Unit 6 MCQ

Question 1

Which of the following statements best explains the data set?

Answer 1

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.

Question 2

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?

Answer 2

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

Question 3

Which of the following statements best explains the structure and importance of plasmids to prokaryotes?

Answer 3

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

Question 4

Which of the following best explains what process is represented in Figure 1 ?

Answer 4

New DNA strands are being synthesized in the 5’ to 3’ direction for their DNA templates.

Question 5

The features of this model provide evidence for which explanation of why all growing strands are synthesized in a 5′ to 3′ direction?

Answer 5

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.

Question 6

Which of the following correctly explains where DNA replication will begin on the strand oriented 5’→3’, reading from left to right?

Answer 6

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

Question 7

A model that represents a process occurring in a cell of a particular organism is shown in Figure 1.

Figure 1. Process occurring in a cell

Which of the following correctly explains the process shown in Figure 1 ?

Answer 7

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

Question 8

Figure 1 represents part of a process that occurs in eukaryotic cells. There are untranslated regions (UTR) in this sequence.

Figure 1. Cellular process involving nucleic acids

Which of the following best explains the process represented by Figure 1 ?

Answer 8

The enzyme-regulated processing of pre‑ mRNA into mature mRNA

Question 9

Figure 1 represents part of a process essential to gene expression.

Figure 1. Model of process involved in gene expression.

Which of the following best explains what strand X represents?

Answer 9

The antisense strand, because it is serving as a template

Question 10

Histone methyl transferases are a class of enzymes that methylate certain amino acid sequences in histone proteins. A research team found that transcription of gene R decreases when histone methyl transferase activity is inhibited.

Which scientific claim is most consistent with these findings?

Answer 10

Histone methylation opens up chromatin at gene R so transcription factors can bind to DNA more easily.

Question 11

Figure 1 represents a metabolic process involving the regulation of lactose metabolism by E. coli bacteria. Lactose is utilized for energy by E. coli when glucose is not present. Allolactose is an isomer of lactose that is in the environment of these bacteria when lactose is present. The CAP site prevents the binding of RNA polymerase when glucose is present in the environment. The lacZ, lacY, and lacA genes code for proteins needed for lactose metabolism.

Figure 1. Model of lac operon, comparing repressed and active states

Which is a scientific claim that is consistent with the information provided and Figure 1 ?

Answer 11

When bound to the operator, the repressor protein prevents lactose metabolism in E. coli.

Question 12

Figure 1 illustrates processes related to control of transcription and translation in a cell.

Which of the following scientific claims is most consistent with the information provided in Figure 1 ?

Answer 12

Different genes may be regulated by the same transcription factor.

Question 13

Molecular biologists are studying the processes of transcription and translation and have found that they are very similar in prokaryotes and eukaryotes, as summarized in Table 1.

Based on the information in Table 1, which of the following best predicts a key difference in prokaryotes and eukaryotes with regard to transcription and translation?

Answer 13

The two processes will occur simultaneously in prokaryotes but not eukaryotes.

Question 14

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?

Answer 14

Synthesis of polypeptides will be inhibited.

Question 15

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. coli R773 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.

Answer 15

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.

Question 16

Both liver cells and lens cells have the genes for making the proteins albumin and crystalline. However, only liver cells express the blood protein albumin and only lens cells express crystalline, the main protein in the lens of the eye. Both of these genes have enhancer sequences associated with them.

The claim that gene regulation results in differential gene expression and influences cellular products (albumin or crystalline) is best supported by evidence in which of the following statements?

Answer 16

Liver cells possess transcriptional activators that are different from those of lens cells.

Question 17

Phytochromes are molecules that change light stimuli into chemical signals, and they are thought to target light-activated genes in plants. A study was conducted to determine how certain cell proteins were made in a plant cell using a phytochrome. Figures 1 and 2 represent findings from the study.

Use the response models shown in Figures 1 and 2 to justify the claim that phytochromes regulate the transcription of genes leading to the production of certain cellular proteins.

