AP Bio Chapter 16/17 multiple choice

Which of the following is most likely to create genetic variation in a population?

DNA polymerase errors during replication

figure 1 illustrates a model of the molecules involved in DNA replication and their placement relative to each other. Which of the following correctly explains where DNA replication will begin on the strand oriented 5'→3', reading from left to right?

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

A mutation that affects Pitx1 gene function in all tissue types is most likely to be at which of the following genetic loci?

Promoter

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

The table below describes the action of two genes involved in the regulation of nervous system development in the nematode C. elegans. Which of the following claims is best supported by the data?

Gene A promotes neuron development; gene B promotes programmed cell death in neuronal precursors.

Histone methyltransferases 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 methyltransferase activity is inhibited. Which scientific claim is most consistent with these findings?

Histone methylation opens up chromatin at gene RR so transcription factors can bind to DNADNA more easily

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 ?

Initiation of transcription is occurring because a strand of RNARNA is being produced from a DNADNA template strand.

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?

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

Based on the universal genetic code, which of the following represents the correct polypeptide that will result from translation of the mRNA molecule shown, beginning with the first available start codon?

Met−Val−Thr−Lys−Phe−Gly−His

Figure 1 represents part of a process essential to gene expression. Which of the following best explains what strand X represents?

The antisense strand, because it is serving as a template

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.

Which of the following is the most likely effect of the mutation at nucleotide position 7 in the GULO gene of humans?

The deletion of the single nucleotide causes a frame shift, changing the primary structure downstream of the mutation and resulting in a nonfunctional protein.

Lactose digestion in E. coli begins with its hydrolysis by the enzyme β-galactosidase. The gene encoding β-galactosidase, lacZ, is part of a coordinately regulated operon containing other genes required for lactose utilization. Which of the following figures correctly depicts the interactions at the lac operon when lactose is NOT being utilized? (The legend below defines the shapes of the molecules illustrated in the options.)

Promoter- Open operator- LacZ-LacY-LacA

The figure above depicts the DNA-protein complex that is assembled at the transcriptional start site of gene X when the expression of gene X is activated in liver cells. Previous studies have shown that gene X is never expressed in nerve cells. Based on the diagram, which of the following most likely contributes to the specific expression pattern of gene X ?

The activator is a sequence-specific DNA-binding protein that is present in some tissues but not in other tissues.

In sticklebacks, which of the following is most likely to occur if the jaw enhancer is disabled instead of the hindlimb enhancer?

The jaw does not develop normally, but a pronounced pelvic spine does develop because the Pitx1 gene is expressed in the developing pelvis but not in the developing jaw.

The diagram above represents a segment of the E. coli chromosome that contains the lacI gene and part of the lac operon, a coordinately regulated set of genes that are required for the metabolism of lactose. The presence of lactose, which causes the repressor to be released from the operator, results in increased transcription of the lac operon. Which of the following best explains the contribution of the lac operon to the metabolic efficiency of a bacterial cell?

The lacZ gene is highly expressed only when lactose is available

In animals, the hox genes encode a family of transcription factors that are important for proper development of embryonic segments and are widely conserved in organisms. The figure below shows the embryonic segments in which one such gene, Hoxc6, is expressed in the embryo of a mouse, a chick, and a goose. Embryonic segments are counted from the anterior end. During the formation of vertebrae, the most anterior embryonic segment that expresses Hoxc6 marks the end of the cervical (neck) vertebrae and the beginning of the thoracic (rib) vertebrae. All mammals have seven cervical vertebrae. Which of the following statements is most likely to be true?

The most anterior expression of Hoxc6 is the eighth vertebra in mammals.

The following the DNA sequence is a small part of the coding (nontemplate) strand from the open reading frame of β-hemoglobin gene. Given the codon chart listed below, what would be the effect of a mutation that deletes the G at the beginning of the DNA sequence?

The reading frame of the sequence would shift, causing a change in the amino acid sequence after that point.

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

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

The Trp operon is a coordinately regulated group of genes (trpA-trpE) that are required for tryptophan biosynthesis in E. coli. Based on the figure above, which of the following correctly describes the regulation of the Trp operon?

In the presence of tryptophan, the repressor is active and binds to the Trp operator, preventing RNA polymerase from transcribing the operon.

