Question 1

Which of the following experimental procedures is most likely to hasten mRNA degradation in a eukaryotic cell?

Accepted Answer

The removal of the 5' cap from mRNA is a known trigger for mRNA degradation in eukaryotic cells. The cap structure is important for mRNA stability and translation initiation, so its removal can quickly lead to degradation. The other options listed either have no direct effect on mRNA degradation or may have more complex and varied effects on gene expression.

Question 2

Which of the following is a function of a signal peptide?

Accepted Answer

Signal peptides are sequences of amino acids that target polypeptides to specific cellular compartments. The function of a signal peptide is to direct the polypeptide chain to the lumen of the endoplasmic reticulum (ER) for processing and folding. This involves translocation across the ER membrane, which is facilitated by the signal peptide. Therefore, option D is the correct answer.

Question 3

During splicing, which molecular component of the spliceosome catalyzes the excision reaction?

Accepted Answer

The spliceosome is composed of RNA and protein components, and it is the RNA component of the spliceosome that catalyzes the excision reaction during splicing. Specifically, the RNA component of the spliceosome known as the ribozyme is responsible for catalyzing the two transesterification reactions that occur during splicing.

Question 4

In an experimental situation, a student researcher inserts an mRNA molecule into a eukaryotic cell after he has removed its 5' cap and poly-A tail. Which of the following would you expect him to find?

Accepted Answer

The 5' cap and poly-A tail are important for protecting the mRNA molecule from exonucleases, which can break down the molecule from both ends. Without these protective structures, the mRNA is more susceptible to degradation by exonucleases. Therefore, we would expect the mRNA to be digested by exonucleases because it is no longer protected at the 5' end. Option A is not correct because the mRNA could still exit the nucleus even if the cap and tail were removed. Option B is unlikely because the absence of the tail does not usually trigger polyadenylation. Option C is incorrect because restriction enzymes do not digest mRNA. Option E is also unlikely because the absence of the cap and tail does not usually slow down translation.

Question 5

Which of the following is the first event to take place in translation in eukaryotes?

Accepted Answer

The first step in translation in eukaryotes involves the small subunit of the ribosome recognizing and attaching to the 5' cap of the mRNA. This is crucial for the initiation of translation, as it positions the ribosome correctly to start reading the mRNA from the correct end.

Question 6

A mutant bacterial cell has a defective aminoacyl-tRNA synthetase that attaches a lysine to tRNAs with the anticodon AAA instead of the normal phenylalanine. The consequence of this for the cell will be that

Accepted Answer

The defective aminoacyl-tRNA synthetase will attach lysine to tRNAs with the AAA anticodon instead of phenylalanine. This means that during translation, when the ribosome encounters the UUU codon, which normally specifies phenylalanine, the lysine-charged tRNA with the AAA anticodon will be inserted instead, resulting in lysine being incorporated into the protein sequence.

Question 7

Suppose that an induced mutation removes most of the 5' end of the 5' UTR. What might result?

Accepted Answer

The 5' UTR includes the 5' cap, which is important for stabilizing the mRNA and promoting translation. Removing most of the 5' UTR would therefore result in the removal of the 5' cap and the mRNA being quickly degraded.

Question 8

When the spliceosome binds to this transcript, where can it attach?

Accepted Answer

The spliceosome binds to specific sites along an intron, called splice sites, to remove the intron and join the exons together.

Question 9

Use the following model of a eukaryotic transcript to answer the next few questions.
5' UTR E1 I1 E2 I2 E3 I3 E4 UTR 3'
-When the spliceosome binds to elements of this structure, where can it attach?

Accepted Answer

The answer of Use the following model of a eukaryotic...

Question 10

An experimenter has altered the 3' end of the tRNA corresponding to the amino acid methionine in such a way as to remove the 3' AC. Which of the following hypotheses describes the most likely result?

