Unit 6

Analysis of DNA sequences from two individuals of the same species results in a greater estimate of genetic variability than does analysis of amino acid sequences from the same individuals because A) different DNA sequences can code for the same amino acid B) some amino acid variations cannot be detected by protein electrophoresis C) DNA sequencing is a more reliable technique than protein electrophoresis D) proteins are more easily damaged than is DNA E) DNA is more heat-sensitive and therefore varies more

A) different DNA sequences can code for the same amino acid

The human TPM1 gene encodes members of the tropomyosin family of cytoskeletal proteins. Which of the following best explains how different proteins can be made in different cell types from the one TPM1 gene? A) Different introns are selectively converted to exons. B) Different exons are retained or spliced out of the primary transcript. C) The GTP cap is selectively added to and activates different exons. D) Different portions of the primary transcript remain bound to the template DNA.

B) Different exons are retained or spliced out of the primary transcript.

Which of the following correctly explains the process shown in Figure 1? A) DNA replication is occurring because replication is semi-conservative and the new strand is a copy of the template strand. B) Initiation of transcription is occurring because a strand of RNA is being produced from a DNA template strand. C) Translation is occurring because the two strands have separated and a new strand is being produced. D) Alternative splicing of mRNA is occurring because the mRNA strand is being synthesized from only one strand of DNA.

B) Initiation of transcription is occurring because a strand of RNA is being produced from a DNA template strand.

Erwin Chargaff investigated the nucleotide composition of DNADNA. He analyzed DNADNA from various organisms and measured the relative amounts of adenine (AA), guanine (GG), cytosine (CC), and thymine (TT) present in the DNADNA of each organism. Table 1 contains a selected data set of his results. Which of the following statements best explains the data set? A) Since the %A%A and the %G%G add up to approximately 50 percent in each sample, adenine and guanine molecules must pair up in a double-stranded DNADNA molecule. B) Since the %A%A and the %T%T are approximately the same in each sample, adenine and thymine molecules must pair up in a double-stranded DNADNA molecule. C) Since the %(A+T)%(A+T) is greater than the %(G+C)%(G+C) in each sample, DNADNA molecules must have a poly-AA tail at one end. D) Since the %C%C and the %T%T add up to approximately 50 percent in each sample, cytosine and thymine molecules must both contain a single ring.

B) Since the %A%A and the %T%T are approximately the same in each sample, adenine and thymine molecules must pair up in a double-stranded DNADNA molecule.

Which of the following correctly explains where DNA replication will begin on the strand oriented 5'→3', reading from left to right? A) DNA replication will be randomly initiated along the unwound portion of the DNA strand since base pairing will occur. B) DNA replication cannot occur since there is already RNA base pairing with the template strand. C) DNA replication will be initiated immediately to the left of the RNA, since DNA polymerase requires an RNA primer. D) DNA replication will be initiated at the site of the topoisomerase since that is where DNA begins to uncoil.

C) DNA replication will be initiated immediately to the left of the RNA, since DNA polymerase requires an RNA primer.

Which of the following best describes the most likely effect of the formation of a triplex DNA structure (Figure 3) on the synthesis of the frataxin protein? A) The binding of the ribosome to the mRNA is prevented, resulting in a decrease in frataxin translation. B) The DNA will not degrade in the cytoplasm, leading to an increase in frataxin translation. C) RNA polymerase is prevented from binding to the DNA, resulting in a decrease in frataxin mRNA transcription. D) The protein will include extra amino acids, resulting in a protein with an altered secondary structure.

C) RNA polymerase is prevented from binding to the DNA, resulting in a decrease in frataxin mRNA transcription.

Retroviruses have an RNA genome. HTLV-1 is a lysogenic retrovirus that establishes a latent infection in human cells. By which of the following mechanisms does infection by a retrovirus such as HTLV-1 most likely cause long-lasting genetic changes to host cells? A) The host-cell ribosomes translate the viral RNA genome that enters the cell upon initial viral infection. B) The viral RNA polymerase that transcribes host genes has a high error rate. C) The RNA viral genome is reverse transcribed into DNA that integrates into the host genome. D) The RNA viral genome integrates into the host genome.

