Question 1

Some viruses can be crystallized and their structures analyzed. One such virus is yellow mottle virus, which infects beans. This virus has a single-stranded RNA genome containing about 6300 nucleotides. Its capsid is 25-30 nm in diameter and contains 180 identical capsomeres. If the yellow mottle virus begins its infection of a cell by using its genome as mRNA, which of the following would you expect to be able to measure?
A) replication rate
B) transcription rate
C) translation rate
D) accumulation of new ribosomes
E) formation of new transcription factors

Accepted Answer

If the yellow mottle virus begins its infection of a cell by using its genome as mRNA, we would expect to be able to measure its translation rate, as the virus will be using the cell's machinery to translate its RNA into protein. Replication rate relates to DNA replication, which is not relevant in this case since the virus has an RNA genome. Transcription rate and formation of new transcription factors relate to transcription, which is also not relevant in this case since the virus uses its RNA genome directly as mRNA. Lastly, accumulation of new ribosomes is not specific to virus translation and therefore not a relevant measurement in this case.

Question 2

Which of the following occurs in prokaryotes but not in eukaryotes?
A) post-transcriptional splicing
B) concurrent transcription and translation
C) translation in the absence of a ribosome
D) gene regulation

Accepted Answer

Prokaryotes do not have a nucleus to separate transcription and translation, so they occur concurrently in the cytoplasm. In contrast, eukaryotes have a nucleus where transcription occurs before the mRNA is processed, spliced, and transported to the cytoplasm for translation. The other options occur in both prokaryotes and eukaryotes. Post-transcriptional splicing and gene regulation occur in eukaryotes and some prokaryotes, while translation always requires a ribosome in both types of cells.

Question 3

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' bases AC. Which of the following hypotheses describes the most likely result?
A) tRNA will not form a cloverleaf.
B) The amino acid methionine will not become covalently bound.
C) The anticodon will not bind with the mRNA codon.
D) The aminoacyl-tRNA synthetase will not be formed.

Accepted Answer

The 3' end of tRNA molecules contains the CCA sequence that is necessary for the covalent attachment of the amino acid. Without these bases, the amino acid methionine will not become covalently bound to the tRNA and will not be incorporated into a growing polypeptide chain during translation.

Question 4

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 ________.
A) none of the proteins in the cell will contain phenylalanine
B) proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU
C) the cell will compensate for the defect by attaching phenylalanine to tRNAs with lysine-specifying anticodons
D) the ribosome will skip a codon every time a UUU is encountered

Accepted Answer

The mutant bacterial cell will incorporate lysine instead of phenylalanine at amino acid positions specified by the codon UUU, since the defective aminoacyl-tRNA synthetase will attach lysine to tRNAs with the anticodon AAA instead of phenylalanine. This will result in a varied and possibly dysfunctional protein structure and function.

Question 5

Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on specificity in the ________.
A) binding of ribosomes to mRNA
B) shape of the A and P sites of ribosomes
C) binding of the anticodon to a small subunit of the ribosome
D) attachment of amino acids to rRNAs
E) binding of the anticodon to the codon and the attachment of amino acids to tRNAs

Accepted Answer

Accuracy in translation is dependent on the specificity of binding between the anticodon of the tRNA and the codon on the mRNA, as well as the attachment of the correct amino acid to the tRNA. The other options are involved in the process of translation, but not specifically in ensuring accuracy.

Question 6

As scientists were unraveling the mysteries associated with transcription and translation in eukaryotes, they discovered there was not a one-to-one correspondence between the nucleotide sequence of a gene and the base sequence of the mRNA it codes for. They proposed the genes-in-pieces hypothesis. How can the genes-in-pieces hypothesis be explained?
A) Introns are noncoding segments of DNA that are present in the initial transcript, but are removed by splicing.
B) Introns are noncoding segments of DNA that are not read or transcribed by RNA polymerase II.
C) Exons are noncoding segments of DNA that are not read or transcribed by RNA polymerase II.
D) Exons are noncoding segments of DNA that are present in the initial transcript but are removed by splicing.

Accepted Answer

The genes-in-pieces hypothesis explains that eukaryotic genes are composed of both coding segments (exons) and noncoding segments (introns). Introns are transcribed along with exons to form the initial transcript, but then must be removed by splicing. This results in a final mRNA sequence that corresponds only to the exons. Therefore, introns are noncoding segments of DNA that are present in the initial transcript, but are removed by splicing.

