Deck 13: Genes and How They Work

Question 1

Eukaryotic and prokaryotic organisms differ in how they process genetic information. Which statements best explain one of these differences?

A) In prokaryotes, translation of the mRNA begins before transcription is complete. In eukaryotes, transcription and modification of the mRNA is completed before translation begins.
B) In prokaryotes, genes are transcribed directly into polypeptides. In eukaryotes, genes are transcribed into RNA which is used to assemble polypeptides.
C) In prokaryotes, translation occurs before genes are transcribed into mRNA. In eukaryotes, genes are transcribed into mRNA which is then translated into polypeptides.
D) In prokaryotes, introns are removed before genes are transcribed into mRNA. In eukaryotes, introns are removed after genes are transcribed into mRNA.

Answer 1

In prokaryotes, translation of the mRNA begins before transcription is complete. In eukaryotes, transcription and modification of the mRNA is completed before translation begins.

Question 2

Why are there fewer tRNA anticodons than the 61 needed to match each mRNA codon that codes for an amino acid?

A) There is some flexibility in pairing between the 5' base of the codon and the 3' base of the anticodon.
B) There is some flexibility in pairing between the middle base of the codon and the middle base of the anticodon.
C) There is some flexibility in pairing between the 3' base of the codon and the 5' base of the anticodon.
D) There is some flexibility in pairing between all 3 bases of the codon and all 3 bases of the anticodon.

Answer 2

There is some flexibility in pairing between the 3' base of the codon and the 5' base of the anticodon.

Question 3

What happens during RNA splicing in eukaryotes?

A) The product of translation, called the primary transcript, is cut and some pieces are joined back together to form the mature mRNA.
B) The product of transcription, called the primary transcript, is cut and some pieces are joined back together to form the mature tRNA.
C) The product of transcription, called the secondary transcript, is cut and some pieces are joined back together to form the mature mRNA.
D) The product of transcription, called the primary transcript, is cut and some pieces are joined back together to form the mature mRNA.
E) The product of transcription, called the primary transcript, is cut and all pieces are joined back together to form the mature mRNA.

Answer 3

The product of transcription, called the primary transcript, is cut and some pieces are joined back together to form the mature mRNA.

Question 4

Two 6-base sequences are present in bacterial promoters: TATAAT (located 10 nt upstream from the start site) and TTGACA (located 35 nt upstream from the start site). What is the significance of the fact that these two base sequences are different?

A) Binding sites for both the holoenzyme and ATP are provided.
B) Both the location of the start site and the direction of transcription can be established.
C) Binding sites for both the core polymerase and holoenzyme are provided.
D) The transcription bubble can be properly formed.
E) It allows RNA polymerase to distinguish between the template strand and the coding strand of the DNA molecule.

Question 5

What is required for formation of the transcription initiation complex in eukaryotes?

A) Binding of a transcription factor to the TATA box, followed by recruitment of additional transcription factors and recruitment of RNA polymerase II.
B) Binding of a transcription factor to the transcription bubble, followed by recruitment of additional transcription factors and recruitment of RNA polymerase III.
C) Binding of the sigma subunit to the start site followed by recruitment of RNA polymerase II.
D) Binding of RNA polymerase II to the TATA box, followed by recruitment of transcription factors.
E) Binding of the sigma subunit to promoter elements at -35 and -10, followed by recruitment of the core polymerase.

Question 6

You are working to characterize a novel protein in mice. Analysis shows that high levels of the primary transcript that codes for this protein are found in tissue from the brain, muscle, liver, and pancreas. However, an antibody that recognizes the C-terminal portion of the protein indicates that the protein is present in brain, muscle, and liver, but not in the pancreas. What is the most likely explanation for this result?

A) The gene that codes for this protein is not transcribed in the pancreas.
B) There is no modification of the primary transcript in the pancreas.
C) There is no modification of the primary transcript in the brain, muscle, and liver.
D) Alternative splicing in the pancreas yields a protein that is missing the portion that the antibody recognizes.
E) Alternative splicing in the brain, muscle, and liver increases the level of translation.

Question 7

A scientist makes three artificial mRNA strands:
(x) 5' AAAUUUAAAUUUAAAUUUAAAUUUAAA 3'
(y) 5' UUUCCCUUUCCCUUUCCCUUUCCCUUU 3'
(z) 5' AUAUAUAUAUAUAUAUAUAUAUAUAU 3'
When he analyzes the polypeptides produced, he finds that:
X produces a polypeptide that is 50% phenylalanine and 50%lysine.
Y produces a polypeptide that is 50% phenylalanine and 50% proline.
Z produces a polypeptide that is 50% isoleucine and 50% tyrosine.
Based on these results only, the best conclusion to make is that

A) AUA codes for isoleucine.
B) AAA codes for phenylalanine.
C) AAA codes for lysine.
D) AAA codes for lysine and AUA codes for isoleucine.
E) AAA codes for phenylalanine and AUA codes for isoleucine.

