Cell Phys: Chapter 18

1) Which of the following amino acids is not one of the 20 common amino acids found in cells? A) leucine B) isoleucine C) glutamine D) proline E) pyrrolysine

2) You are studying a eukaryotic gene whose initial transcript is 1500 nucleotides in length. The mature mRNA derived from the gene is 1200 nucleotides in length. What is the most probable reason for the discrepancy? A) a mutation that results in a shorter product B) removal of introns C) removal of exons D) mRNA breakage E) A mutation that results in a shorter product or mRNA breakage could have occurred.

3) Imagine that the genetic code were read in a non-overlapping fashion, using only two nucleotides to specify an amino acid (i.e., the sequence above would be read: AU-GA- UG and soon). Which of the following polypeptides would be obtained by translating the sequence above? A) B-B- B-B- B-B. B) B-D- B-D- B-D. C) B-B- B-D- D-D. D) B-D- E-F- G-H. E) B-D- E-B- D-E.

4) Imagine that the genetic code were read in an overlapping fashion, using three nucleotides to specify each amino acid (i.e., the sequence above would be read: AUG-UGA- GUA and so on). Which of the following polypeptides would be obtained by translating the sequence above? A) B-B- B-B- B-B- B-B- B-B. B) B-D- B-D- B-D- B-D- B-D. C) B-D- E-B- D-E- B-D- E-B. D) B-D- E-F- G-B- D-E- F-G. E) B-D- E-F- B-B- D-E- F-B.

5) Imagine that the genetic code were read in a non-overlapping fashion, using four nucleotides to specify each amino acid (i.e., the sequence above would be read: AUGA-UGAU- GUAG). Which of the following polypeptides would be obtained by translating the sequence above? A) B-B- B. B) B-D- B. C) B-D- E. D) D-D- D. E) None of these is correct.

6) According to the central dogma, the process by which information in an RNA molecule is used to direct the synthesis of a polypeptide is called A) transduction. B) translation. C) transcription. D) transition. E) transversion.

7) Consider the following double-stranded DNA sequence that codes for a short polypeptide. 5'-A- T-G- T-G- G-C- C-A- C-T- A-T- A-A- T-C- A-3' 3'-T- A-C- A-C- C-G- G-T- G-A- T-A- T-T- A-C- T-5' Which strand is the coding strand, and where is the N-terminal end of the resulting peptide located? A) The top strand is the coding strand, and the N-terminus is on the right. B) The top strand is the coding strand, and the N-terminus is on the left. C) The bottom strand is the coding strand, and the N-terminus is on the right. D) The bottom strand is the coding strand, and the N-terminus is on the left. E) Not enough information is given to answer the question.

8) Which of the following is not a true statement regarding the genetic code? A) The genetic code is degenerate. B) The genetic code is nearly universal, with only a few minor exceptions. C) The genetic code is nonoverlapping. D) The genetic code is triplet-based. E) Each codon represents a different amino acid.

9) An individual has been infected with a particular retrovirus. In order for the latent virus DNA to be inherited by subsequent generations stemming from this individual, it must be found A) in germ line cells. B) in stem cells. C) at a point early in childhood. D) in all cells simultaneously. E) in somatic cells.

10) Which of the following patterns of information flow is unique to retroviruses within a cell? A) RNA → protein B) protein → DNA C) RNA → DNA D) DNA → RNA E) protein → RNA

11) In eukaryotic cells, we sometimes find reverse transcriptase activity, even though the cells are not infected with a retrovirus. This activity can be attributed to A) the presence of transposons integrating into polymerase genes. B) the presence of viroids. C) the presence of retrotransposons. D) infection with small bacteria known as mycoplasmas. E) a novel prion infection.

12) Which of the following molecules can be considered a final product in the flow of information within a cell? A) DNA B) RNA C) protein D) lipid E) Protein or RNA can be the final product of a gene.

13) Which of the following enzymes is required in order to produce DNA molecules complementary to mRNA transcripts? A) reverse transcriptase B) reverse convertase C) DNA transcriptase D) DNA polymerase E) RNA polymerase

14) You wish to design a drug that acts against a recently identified retrovirus. Based upon what you know about retroviruses, which of the following would be the best target for specifically interrupting the viral life cycle in eukaryotic cells? A) primase B) 30S ribosomal subunits C) reverse transcriptase D) RNA polymerase E) DNA polymerase

15) The human immunodeficiency virus (HIV) is an example of a retrovirus. In order to prevent incorporation of the viral DNA into the host genome, antiretroviral drugs could A) inhibit the viral reverse transcriptase. B) inhibit retro-RNA polymerase. C) inhibit polyadenine removal. D) inhibit the viral reverse transcriptase and polyadenine removal. E) None of these are good antiretroviral strategies.

16) One consequence of the lack of introns in bacterial genes is that A) exons are eliminated during transcription. B) a 5' cap and poly (A) tail can be added immediately. C) bacterial proteins are very short and not subject to mutation. D) translation can begins before transcription is complete because prokaryotes do not have a nucleus. E) integrated viral DNA is not recognized for transcription.

