible helping to load the new aa-tRNA onto the A site of the ribosome. It dows this using GTP as an energy source


how is GTP loaded onto eEF1a?

after GTP is used to bind the aa-tRNA to the A site, eEF1b binds to eEF1a, kicking off GDP. This allows for a new GTP molecules to come along and bind to eEF1a, kicking off eEF1b


what group of proteins regullates the fidelity and rate of protein elongation?

EF1 by catalyzing the GTP-dependent binding of aa-tRNA to ribosomes


what is the role of eEF2?

-necessary for translocation: after the new peptide bond is formed, the ribosome must be moved in the 3' direction to open up the A site to a new aa-tRNA
-this is a GTP dependent process


what is peptidyl transferase a component of?

28S ribosome


what are the three triplets that function as termination signals?



what binds to the stop codon?

termination factor, ending translation


walk through the step of prokaryotic translation termination

-peptidyl-tRNA bound to the P site
-stop codon is exposed at the A site
-RF1 (or RF2) recognizes the stop codon
-RF3 promotes the hydrolysis of the ester bond between the polypeptide and the tRNA at the P site


what is a big difference between eukaryotic and prokaryotic mRNA's?

most human mRNA's are monocystronic and most prokaryotic mRNA is translated many times with several ribosomes attached simultaneously


missense mutations can activate what?

cryptic splice sites (changes the splicing pattern of exons/introns)


what is a nonsense mutation?

when a mutation leads to a premature stop codon


what is a missense mutation?

when a single nucleotide change causes the codon to code for a different amino acid


what causes a frame shift mutation?

an insertion or deletion


when does phosphorylation of eIF2 occur and what is the effect?

in times of stress such as aa starvation, dsRNa, or unfolded proteins. Leads to inactivation of eIF2


what are internal ribosome entry sites?

special sequences used by viruses to recruit the pre-initiation complex in a manner that does not involves the Cap or initial scanning process


what are miRNA's and what are their role?

about 21 nt long, noncoding and usually target the 3'UTR of mRNA. They recruit the RISC complex and either prolong tranlation or destroy the transcript
-play an important role in regulation of translation