Question 8

What is the best way to describe our current understanding of the one-gene/one-polypeptide hypothesis?

A) It applies to both prokaryotes and eukaryotes.
B) It applies to prokaryotes but not to eukaryotes.
C) It applies to eukaryotes but not to prokaryotes.
D) It has been replaced by the one-gene/one-enzyme hypothesis.

Question 9

You are studying an individual with very low levels of insulin in her blood. Further analysis indicates that cells of her pancreas are producing normal levels of this protein, but most of it is accumulating in the cytoplasm rather than being secreted from the cells. Which hypothesis to explain this observation makes the most sense?

A) A small deletion has removed the nucleotides that code for the signal sequence at the amino terminus of the protein.
B) A missense mutation has caused premature termination during translation of this protein.
C) A chromosomal segment that includes the gene for insulin has been inverted.
D) A two-base deletion near the middle of the gene has altered the reading frame during translation of the protein.
E) A missense mutation has altered the ribosome-binding sequence at the 5' end of the mRNA.

Question 10

A gene that codes for a protein was removed from a eukaryotic cell and inserted into a prokaryotic cell. Although the gene was successfully transcribed, the protein translated from this transcript was different from the protein produced in the eukaryotic cell. What is the most likely explanation?

A) There are slight differences in the genetic code for prokaryotes and eukaryotes.
B) Unlike eukaryotes, which have three different RNA polymerases, prokaryotes have a single RNA polymerase.
C) Eukaryotic genes often contain introns while prokaryotic genes do not.
D) Eukaryotic transcripts have a 5' cap while prokaryotic transcripts do not.

Question 11

Shown below is a hypothetical DNA sequence from a virus. Also shown is the sequence of the RNA that is synthesized from this DNA.

DNA sequence:

5'-AGCACCTGCCGAATGGGCCAAATCCTGCCGAATAAA-3'
3'-TCGTGGACGGCTTACCCGGTTTAGGACGGCTTATTT -5'

RNA sequence (G* = G cap):

5'-G*AGCACCUGCCGCCUGCCGAAUAAAAAAA....-3'

-What is the base sequence, in the DNA template strand, of the intron that is closest to the 3' end of this strand?

A) TCGTGGACGGC
B) TTACCCGGTTTA
C) GGACGGCTTATTT
D) GCTTACCCGGTT

Question 12

How many introns does this DNA segment contain? (Enter your answer as a numeral not a word, e.g. enter 5 not five.)

Question 13

A hypothetical new organism is identified. Its genetic material consists of a single-stranded nucleic acid with six different nitrogenous bases. Just like is the case in prokaryotic and eukaryotic cells, segments of the nucleic acid contain the code for making proteins. If the genetic code in these organisms was read in groups of two bases instead of three, what is the maximum number of amino acids that could be coded for if only one codon functions as a stop codon? (Enter your answer as a numeral not a word, e.g. enter 17 not seventeen.)

Question 14

A mutation has occurred in the sequence in the promoter region of a bacterial gene, such that the sequence TTGACA has been lost. What process will be most directly affected by this mutation?

A) Transcription initiation
B) Splicing
C) Translation initiation
D) RNA polymerase II binding

Question 15

In eukaryotic cells, the 5' cap is bound to a protein complex called cap binding complex. In addition, during the splicing reaction, proteins are deposited at sites where the exons are fused together. These proteins, in combination with the cap binding complex, are essential for the recruitment of an additional complex of proteins that is essential for mRNA export from the nucleus to the cytoplasm. This complex is called the transcription-export, or TREX, complex. Taking this into account, would an mRNA encoded by a virus infecting a eukaryotic cell need to bind to the TREX complex?

A) Yes, mRNAs encoded by viruses infecting eukaryotic cells would still need to move from the nucleus to the cytoplasm to be translated.
B) No, only eukaryotic mRNAs are modified, and therefore viral mRNAs do not need to bind to the TREX complex.
C) Yes, mRNAs encoded by viruses infecting eukaryotic cells would need to bind these complexes to allow RNA processing events to occur.
D) No, mRNAs encoded by viruses infecting eukaryotic cells can be translated in the nucleus of these cells.

Question 16

A particular tRNA molecule includes the anticodon sequence: AUG. What would be the corresponding sequence in the non-coding strand of the DNA molecule that encodes the mRNA that this tRNA would pair with?

A) TAC
B) ATG
C) AUG
D) UAC

Question 17

You are interested in developing a new antibiotic for treating bacterial illnesses in humans, which is specifically toxic to bacterial cells. What processes or proteins would you want to inhibit in bacteria to generate this antibiotic?

A) The enzymes that add a 5' cap to the RNA
B) The SRP receptor
C) RNA polymerase II
D) Sigma factor binding to the holoenzyme

Question 18

What protein would be the most likely to be expected to contain a signal sequence?

A) An antibody
B) SRP
C) Aminoacyl-tRNA synthetase
D) Sigma subunit
E) Phosphofructokinase