17) Which of the following DNA regions is recognized by RNA polymerase during transcription? A) promoter B) operator C) attenuator D) leader E) structural gene

18) Which of the following is not a reason for the importance of mRNA processing in eukaryotes? A) longevity in the cytoplasm B) coupling of transcription and translation C) presence of a nuclear membrane D) turnover in the cytoplasm E) removal of introns

19) Which of the following enzymes is responsible for transcribing tRNA in eukaryotic cells? A) RNA polymerase I B) RNA polymerase II C) RNA polymerase III D) primase E) RNase H

20) Which of the following is not associated with mRNA processing in eukaryotes? A) addition of a 5' methyl guanosine cap B) 3' polyadenylation C) removal of introns D) removal of exons E) removal of exons and introns

21) An agent that would work well as an antibiotic against prokaryotic infection might target A) the 50S large ribosomal subunit. B) RNA polymerase II. C) the 40S small ribosomal subunit. D) DNA polymerase. E) mitochondria.

22) A new antibiotic is able to bind the rho (ρ) factor associated with some transcription processes. As a result, this antibiotic would affect A) initiation of transcription. B) elongation of transcription. C) binding of the RNA polymerase. D) termination of all transcription. E) termination of some transcription.

23) Which of the following most accurately describes the flow of information for retroviruses? A) DNA → protein B) RNA → protein C) DNA → RNA → protein D) protein → RNA → DNA → protein E) RNA → DNA → RNA → protein

24) Transcription of ribosomal RNA is primarily the function of A) primase. B) RNA polymerase I. C) RNA polymerase II. D) RNA polymerase III. E) mitochondrial RNA polymerase.

25) If you were designing a method to specifically inhibit prokaryotic transcription, but not eukaryotic transcription, interfering with which of the following would work best? A) an intercalating agent B) recognition of the prokaryotic promoter by RNA polymerase C) DNase activity D) RNA polymerase II activity E) ribosomal binding to mRNA

26) RNA polymerase II differs from RNA polymerase I and III by having A) fewer amino acids at the N-terminus. B) additional amino acids at the N-terminus. C) fewer amino acids at the C-terminus. D) additional amino acids at the C-terminus. E) individual amino acids, but all three RNA polymerases are the same size.

27) You have isolated a piece of DNA that you believe contains an interesting gene. Using a mix of RNA polymerase and ribonucleotides, you perform in vitro transcription. However, even though all of your controls work, no mRNA is created from your DNA fragment. Working backward, you note that your DNA preparation removed approximately 250 base pairs from the 5' end of the gene. The most likely explanation is that during DNA preparation A) the termination signal was removed. B) the RNA polymerase became inactivated. C) the 5' methyl guanosine cap was removed. D) the promoter was removed. E) None of these explains the negative results.

28) The action of a new drug is unknown, so you test various aspects of eukaryotic cell processes looking for an effect. You notice that the survival of cells exposed to this drug is very low. Further analysis shows that some proteins and mRNAs are much longer than they should be. One hypothesis is that the drug interferes with A) transcription termination signals. B) spliceosome activity. C) ribosomes. D) nucleoli. E) either transcription termination signals or spliceosome activity.

29) With respect to RNA processing, which of the following is false? A) RNA processing leads to the production of alternative gene products. B) Some introns are removed by spliceosomes. C) Some introns are self-splicing. D) Prokaryotic mRNAs are polyadenylated at the 3' end. E) Chemical modification occurs in tRNA transcripts.

30) The technique used to initially identity promoter sequences was A) DNA fingerprinting. B) chromosomal walking. C) DNA footprinting. D) chromatin immunoprecipitation assay. E) RNA protection.

31) In the absence of retroviruses, reverse transcription may occur in eukaryotes if which of the following is present? A) promoters B) transcription factors C) retrotransposons D) prions E) None of these are correct.

32) Which of the following is associated with the production of multiple mRNAs from a single gene? A) alternative splicing B) spliceosome mutations C) polycistronic organization D) gene rearrangement E) both spliceosome mutations and polycistronic organization

33) In some organisms, a normal stop codon, UGA, encodes for the amino acid A) leucine. B) arginine. C) isoleucine. D) selenocysteine. E) cysteine.

34) In some organisms, a special tRNA recognizes the UAG stop codon but incorporates the amino acid A) methionine. B) cysteine. C) glycine. D) pyrrolysine. E) None of these.

35) With regard to RNA polymerase proofreading ability, which of the following is true? A) RNA backtracking can remove noncomplementary nucleotides. B) RNA and DNA polymerase proofreading are essentially identical. C) There are specialized mRNA repair pathways that remove noncomplementary nucleotides. D) No proofreading occurs. E) A 3' → 5' exonuclease fixes all errors in mRNA.

36) Which of the following enzymes is associated with "transcription factories" in the nucleus? A) RNA polymerase II B) RNA polymerase I C) DNA polymerase III D) transcriptomes E) reverse transcriptase