unit 6 mc

Which of the following best explains what process is represented in Figure 1 ? A. New DNA strands are being synthesized in the 3′ to 5′ direction from their DNA templates. B. New DNA strands are being synthesized in the 5′ to 3′ direction from their DNA templates. C. A new RNA strand is being synthesized in the 3′ to 5′ end from its DNA template. D. Two new RNA strands are being synthesized in both directions from their DNA templates.

B

Antibiotics can be used to kill the specific pathogenic bacterium, Mycobacterium tuberculosis, that causes tuberculosis. The appearance of antibiotic-resistant strains has made it more difficult to cure M. tuberculosis infections. These antibiotic-resistant bacteria survive and pass on the genes to their offspring, making the resistant phenotype more common in the population. DNA analysis indicates that the genes for antibiotic resistance are not normally present in bacterial chromosomal DNA. 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 DNA to neutralize the antibiotics. D. The antibiotic alters the bacterial genome of each bacterium, which results in an antibiotic-resistant population.

B

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

B

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

B

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

The features of this model provide evidence for which explanation of why all growing strands are synthesized in a 5′ to 3′ direction? A. The two strands need to be antiparallel to bond properly. B. Thymine and adenine would not bond properly if the strand grew from 3′ to 5′. C. The translation of mRNA occurs in the 5′ to 3′ direction; therefore, the growing DNA strand must also grow in the 5′ to 3′ direction. D. The phosphate group, attached to the 5′ carbon of the dTMP, forms a covalent bond with the oxygen atom attached to the 3′ carbon of the growing strand.

D