Question 7

Which of the following statements is TRUE about protein synthesis in prokaryotes?
A) Extensive RNA processing is required before prokaryotic transcripts can be translated.
B) Translation can begin while transcription is still in progress.
C) Prokaryotic cells have complicated mechanisms for targeting proteins to the appropriate cellular organelles.
D) Translation requires antibiotic activity.
E) Unlike eukaryotes, prokaryotes require no initiation or elongation factors.

Accepted Answer

In prokaryotes, transcription and translation occur simultaneously because the nucleus is not separated from the cytoplasm. This means that translation can begin while transcription is still in progress. Prokaryotes have simpler mechanisms for protein synthesis and do not require extensive RNA processing or elaborate targeting mechanisms. They do require initiation and elongation factors, however, like eukaryotes. Antibiotic activity is not required for protein synthesis in prokaryotes.

Question 8

There are 61 codons that each specify the addition of a specific amino acid, and 3 stop codons for which there is no corresponding amino acid. However, there are only about 40 tRNA molecules, representing 40 anticodons. How is that possible?
A) Only about 40 of the recognized 61 codons are present in mRNA.
B) An anticodon forms hydrogen bonds with the codon; it must match the first two bases of the codon but is less specific with respect to the third base.
C) There are tRNAs that can bind one of two related amino acids.
D) Only 20 of the codons are active-one for each amino acid.

Accepted Answer

The genetic code is redundant, meaning that multiple codons can code for the same amino acid. This is possible because the third base in a codon is less specific and can have some flexibility in pairing with the anticodon of the tRNA. This allows for fewer tRNA molecules to recognize the multiple codons that code for the same amino acid.

Question 9

In comparing DNA replication with RNA transcription in the same eukaryotic cell, only DNA replication ________.
A) uses RNA polymerase
B) makes a new molecule from its 5' end to its 3' end
C) occurs in the nucleus of the cell
D) incorporates the entire template molecule in the product

Accepted Answer

During DNA replication, the entire template molecule is incorporated into the new product, while during RNA transcription, only a portion of the template DNA molecule (the gene of interest) is used to make a new RNA molecule. Additionally, DNA replication occurs in the nucleus of the cell, while RNA transcription can occur in both the nucleus and cytoplasm. Finally, while both processes involve the use of polymerase enzymes, DNA replication uses DNA polymerase, while RNA transcription uses RNA polymerase.

Question 10

Refer to the figure associated with this question. The mRNA is smaller than the length of the DNA that codes for it because ________.
A) the regulatory regions (exons) of the gene are not transcribed
B) post-transcriptional modification removes the introns
C) post-transcriptional modification removes the exons
D) bases are added to the tail of the primary transcript

Accepted Answer

Post-transcriptional modification removes the introns, leaving only the coding regions (exons) in the final mRNA molecule. This is why the mRNA is smaller than the length of the DNA that codes for it.

Question 11

There are 61 mRNA codons that specify an amino acid, but only 45 tRNAs. This is best explained by the fact that ________.
A) some tRNAs have anticodons that recognize 4 or more different codons
B) the rules for base pairing between the third base of a codon and tRNA are flexible
C) many codons are never used, so the tRNAs that recognize them are dispensable
D) the DNA codes for all 61 tRNAs, but some are then destroyed
E) competitive exclusion forces some tRNAs to be destroyed by nucleases

Accepted Answer

The rules for base pairing between the third base of a codon and the tRNA can be flexible, allowing some tRNAs to recognize multiple codons. This is known as wobble base pairing and helps to explain how only 45 tRNAs are needed to decode all 61 mRNA codons.

Question 12

A particular triplet of bases in the coding sequence of DNA is AAA. The anticodon on the tRNA that binds the mRNA codon is ________.
A) TTT
B) UUA
C) UUU
D) AAA

Accepted Answer

The answer of A particular triplet of bases in the...

Question 13

What molecules in the spliceosome catalyze the intron removal reactions?
A) RNA polymerases
B) ribozymes
C) tRNA
D) introns

Accepted Answer

Ribozymes, which are RNA molecules with catalytic activity, are the molecules within the spliceosome that catalyze the intron removal reactions.

Question 14

Codons are three-base sequences that specify the addition of a single amino acid. How do eukaryotic codons and prokaryotic codons compare?
A) Prokaryotic codons usually contain different bases than those of eukaryotes.
B) Prokaryotic codons usually specify different amino acids than those of eukaryotes.
C) The translation of codons is mediated by tRNAs in eukaryotes, but translation requires no intermediate molecules such as tRNAs in prokaryotes.
D) Codons are a nearly universal language among all organisms.

Accepted Answer

Codons are a nearly universal language among all organisms, meaning they are generally shared across both eukaryotic and prokaryotic organisms. While there are some minor variations in codon usage between these groups, the fundamental genetic code is largely the same. Therefore, choices A, B, and C are incorrect.