C) The RNA viral genome is reverse transcribed into DNA that integrates into the host genome.

Which of the following best explains how the expression of a eukaryotic gene encoding a protein will differ if the gene is expressed in a prokaryotic cell instead of in a eukaryotic cell? A) No transcript will be made, because eukaryotic DNA cannot be transcribed by prokaryotic RNA polymerase. B) The protein will have a different sequence of amino acids, because prokaryotes use a different genetic code. C) The protein will be made but will not function, because prokaryotes cannot remove introns. D) The protein will not be made, because prokaryotes lack the ribosomes necessary for translation.

C) The protein will be made but will not function, because prokaryotes cannot remove introns.

When DNA replicates, each strand of the original DNA molecule is used as a template for the synthesis of a second, complementary strand. Which of the following figures most accurately illustrates enzyme-mediated synthesis of new DNA at a replication fork?

D) Lagging from 3' to 5' and leading from 5' to 3'

Antibiotics interfere with prokaryotic cell functions. Streptomycin is an antibiotic that affects the small ribosomal subunit in prokaryotes. Specifically, streptomycin interferes with the proper binding of tRNA to mRNA in prokaryotic ribosomes. Which of the following best predicts the most direct effect of exposing prokaryotic cells to streptomycin? A) Amino acid synthesis will be inhibited. B) No mRNA will be transcribed from DNA. C) Posttranslational modifications will be prevented. D) Synthesis of polypeptides will be inhibited.

D) Synthesis of polypeptides will be inhibited.

Which of the following statements best explains the structure and importance of plasmids to prokaryotes? A) Plasmids are circular, single-stranded RNARNA molecules that transfer information from the prokaryotic chromosome to the ribosomes during protein synthesis. B) Plasmids are circular, double-stranded DNADNA molecules that provide genes that may aid in survival of the prokaryotic cell. C) Plasmids are single-stranded DNADNA molecules, which are replicated from the prokaryotic chromosome, that prevent viral reproduction within the prokaryotic cell. D) Plasmids are double-stranded RNARNA molecules that are transmitted by conjugation that enable other prokaryotic cells to acquire useful genes.

Plasmids are circular, double-stranded DNA molecules that provide genes that may aid in survival of the prokaryotic cell.

Which of the following best illustrates the flow of information required for the synthesis of proteins encoded in the genome of a retrovirus?

RNA -> DNA -> RNA -> Protein

Figure 1 represents part of a process essential to gene expression. Which of the following best explains what strand X represents? A) A complementary RNA sequence, because it contains thymine B) The coding strand in this process, because it is being read 3′ to 5′ C) The antisense strand, because it is serving as a template D) The pre‑mRNA, because it does not yet have a GTP cap

The antisense strand, because it is serving as a template Antisense = Template strand

Which of the following statements best explains how the genes for antibiotic resistance can be transmitted between bacteria without the exchange of bacterial chromosomal DNA? A) The antibiotic-resistant bacteria release a hormone that signals neighboring bacteria to become resistant. B) The genes for antibiotic resistance are located on a plasmid that can be passed to neighboring bacteria. C) The antibiotic-resistant bacteria are the result of bacteria that specifically modify their own chromosomal DNADNA to neutralize the antibiotics. D) The antibiotic alters the bacterial genome of each bacterium, which results in an antibiotic-resistant population.

The genes for antibiotic resistance are located on a plasmid that can be passed to neighboring bacteria.

A tobacco plant can be made to express a gene from fireflies, resulting in the emission of light. Which of the following is the basis for this phenomenon? A) Chloroplasts can be made to produce light if firefly proteins are injected into plant cells. B) Fireflies and tobacco plants share a recent common ancestor. C) Fireflies and tobacco plants are infected by the same kinds of bacteria. D) Transcription and translation are fundamen-tally similar in both fireflies and tobacco plants. E) Most enzymes in fireflies have the same amino acid sequence as the enzymes in tobacco plants.

Transcription and translation are fundamen-tally similar in both fireflies and tobacco plants.