Mutations in DNA are usually caused by chemical or radiation damage to DNA molecules, followed by imperfect repair of the damage. Immediately after this kind of imperfect repair, there may be a mismatched base pair in the DNA. The illustration below shows an example of a mismatch, with the relevant pair bases in bold. Which of the following best represents the DNA of the two daughter cells produced when a bacterial cell with this particular mismatch replicates its DNA and divides?

AT Mutant and GC Normal

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

Substitution

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?

Synthesis of polypeptides will be inhibited.

Sickle-cell anemia results from a point mutation in the HBB gene. The mutation results in the replacement of an amino acid that has a hydrophilic R-group with an amino acid that has a hydrophobic R-group on the exterior of the hemoglobin protein. Such a mutation would most likely result in altered

properties of the molecule as a result of abnormal interactions between adjacent hemoglobin molecules

Sickle-cell anemia is associated with a mutation in the gene encoding the beta subunit of hemoglobin that results in a change from glutamic acid to valine at position 6. All other amino acids are identical to a normal hemoglobin molecule. Based on the information above, which of the following mutations is the most likely cause of sickle-cell anemia?

A single base-pair substitution in the gene encoding the beta subunit

A model of a process involving nucleic acids is shown in Figure 1. Which of the following best explains what process is represented in Figure 1 ?

New DNADNA strands are being synthesized in the 5'5′ to 3'3′ direction from their DNADNA templates.

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?

No change to the protein, A premature stop codon or an amino acid with different biochemical characteristics

Phenotype is determined, in part, by which genes are expressed. The diagram below illustrates how the product of gene Xregulates the expression of other genes. Which of the following statements best explains how protein X regulates gene expression?

Protein X is responsible for activating transcription of some genes but not others.

Figure 1 shows some relevant details of a model of how a deoxynucleotide, in this case dTMP, is added to a growing strand of DNA. Figure 1. Model showing details of adding a deoxythymidine monophosphate (dTMP) nucleotide to a growing strand of DNA The features of this model provide evidence for which explanation of why all growing strands are synthesized in a 5′ to 3′ direction?

The phosphate group, attached to the 5′5′ carbon of the dTMPdTMP, forms a covalent bond with the oxygen atom attached to the 3′3′ carbon of the growing strand.

The diagram above represents a segment of the E. coli chromosome that contains the lacI gene and part of the lac operon, a coordinately regulated set of genes that are required for the metabolism of lactose. The presence of lactose, which causes the repressor to be released from the operator, results in increased transcription of the lac operon. Which of the following is the most likely consequence of a mutation at the operator locus that prevents binding of the repressor protein?

Beta-galactosidase will be produced, even in the absence of lactose.

Nuclear pores regulate the passage of substances into and out of the nucleus. Antibodies such as mAb414 have been used to inhibit the movement of substances through the nuclear pores of rat liver cells. Scientists cultured rat liver cells (eukaryotic) and bacteria cells (prokaryotic) in separate dishes with radioactively labeled amino acids. A specific gene in both cell types was engineered to synthesize identical polypeptide chains, and translation of this gene was measured. The procedure was repeated with mAb414 (the inhibitor) added to each of the two cell cultures, and translation was monitored again. Which of the following sets of graphs best summarizes the results of the experiments?

D

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 ?

Different genes may be regulated by the same transcription factor.

As represented in Figure 1 and Figure 2, the phenotypic difference between marine and freshwater sticklebacks involves Pitx1, a gene that influences the formation of the jaw, pituitary gland, and pelvic spine. Enhancer sequences upstream of the Pitx1 genetic locus regulate expression of the Pitx1 gene at the appropriate times and in the appropriate tissues during development. Previous studies have found that a mutation in the hindlimb enhancer interferes with the formation of a pronounced pelvic spine. Which of the following best describes how sticklebacks in the same population with identical copies of the Pitx1 gene can still show phenotypic variation in the pelvic spine character?

Expression of the Pitx1 gene is affected by mutations at other genetic loci.

Which of the following best describes an event during step 2 in the simplified model above?

Noncoding sequences are removed from a newly synthesized RNA molecule.

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.

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.

Figure 1 represents part of a process that occurs in eukaryotic cells. There are untranslated regions (UTR) in this sequence. Which of the following best explains the process represented by Figure 1 ?

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

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?

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

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.

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.

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.

When inactive phytochrome PrPr is activated by red light to become phytochrome PfrPfr, it is transported into the nucleus where it binds to the transcription factor PIF3PIF3 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 PIF3PIF3.