Ap Bio Chapter 18 Practice Test 99 Questions with Verified Answers,100% CORRECT

Ap Bio Chapter 18 Practice Test 99 Questions with Verified Answers The role of a metabolite that controls a repressible operon is to - CORRECT ANSWER e) bind to the repressor protein and activate it The tryptophan operon is a repressible operon that is - CORRECT ANSWER E) turned off whenever tryptophan is added to the growth medium. Which of the following is a protein produced by a regulatory gene? - CORRECT ANSWER D) repressor A lack of which molecule would result in the cell's inability to "turn off" genes - CORRECT ANSWER E) corepressor Which of the following, when taken up by the cell, binds to the repressor so that the repressor no longer binds to the operator? - CORRECT ANSWER B) inducer Most repressor proteins are allosteric. Which of the following binds with the repressor to alter its conformation? - CORRECT ANSWER A) inducer A mutation that inactivates the regulatory gene of a repressible operon in an E. coli cell would result in - CORRECT ANSWER A) continuous transcription of the structural gene controlled by that regulator. The lactose operon is likely to be transcribed when - CORRECT ANSWER D) the cyclic AMP and lactose levels are both high within the cell. Transcription of the structural genes in an inducible operon - CORRECT ANSWER B) starts when the pathway's substrate is present. For a repressible operon to be transcribed, which of the following must occur? - CORRECT ANSWER C) RNA polymerase must bind to the promoter, and the repressor must be inactive. Allolactose, an isomer of lactose, is formed in small amounts from lactose. An E. coli cell is presented for the first time with the sugar lactose (containing allolactose) as a potential food source. Which of the following occurs when the lactose enters the cell? - CORRECT ANSWER B) Allolactose binds to the repressor protein Altering patterns of gene expression in prokaryotes would most likely serve the organism's survival in which of the following ways? - CORRECT ANSWER C) allowing the organism to adjust to changes in environmental conditions In response to chemical signals, prokaryotes can do which of the following? - CORRECT ANSWER B) alter the level of production of various enzymes If glucose is available in the environment of E. coli, the cell responds with a very low concentration of cAMP. When the cAMP increases in concentration, it binds to CAP. Which of the following would you expect to be a measurable effect? - CORRECT ANSWER E) increased concentrations of sugars such as arabinose in the cell In positive control of several sugar-metabolism-related operons, the catabolite activator protein (CAP) binds to DNA to stimulate transcription. What causes an increase in CAP? - CORRECT ANSWER B) decrease in glucose and increase in cAMP There is a mutation in the repressor that results in a molecule known as a super-repressor because it represses the lac operon permanently. Which of these would characterize such a mutant? - CORRECT ANSWER C) It cannot bind to the inducer. Which of the following mechanisms is (are) used to coordinate the expression of multiple, related genes in eukaryotic cells? - CORRECT ANSWER A) Genes are organized into clusters, with local chromatin structures influencing the expression of all the genes at once. If you were to observe the activity of methylated DNA, you would expect it to - CORRECT ANSWER C) have turned off or slowed down the process of transcription. Genomic imprinting, DNA methylation, and histone acetylation are all examples of - CORRECT ANSWER D) epigenetic phenomena. When DNA is compacted by histones into 10-nm and 30-nm fibers, the DNA is unable to interact with proteins required for gene expression. Therefore, to allow for these proteins to act, the chromatin must constantly alter its structure. Which processes contribute to this dynamic activity? - CORRECT ANSWER B) methylation and phosphorylation of histone tails Two potential devices that eukaryotic cells use to regulate transcription are - CORRECT ANSWER D) DNA methylation and histone modification. During DNA replication, - CORRECT ANSWER C) methylation of the DNA is maintained because methylation enzymes act at DNA sites where one strand is already methylated and thus correctly methylates daughter strands after replication. In eukaryotes, general transcription factors - CORRECT ANSWER B) bind to other proteins or to a sequence element within the promoter called the TATA box. Steroid hormones produce their effects in cells by - CORRECT ANSWER D) binding to intracellular receptors and promoting transcription of specific genes. Transcription factors in eukaryotes usually have DNA binding domains as well as other domains that are also specific for binding. In general, which of the following would you expect many of them to be able to bind? - CORRECT ANSWER D) other transcription factors Gene expression might be altered at the level of post-transcriptional processing in eukaryotes rather than prokaryotes because of which of the following? - CORRECT ANSWER C) Eukaryotic exons may be spliced in alternative patterns. Which of the following experimental procedures is most likely to hasten mRNA degradation in a eukaryotic cell? - CORRECT ANSWER B) removal of the 5' cap Which of the following is most likely to have a small protein called ubiquitin attached to it? - CORRECT ANSWER A) a cyclin that usually acts in G₁, now that the cell is in G₂ In prophase I of