Answer 17

When inactive phytochrome Pr is activated by red light to become phytochrome Pfr , it is transported into the nucleus where it binds to the transcription factor PIF3 at the promoter. This stimulates transcription, ultimately leading to protein production. Far-red light inactivates the phytochrome, which will turn transcription off by not binding to PIF3 .

Question 18

Antigens are foreign proteins that invade the systems of organisms. Vaccines function by stimulating an organism’s immune system to develop antibodies against a particular antigen. Developing a vaccine involves producing an antigen that can be introduced into the organism being vaccinated and which will trigger an immune response without causing the disease associated with the antigen. Certain strains of bacteria can be used to produce antigens used in vaccines.

Which of the following best explains how bacteria can be genetically engineered to produce a desired antigen?

Answer 18

The gene coding for the antigen can be inserted into plasmids that can be used to transform the bacteria.

Question 19

Students subjected three samples of five different molecules to gel electrophoresis as shown in Figure 1.

Figure 1. Gel electrophoresis of three prepared samples

Which of the following statements best explains the pattern seen on the gel with regard to the size and charge of molecules A and B?

Answer 19

Molecules A and B are negatively charged, and molecule A is smaller than molecule B .

Question 20

Genetic engineering techniques can be used when analyzing and manipulating DNA and RNA. Scientists used gel electrophoresis to study transcription of gene L and discovered that mRNA strands of three different lengths are consistently produced.

Which of the following explanations best accounts for this experimental result?

Answer 20

Pre- mRNA of gene L is subject to alternative splicing, so three mRNA sequences are possible.

Question 21

The enzyme lactase aids in the digestion of lactose, a sugar found in the milk of most mammals. In most mammal species, adults do not produce lactase. Continuing to produce lactase into adulthood in people is called lactase persistence. A number of different alleles have been identified that result in lactase persistence. Figure 1 shows the percentage of people in different geographic areas parts of the Old World that exhibit lactase persistence.

Figure 1. Distribution of lactase persistence in Europe, North Africa, and parts of Asia

Which of the following best explains the distribution of lactase persistence in the areas shown in Figure 1 ?

Answer 21

Mutations conferring lactase persistence likely arose independently in different geographic areas and offered a selective advantage.

Question 22

Nondisjunction during meiosis can negatively affect gamete formation. A model showing a possible nondisjunction event and its impact on gamete formation is shown in Figure 1.

Which of the following best describes the most likely impact on an individual produced from fertilization between one of the daughter cells shown and a normal gamete?

Answer 22

Because nondisjunction occurred in anaphase I , all gametes will have an abnormal chromosome number and the individual will likely exhibit phenotypic evidence of the nondisjunction event.

Question 23

Sickle-cell anemia is an inherited blood disorder in which one of the hemoglobin subunits is replaced with a different form of hemoglobin. Partial DNA sequences of the HBB gene for normal hemoglobin and for sickle-cell hemoglobin are shown in Figure 1.

Partial sequence for normal hemoglobin:

Which of the following best describes the type of mutation shown in Figure 1 that leads to sickle-cell anemia?

Answer 23

Substitution

Question 24

Which of the following statements best explains the experimental results observed in Figure 1 ?

Answer 24

E. coli in lane CC have been successfully transformed and contain additional genetic information.

Question 25

Which of the following best explains how the pattern of DNA arrangement in chromosomes could be used, in most cases, to determine if an organism was a prokaryote or a eukaryote?

Answer 25

Prokaryotic DNA Single circular chromosome Eukaryotic DNA Multiple linear chromosomes

Question 26

Which of the following best explains how the results should be interpreted?

Answer 26

The individual has an increased risk of developing colon cancer.

Question 27

Given the results shown in Figure 1, which of the following correctly describes a relationship between the two species?

Answer 27

Species B has more short fragments of DNA than species A does.

Question 28

Which of the following best helps explain how the process represented in Figure 1 produces DNA molecules that are hybrids of the original and the newly synthesized strands?`

Answer 28

Each newly synthesized strand remains associated with its template strand to form two copies of the original DNA molecule.

