Unit 6 Test Review

tRNA molecules deliver amino acids to ribosomes where the amino acid next

• forms an ionic bond with another amino acid

• is deaminated and catabolized

• becomes an anticodon

• is covalently bonded to a growing polypeptide

• forms hydrogen bonds with esters

In a transformation experiment, a sample of E. coli bacteria was mixed with a plasmid containing the gene for resistance to the antibiotic ampicillin (ampr). Plasmid was not added to a second sample. Samples were plated on nutrient agar plates, some of which were supplemented with the antibiotic ampicillin. The results of E. coli growth are summarized below. The shaded area represents extensive growth of bacteria; dots represent individual colonies of bacteria.

Plates that have only ampicillin-resistant bacteria growing include which of the following?

• I only

• III only

• IV only

• I and II

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NGSS.HS-LS4-4

In a transformation experiment, a sample of E. coli bacteria was mixed with a plasmid containing the gene for resistance to the antibiotic ampicillin (ampr). Plasmid was not added to a second sample. Samples were plated on nutrient agar plates, some of which were supplemented with the antibiotic ampicillin. The results of E. coli growth are summarized below. The shaded area represents extensive growth of bacteria; dots represent individual colonies of bacteria.

Which of the following best explains why there is no growth on plate II?

• The initial E. coli culture was not ampicillin-resistant.

• The transformation procedure killed the bacteria.

• Nutrient agar inhibits E. coli growth.

• The bacteria on the plate were transformed.

In a transformation experiment, a sample of E. coli bacteria was mixed with a plasmid containing the gene for resistance to the antibiotic ampicillin (ampr). Plasmid was not added to a second sample. Samples were plated on nutrient agar plates, some of which were supplemented with the antibiotic ampicillin. The results of E. coli growth are summarized below. The shaded area represents extensive growth of bacteria; dots represent individual colonies of bacteria.

Plates I and III were included in the experimental design in order to

• demonstrate that the E. coli cultures were viable

• demonstrate that the plasmid can lose its ampr gene

• demonstrate that the plasmid is needed for E. coli growth

• prepare the E. coli for transformation

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NGSS.HS-LS3-2

In a transformation experiment, a sample of E. coli bacteria was mixed with a plasmid containing the gene for resistance to the antibiotic ampicillin (ampr). Plasmid was not added to a second sample. Samples were plated on nutrient agar plates, some of which were supplemented with the antibiotic ampicillin. The results of E. coli growth are summarized below. The shaded area represents extensive growth of bacteria; dots represent individual colonies of bacteria.

Which of the following statements best explains why there are fewer colonies on plate IV than on plate III?

• Plate IV is the positive control.

• Not all E. coli cells are successfully transformed.

• The bacteria on plate III did not mutate.

• The plasmid inhibits E. coli growth.

Tags

NGSS.HS-LS3-2

In a transformation experiment, a sample of E. coli bacteria was mixed with a plasmid containing the gene for resistance to the antibiotic ampicillin (ampr). Plasmid was not added to a second sample. Samples were plated on nutrient agar plates, some of which were supplemented with the antibiotic ampicillin. The results of E. coli growth are summarized below. The shaded area represents extensive growth of bacteria; dots represent individual colonies of bacteria.

In a second experiment, the plasmid contained the gene for human insulin as well as the ampr gene. Which of the following plates would have the highest percentage of bacteria that are expected to produce insulin?

• I only

• III only

• IV only

• I and III

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NGSS.HS-LS3-2

The regulatory sequences of the operon controlling arabinose metabolism (ara operon) were studied to determine whether bacteria can respond to changes in nutrient availability. It is predicted that if those regulatory sequences are functioning properly, the bacteria will produce the enzymes involved in arabinose metabolism (structural genes B, A, and D) in the presence of arabinose.

If a gene that encodes a green fluorescent protein (GFP) is substituted for the structural genes of the operon, activation of the regulatory sequences can be assayed by GFP expression. A culture of E. coli cells underwent a transformation procedure with a plasmid containing the regulatory sequences of the ara operon directly upstream of the gene encoding the GFP. The plasmid also confers ampicillin resistance to bacteria. Samples were then plated on different types of culture media. (Note: The GFP fluoresces only under UV light, not under white light.) The table below shows the results.

