BIOCHEM EXAM 3 MCQS (ICS/SDL/BRS) QUESTIONS AND ANSWERS WITH COMPLETE SOLUTIONS VERIFIED
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BIOCHEM EXAM 3 MCQS (ICS/SDL/BRS) QUESTIONS AND ANSWERS WITH COMPLETE SOLUTIONS VERIFIED
E. Has a cyclic structure, distinct R group is least likely to have an error. If the R group is distant or unique it is least likely to pick up a different amino acid.
Which amino acid is least likely to ha...
BIOCHEM EXAM 3 MCQS (ICS/SDL/BRS) QUESTIONS AND
ANSWERS WITH COMPLETE SOLUTIONS VERIFIED
E. Has a cyclic structure, distinct R group is least likely to have an error. If the R
group is distant or unique it is least likely to pick up a different amino acid.
Which amino acid is least likely to have an error made by its corresponding aminoacyl
tRNA synthetase?
A. Isoleucine tRNA synthetase is slightly larger than Valine tRNA synthetse. It is
more likely to mistakenly put valine in place of isoleucine, it requires
proofreading (editing).
The diagram shows the synthesis site for two aminoacyl tRNA synthetases. Which
aminoacyl tRNA synthetase will need the editing site?
D. Contain the largest fraction of cellular RNA.
Yes, rRNA has the largest fraction of cellular RNA, the RNA found in the cell as a
whole compared to tRNA and mRNA.
A. Need chaperones to fold properly. No ribosomes done need chaperones,
chaperones are needed for the proteins produed to fold them collectly.
B. Are free or bound (to ER) but do not exchange. No, Ribosomes ARE free or
bound but they DO exchange.
C. Subunits are covalently linked. No, ribosomes are bounded by ionic and
hydrogen bonds which are easy to break and dissociate. Ribosomes needs to be
dissociated by the end of translation.
Ribosomes:
A. Need chaperones to fold properly.
B. Are free or bound (to ER) but do not exchange.
C. Subunits are covalently linked.
D. Contain the largest fraction of cellular RNA.
,B. Two large rRNAs, one small rRNA, approximately 50 proteins.
30s is composed of 16s, which is a >15s so its a large rRNA. 50s is composed of
23s, which is >15s so its a large rRNA, and 5s which is <15s so its a small rRNA.
Which statement accurately describes the composition of the ribosomes? Note, large
RNA >15s, small RNA <15s in prokaryotes.
A. Several small rRNAs, one large rRNA, about 10 proteins.
B. Two large rRNAs, one small rRNA, approximately 50 proteins.
C. Three small rRNAs, one large rRNA, over 50 proteins.
D. Over 50 small rRNAs, 3 large proteins
E. Three tRNAs, two rRNAs, about 10 proteins.
B. To allow covalent addition to the tRNA. Yes, this is the PRIMARY purpose of
activation.
A. To allow the peptide bond to form in the ribosome.
C. To allow tRNA synthetase to recognize the correct amino acid. No, its is true
but not the primary purpose of activation.
D. To allow fidelity in codon: anticodon recognition. No, this the contribution of
Elgonatinon.
What is the purpose of activation of the amino acid in protein synthesis?
A. To allow the peptide bond to form in the ribosome.
B. To allow covalent addition to the tRNA.
C. To allow tRNA synthetase to recognize the correct amino acid.
D. To allow fidelity in codon: anticodon recognition.
E. The whole tRNA. Yes, the entire tRNA is being recognized, its size, shape, and
charge. It is the ENTIRE TERTIARY STRUCTURE, including its loops and stems,
contributes to the recognition by aminoacyl-tRNA synthetase.
A. Anticodon loop only. True, but not BEST answer. The anticodon loop is where
there is correct pairing. It ensures the recognition of the correct mRNA codon.
,B. D loop only. True but not BEST answer. D loop contributes to recognition, its
structure helps define the tRNA's shape and other synthetases bind here.
C. Anticodon and D loops. True, but not BEST answer.
D. Anticodon loop and 3' acceptor stem. True, but not BEST answer. The anticdon
loop is where there is correct pairing and 3' acceptor stem is where the amino
acid binds.
How can the tRNA be recognized by the aminoacyl tRNA Synthetase (aaRSs)?
A. Anticodon loop only
B. D loop only
C. Anticodon and D loops
D. Anticodon loop and 3' acceptor stem.
E. The whole tRNA
E. Coupling of transcription and translation.
Prokaryotic cells dont have a nucleus, tRNA happens in the nuclues in the
eukaryotic cells. In eukaryotic cells, there is separation in time and place,
translation cannot start in eukaryotes unless transcritipn is completely over. In
prokaryotic cells, the ribosomes are readily accessible so you dont need to finish
transcription beofre translation starts, transcription and translation are coupled.
Other major differences:
—In prokaryotes there are only 3 IF's, but in eukaryotes there are 12 IFs, thus its
more complicated.
-In prokaryotes there is Shine Delgaro Sequence, unique in prokaryotic cells and
relies completely on the first nucleotide sequence in the mRNA to recognize the
first AA to be added.
A. Initiation requires separation of large and small subunits. Similarity.
B. Use of AUG as a start codon. Similarity
C. Ribosome has three tRNA docking sites. Sim
, Which is different between eukaryotic and prokaryotic translation?
A. Initiation requires separation of large and small subunits.
B. Use of AUG as a start codon.
C. Ribosome has three tRNA docking sites.
D. Use of unique/special tRNA for the first codon.
E. Coupling of transcription and translation.
C. Use of rRNA to recognize start 5'—end of mRNA. Yes, this answer is about the
Shine Delgarno Sequence of the prokaryotic cell. The SDS will recongize the 30s
of the rRNA, cloer to the 5'—end. Ensuring when the first sequence comes in it
starts at the AUG initiation codon.
A. Presence of multiple ribosomes on each message (polysome). Similarity.
B. Translation occurs in the cytoplasm. Similarity.
C. Use of rRNA to recognize start 5'—end of mRNA. Difference, this is in
prokaryotes only.
D. Termination codons are recognized by proteins. Similarity, those proteins are
called releasing factors (RFs).
E. Translocation of tRNA (with peptide) from A to P site requires GTP. Similarity.
Which is different between eukaryotic and prokaryotic translation?
A. Presence of multiple ribosomes on each message (polysome).
B. Translation occurs in the cytoplasm.
C. Use of rRNA to recognize start 5'—end of mRNA.
D. Termination codons are recognized by proteins.
E. Translocation of tRNA (with peptide) from A to P site requires GTP.
B. IF2 (bings initiator tRNA to P site). Yes, bind to the GTP, break the GTP to
attach a phosphate. IF2 is a GTP—binding protein, this is uniqe to prokaryotic
cells.
A. IF1 (separates large/small subunits).
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