Question 29

Which of the following best predicts what will happen when a normal cell is exposed to a retrovirus?

Answer 29

The reverse transcriptase will produce DNA from the viral RNA, which can be incorporated into the host’s genome and then transcribed and translated.

Question 30

Which of the following statements best explains what is shown in Figure 1 ?

Answer 30

UV photons cause dimers to form, leading to misshapen DNA, which results in replication and transcription errors.

Question 31

Which of the following evidence best supports a claim that tryptophan functions as a corepressor?

Answer 31

When trpR is mutated, the trp operon is transcribed regardless of tryptophan levels.

Question 32

A cell needs to metabolize the substrate illustrated in Figure 1 for a vital cellular function. Which of the following best explains the long-term effect on the cell of splicing that yields only enzyme C mRNA?

Answer 32

The cell will die because it is unable to metabolize the substrate without enzyme AA, which is structurally specific for the substrate shown.

Question 33

Which of the following statements best explains the role of Enzyme 1 in the DNA replication process?

Answer 33

Enzyme 1 is a topoisomerase that relieves tension in the overwound DNA in front of a replication fork.

Question 34

Which of the following claims about the TYR, TRP2, and TRP1 mammalian genes is most likely to be accurate?

Answer 34

The TYR, TRP2, and TRP1 genes may be located on different chromosomes but are activated by the same transcription factor.

Question 35

Which of the following claims best explains why keratinocytes do not produce melanin?

Answer 35

Keratinocytes do not express the MITF gene.

Question 36

Based on the information provided in Figure 1 and Figure 2, which of the following best predicts the effects of a mutation in the promoter of the TYR gene that prevents it from being transcribed?

Answer 36

Skin pigmentation will not be able to change, resulting in a negative selection pressure.

Question 37

Which of the following best explains a process occurring between point 1 and point 2 in Figure 3 ?

Answer 37

A poly‑A tail is added to RNA.

Question 38

Which of the following best predicts the phenotype of an individual who is homozygous for this TYR mutation?

Answer 38

The mutation will change all subsequent amino acids in the TYR protein, leading to nonfunctional TYR protein. Individuals with this mutation will lack melanin in their hair, skin, and eyes and will not tan in response to UV radiation.

Question 39

Which of the following best supports the claim that binding of miRNA‑delta to the miRNA binding site inhibits translation of gene Q mRNA?

Answer 39

When the miRNA binding site sequence is altered, translation of Q mRNA occurs in the presence of miRNA-delta.

Question 40

Which of the following statements provides the best explanation of the processes illustrated in Figure 1 ?

Answer 40

Sections of the pre-rRNA are removed, and the mature rRNA molecules are available to combine with proteins to form the ribosomal subunits.

Question 41

A woman develops Huntington’s disease. Her father had the disorder. Her mother did not, and there is no history of the disorder in the mother’s family. Which of the following best explains how the woman inherited Huntington’s disease?

Answer 41

She inherited an allele with more than 40 CAG repeats in the HTT gene from her father.

Question 42

Which of the following best explains how this model illustrates DNA replication of both strands as a replication fork moves?

Answer 42

II is synthesized continuously in the 5′ to 3′ direction, and III is synthesized in segments in the 5′ to 3′ direction.

Question 43

Which claim is most consistent with the information provided by the diagram and current scientific understanding of gene regulation and expression?

Answer 43

Some sequences of DNA can interact with regulatory proteins that control transcription.

Question 44

Based on the information in Figure 1, which type of mutation explains the nature of the change in DNA that resulted in cystic fibrosis in the affected individual?

Answer 44

Deletion, because a thymine is missing, which changes the reading frame.

Question 45

Nucleotide base pairing in DNA is universal across organisms. Each pair (T−A; C−G) consists of a purine and a pyrimidine. Which of the following best explains how the base pairs form?

Answer 45

Hydrogen bonds join a double-ringed structure to a single-ringed structure in each pair.