ap bio unit 6

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? A Liver cells possess transcriptional activators that are different from those of lens cells. B Liver cells and lens cells use different RNARNA polymerase enzymes to transcribe DNA. C Liver cells and lens cells possess the same transcriptional activators. D Liver cells and lens cells possess different general transcription factors.

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

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? A The gene coding for the antigen can be inserted into plasmids that can be used to transform the bacteria. B The bacteria need to be exposed to the antigen so they can produce the antibodies. C The DNADNA of the antigen has to be transcribed in order for the mRNA produced to be inserted into the bacteria. D The mRNA of the antigen has to be translated in order for the protein to be inserted into the bacteria.

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

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? A The two processes will occur simultaneously in prokaryotes but not eukaryotes. B Prokaryotic mRNA is shorter than eukaryotic mRNA. C Eukaryotic mRNA contains more coding regions than prokaryotic DNA. D The processing of mRNA by eukaryotes is required for the mRNA to leave the nucleus.

A 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. A 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. B Both H. arsenicoxydans and O. tritici contain the arsR gene that codes for a repressor that turns on the operon to eliminate arsenite from the cell. C Both O. tritici and E. coli contain the arsD gene, which codes for a protein that helps remove arsenite from the cell. D Both H. arsenicoxydans and O. tritici. have more arsenic resistance genes than has E. coli.

A 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. A 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. B Far-red light activates phytochrome Pr, causing it to travel to the nucleus where it binds to PIF3 at the promoter. This stimulates transcription, ultimately leading to protein production. Red light inactivates the phytochrome, which will turn transcription off by not binding to PIF3. C MYB, and not Pfr, is activated by red light, causing it to bind to the promoter and stimulate transcription and translation of cellular proteins. D PIF3 binds to the promoter only in the presence of red light and Pfr. Any time PIF3 is bound to the promoter, MYB is transcribed, initiating transcription of various other proteins in the cell.

A 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.

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? A Because nondisjunction occurred in anaphase II, all gametes will be normal and the resulting individual will be phenotypically normal. B Because nondisjunction occurred in anaphase II, all gametes will have an abnormal chromosome number and the individual will likely exhibit phenotypic evidence of the nondisjunction event. C Because nondisjunction occurred in anaphase IIII, all gametes will be normal and the resulting individual will be phenotypically normal. D Because nondisjunction occurred in anaphase IIII, all gametes will have an abnormal chromosome number and the individual will likely exhibit phenotypic evidence of the nondisjunction event.

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

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

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 RNARNA 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 ? A The presence of excess lactose blocks the functioning of RNA polymerase in this operon. B When bound to the operator, the repressor protein prevents lactose metabolism in E. coli. C The binding of the repressor protein to the operator enables E. coli to metabolize lactose. D Allolactose acts as an inducer that binds to the operator, allowing E. coli to metabolize lactose.

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

Students subjected three samples of five different molecules to gel electrophoresis as shown in Figure 1. 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? A Molecules A and B are positively charged, and molecule A is smaller than molecule B. B Molecules A and B are positively charged, and molecule A is larger than molecule B. C Molecules A and B are negatively charged, and molecule A is smaller than molecule B. D Molecules A and B are negatively charged, and molecule A is larger than molecule B.

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

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. Which of the following best explains the distribution of lactase persistence in the areas shown in Figure 1 ? A Lactase persistence developed because people were malnourished in Europe. B Lactase persistence alleles are present in all human populations and are expressed when lactose is consumed. C Mutations conferring lactase persistence likely arose independently in different geographic areas and offered a selective advantage. D The mutations that cause lactase persistence are detrimental to humans and will eventually disappear from the gene pool.

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

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? A Insertion B Deletion C Substitution D Frameshift

C Substitution

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′3′ to 5′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

C The antisense strand, because it is serving as a template

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 ? A Gene X codes for a transcription factor required for transcription of gene D. B A single transcription factor regulates transcription similarly, regardless of the specific gene. C Transcription of genes A, B, and C is necessary to transcribe gene E. D Different genes may be regulated by the same transcription factor.

D Different genes may be regulated by the same transcription factor.

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? A DNA methylation inhibits transcription of gene R. B Histone modifications of genes are usually not reversible. C Histone methylation condenses the chromatin at gene R so transcription factors cannot bind to DNA. D Histone methylation opens up chromatin at gene R so transcription factors can bind to DNA more easily.

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

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? A Gel electrophoresis can only be used with DNA (not mRNA), so experimental results are not interpretable. B RNA polymerase consistently makes the same errors during transcription of gene L. C Gene L is mutated, so RNA polymerase does not always transcribe the correct sequence. D Pre-mRNA of gene L is subject to alternative splicing, so three mRNA sequences are possible.

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

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.

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 ? A The synthesis of mRNA in the 5′5′ to 3′3′ direction from DNA B The modification of a protein to produce a functional form of that protein C The translation of an mRNA molecule into a polypeptide D The enzyme-regulated processing of pre‑mRNA into mature mRNA

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