Accepted Answer

The 3' AC of the tRNA is necessary for the attachment of the amino acid methionine to the tRNA, through a covalent bond. Therefore, if the 3' AC is altered, methionine will not be covalently bound to the tRNA.

Question 11

Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on specificity in the

Accepted Answer

Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on the bonding of the anticodon to the codon, which ensures that the amino acid carried by the tRNA is correct for the codon being read. Additionally, this process is only effective when the amino acid is attached to the correct tRNA, which is why the attachment of amino acids to tRNAs is also crucial for accuracy in translation.

Question 12

The process of translation, whether in prokaryotes or eukaryotes, requires tRNAs, amino acids, ribosomal subunits, and which of the following?

Accepted Answer

Translation requires polypeptide factors, which are GTP-binding proteins, in addition to other factors. ATP is not used for translation, so option A is incorrect. Polymerases are involved in transcription, not translation, so option C is incorrect. SRP (signal recognition particle) and chaperones are involved in protein targeting and folding, respectively, but not in translation itself, so options D and E are incorrect. Therefore, the correct answer is B.

Question 13

Suppose that exposure to a chemical mutagen results in a change in the sequence that alters the 5' end of intron 1 (I1). What might occur?

Accepted Answer

The alteration at the 5' end of intron 1 could disrupt normal splicing, leading to the inclusion of intron 1 in the mature mRNA.

Question 14

What is the function of GTP in translation?

Accepted Answer

GTP is used by initiation factors to energize the formation of the initiation complex during translation. It helps the small ribosomal subunit bind to the mRNA and identify the start codon, which is necessary for translation to begin.

Question 15

Use the following model of a eukaryotic transcript to answer the next few questions.
5' UTR E1 I1 E2 I2 E3 I3 E4 UTR 3'
-Which components of the previous molecule will also be found in mRNA in the cytosol?

Accepted Answer

The 5' UTR, E1, E2, E3, E4, UTR, and 3' UTR will all be present in the mature mRNA that is exported to the cytosol. The introns (I1, I2, I3) are removed during RNA processing in the nucleus and do not appear in the final mRNA molecule that is exported to the cytosol. Therefore, option C is the best choice as it includes all the components that will be found in the mRNA in the cytosol.

Question 16

Alternative RNA splicing

Accepted Answer

Alternative RNA splicing is a mechanism by which different exons are included or excluded from the final mature mRNA product. This mechanism allows the production of proteins of different sizes and functions from a single pre-mRNA. Therefore, option B is the correct answer. The other options are incorrect because they do not describe the process of alternative RNA splicing accurately.

Question 17

There are 61 mRNA codons that specify an amino acid, but only 45 tRNAs. This is best explained by the fact that

Accepted Answer

The phenomenon described is due to the "wobble" hypothesis, which explains that the base pairing rules between the third base of a codon and the anticodon of tRNA are less stringent, allowing a single tRNA molecule to recognize and bind to more than one codon.

Question 18

When translating secretory or membrane proteins, ribosomes are directed to the ER membrane by

Accepted Answer

Ribosomes are directed to the ER membrane by a signal-recognition particle (SRP) that recognizes and binds to the signal sequence on the nascent polypeptide chain as it emerges from the ribosome. The SRP then brings the ribosome to a receptor protein in the ER membrane, where translation can continue.

Question 19

A particular triplet of bases in the coding sequence of DNA is AAA. The anticodon on the tRNA that binds the mRNA codon is

Accepted Answer

The anticodon on the tRNA that binds the mRNA codon is complementary to the mRNA codon, not the DNA sequence. The mRNA codon for AAA in DNA is UUU, so the tRNA anticodon that pairs with this mRNA codon is AAA's complement, which is UUU.

Question 20

When the ribosome reaches a stop codon on the mRNA, no corresponding tRNA enters the A site. If the translation reaction were to be experimentally stopped at this point, which of the following would you be able to isolate?

Accepted Answer

The answer of When the ribosome reaches a stop codon...

Quiz 14: Gene Expression: From Gene to Protein