Which of the following can best be used to justify why the GFP is expressed by E. coli cells after transformation with the plasmid?

• The presence of arabinose in the nutrient agar activated the expression of the genes located downstream of the ara operon regulatory sequences.

• The combination of ampicillin and arabinose in the nutrient agar inhibited the expression of certain gene products, resulting in the increased expression of the GFP.

• The nutrient agar without arabinose but with ampicillin activated the expression of the genes located downstream of the ara operon regulatory sequences.

• Both arabinose and ampicillin were required in the nutrient agar to activate the expression of genes located downstream of the ara operon regulatory sequences.

Arctic foxes typically have a white coat in the winter. In summer, when there is no snow on the ground, the foxes typically have a darker coat.

Which of the following is most likely responsible for the seasonal change in coat color?

• The decrease in the amount of daylight in winter causes a change in gene expression, which results in the foxes growing a lighter-appearing coat.

• The diet of the foxes in summer lacks a particular nutrient, which causes the foxes to lose their white coat and grow a darker-colored coat.

• Competition for mates in the spring causes each fox to increase its camouflage with the environment by producing a darker-appearing coat.

• The lower temperatures in winter denature the pigment molecules in the arctic fox coat, causing the coat to become lighter in color.

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NGSS.MS-LS1-5

Arsenic is a toxic element found in both aquatic and terrestrial environments. Scientists have found genes that allow bacteria to remove arsenic from their cytoplasm. Arsenic enters cells as arsenate that must be converted to arsenite to leave cells. Figure 1 provides a summary of the arsenic resistance genes found in the operons of three different bacteria.E. coliR773 is found in environments with low arsenic levels. Herminiimonas arsenicoxydans and Ochrobactrum tritici are both found in arsenic‑rich environments. Researchers claim that bacteria that live in environments heavily contaminated with arsenic are more efficient at processing arsenic into arsenite and removing this toxin from their cells. Justify this claim based on the evidence shown in Figure 1.

• There are multiple operons controlling the production of proteins that process and remove arsenite from cells in both H. arsenicoxydans and O. tritici. In contrast, E. coli has only one operon devoted to arsenic removal.

• Both H. arsenicoxydans and O. tritici contain the ars R gene that codes for a repressor that turns on the operon to eliminate arsenite from the cell.

• Both O. tritici andE. coli contain the ars D gene, which codes for a protein that helps remove arsenite from the cell.

• Both H. arsenicoxydans and O. tritici. have more arsenic resistance genes than has E. coli.

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NGSS.HS-LS3-2

Ascorbic acid (vitamin C) is an organic molecule necessary for the health of plants and animals. The majority of animals, including most mammals, synthesize ascorbic acid from organic precursors, but some primates are unable to synthesize ascorbic acid and must instead acquire it from dietary sources, such as certain fruits and vegetables.

The L-gulonolactone oxidase (GULO) gene encodes an enzyme that catalyzes a required step in the biosynthesis of ascorbic acid. Most mammals carry a functional copy of the GULO gene, but some primates carry only a GULO pseudogene, which is a nonfunctional variant.

A comparison of GULO genes and GULO pseudogenes from different animals can provide insight into the evolutionary relatedness of the animals. In Table I, selected members of some mammalian groups are listed, along with an indication of their ability to synthesize ascorbic acid. Table II shows an alignment of amino acid coding sequences from homologous regions of the GULO genes and GULO pseudogenes of the organisms listed in Table I. Figure 1 represents the universal genetic code. Comparison of DNA sequences in Table II suggests that a functional GULO gene in lemurs can have a G, C, or T at position 21 but only a G at position 22. Which of the following pairs of predictions is most helpful in explaining the discrepancy?

• A substitution at position 21 would result in no change in protein. A substitution at position 22 would result in a premature stop codon or an amino acid with different

  biochemical characteristics.

• A substitution at position 21 would result in a different amino acid. A substitution at position 22 would result in a premature stop codon or an amino acid with different

  biochemical characteristics.

• A substitution at position 21 would result in no change in protein. A substitution at position 22 would result in a frame shift producing an inactive protein

• A substitution at position 21 would result in an amino acid with different biochemical characteristics. A substitution at position 22 would result in no transcription of the gene

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NGSS.HS-LS3-2

NGSS.HS-LS3-1