Question 15

If the sequence in the coding strand of DNA for a particular amino acid is 5'AGT3', then the anticodon on the corresponding tRNA would be ________.
A) 5'ACU3'
B) 5'TCA3'
C) 5'UCA3'
D) 5'AGU3'

Accepted Answer

The anticodon on the corresponding tRNA would be 5'ACU3' because it is complementary to the coding strand of DNA.

Question 16

Ribosomes can attach to prokaryotic messenger RNA ________.
A) once post-transcriptional modification is complete
B) before transcription is complete
C) once replication is complete
D) once the primary transcript has been released from RNA polymerase

Accepted Answer

Ribosomes can attach to prokaryotic messenger RNA before transcription is complete, as transcription and translation can occur simultaneously in prokaryotes due to their lack of a nucleus.

Question 17

Use this model of a eukaryotic transcript to answer the following question(s).
-When the spliceosome binds to the transcript shown above, it can attach ________.
A) to the exons
B) to the 5' UTR
C) to the 3' UTR
D) at certain sites along an intron

Accepted Answer

The spliceosome binds at certain sites along an intron to remove it from the mature mRNA transcript.

Question 18

Suppose that an induced mutation removes most of the 5' end of the 5' UTR of an mRNA. What is most likely to happen?
A) Removal of the 5' UTR will have no effect because the exons are still maintained.
B) Removal of the 5' UTR also removes the 5' cap and the mRNA will quickly degrade.
C) The 3' UTR will duplicate and one copy will replace the 5' end.
D) The first exon will not be read because I1 will now serve as the UTR.

Accepted Answer

The 5' UTR is necessary for the 5' cap to be added to the mRNA, which protects it from degradation by exonucleases. Without the cap, the mRNA is likely to be quickly degraded. The remaining answer choices are not likely outcomes of this mutation.

Question 19

What ensures that the correct amino acid is added during translation?
A) the anticodon of a properly formed aminoacyl tRNA
B) the methyl-guanosine cap of a properly modified mRNA
C) the poly-A tail of a properly modified mRNA
D) the twisting number of a properly supercoiled DNA

Accepted Answer

During translation, the correct amino acid is added to the growing polypeptide chain by the complementary base pairing between the codon on the mRNA and the anticodon of a properly formed aminoacyl tRNA. Each tRNA is specific for one amino acid, and the anticodon recognizes only the codon for that amino acid. Therefore, the anticodon of a properly formed aminoacyl tRNA ensures that the correct amino acid is added during translation. The other options (B, C, and D) are not involved in the process of adding the correct amino acid during translation.

Question 20

There should be a strong positive correlation between the rate of protein synthesis and ________.
A) the quantity of DNA polymerase
B) the quantity of RNA polymerase
C) the size of mRNA
D) the number of ribosomes

Accepted Answer

Ribosomes are responsible for protein synthesis, so the more ribosomes present, the greater the rate of protein synthesis. Therefore, there is a strong positive correlation between the rate of protein synthesis and the number of ribosomes. A, B, and C are not directly related to protein synthesis rates.

Quiz 17: Transcription, Rna Processing, and Translation

Which of the following occurs in prokaryotes but not in eukaryotes?

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' bases AC. Which of the following hypotheses describes the most likely result?

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 ________.

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

Which of the following statements is TRUE about protein synthesis in prokaryotes?

There are 61 codons that each specify the addition of a specific amino acid, and 3 stop codons for which there is no corresponding amino acid. However, there are only about 40 tRNA molecules, representing 40 anticodons. How is that possible?

In comparing DNA replication with RNA transcription in the same eukaryotic cell, only DNA replication ________.

Refer to the figure associated with this question. The mRNA is smaller than the length of the DNA that codes for it because ________.

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

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

What molecules in the spliceosome catalyze the intron removal reactions?

Codons are three-base sequences that specify the addition of a single amino acid. How do eukaryotic codons and prokaryotic codons compare?

If the sequence in the coding strand of DNA for a particular amino acid is 5'AGT3', then the anticodon on the corresponding tRNA would be ________.

Ribosomes can attach to prokaryotic messenger RNA ________.

Use this model of a eukaryotic transcript to answer the following question(s) . -When the spliceosome binds to the transcript shown above, it can attach ________.

Suppose that an induced mutation removes most of the 5' end of the 5' UTR of an mRNA. What is most likely to happen?

What ensures that the correct amino acid is added during translation?

There should be a strong positive correlation between the rate of protein synthesis and ________.