meiosis in female Drosophila, studies have shown that there is phosphorylation of an amino acid in the tails of histones of gametes. A mutation in flies that interferes with this process results in sterility. Which of the following is the most likely hypothesis? - CORRECT ANSWER D) Histone tail phosphorylation prohibits chromosome The phenomenon in which RNA molecules in a cell are destroyed if they have a sequence complementary to an introduced double-stranded RNA is called - CORRECT ANSWER A) RNA interference. At the beginning of this century there was a general announcement regarding the sequencing of the human genome and the genomes of many other multicellular eukaryotes. There was surprise expressed by many that the number of protein-coding sequences was much smaller than they had expected. Which of the following could account for most of the rest? - CORRECT ANSWER D) non-protein-coding DNA that is transcribed into several kinds of small RNAs with biological function Among the newly discovered small noncoding RNAs, one type reestablishes methylation patterns during gamete formation and block expression of some transposons. These are known as - CORRECT ANSWER B) piRNA. Which of the following best describes siRNA? - CORRECT ANSWER A) a short double-stranded RNA, one of whose strands can complement and inactivate a sequence of mRNA One way scientists hope to use the recent knowledge gained about noncoding RNAs lies with the possibilities for their use in medicine. Of the following scenarios for future research, which would you expect to gain most from RNAs? - CORRECT ANSWER C) targeting siRNAs to disable the expression of an allele associated with autosomal dominant disease Which of the following describes the function of an enzyme known as Dicer? - CORRECT ANSWER D) It trims small double-stranded RNAs into molecules that can block translation. In a series of experiments, the enzyme Dicer has been inactivated in cells from various vertebrates so that the centromere is abnormally formed from chromatin. Which of the following is most likely to occur? - CORRECT ANSWER C) Centromeres will be euchromatic rather than heterochromatic and the cells will soon die in culture. Since Watson and Crick described DNA in 1953, which of the following might best explain why the function of small RNAs is still being explained? - CORRECT ANSWER E) Changes in technology as well as our ability to determine how much of the DNA is expressed have now made this possible. You are given an experimental problem involving control of a gene's expression in the embryo of a particular species. One of your first questions is whether the gene's expression is controlled at the level of transcription or translation. Which of the following might best give you an answer? - CORRECT ANSWER B) You measure the quantity of the appropriate pre-mRNA in various cell types and find they are all the same. In humans, the embryonic and fetal forms of hemoglobin have a higher affinity for oxygen than that of adults. This is due to . - CORRECT ANSWER A) nonidentical genes that produce different versions of globins during development The fact that plants can be cloned from somatic cells demonstrates that - CORRECT ANSWER A) differentiated cells retain all the genes of the zygote. In animals, embryonic stem cells differ from adult stem cells in that - CORRECT ANSWER A) embryonic stem cells are totipotent, and adult stem cells are pluripotent What is considered to be the first evidence of differentiation in the cells of an embryo? - CORRECT ANSWER B) the occurrence of mRNAs for the production of tissue-specific proteins Embryonic lethal mutations result in - CORRECT ANSWER D) phenotypes that are never born/hatched Your brother has just purchased a new plastic model airplane. He places all the parts on the table in approximately the positions in which they will be located when the model is complete. His actions are analogous to which process in development? - CORRECT ANSWER E) pattern formation The product of the bicoid gene in Drosophila provides essential information about - CORRECT ANSWER E) the anterior-posterior axis. If a Drosophila female has a homozygous mutation for a maternal effect gene, - CORRECT ANSWER B) all of her offspring will show the mutant phenotype, regardless of their genotype. Mutations in which of the following genes lead to transformations in the identity of entire body parts? - CORRECT ANSWER D) homeotic genes Which of the following genes map out the basic subdivisions along the anterior-posterior axis of the Drosophila embryo? - CORRECT ANSWER B) segmentation genes Gap genes and pair-rule genes fall into which of the following categories? - CORRECT ANSWER B) segmentation genes The bicoid gene product is normally localized to the anterior end of the embryo. If large amounts of the product were injected into the posterior end as well, which of the following would occur? - CORRECT ANSWER D) Anterior structures would form in both sides of the embryo. What do gap genes, pair-rule genes, segment polarity genes, and homeotic genes all have in common? - CORRECT ANSWER A) Their products act as transcription factors. Which of the following statements describes proto-oncogenes? - CORRECT ANSWER D) They can code for proteins associated with cell growth. Which of the following is characteristic of the product of the p53 gene? - CORRECT ANSWER A) It is an activator for other genes. Tumor-suppressor genes - CORRECT ANSWER C) can encode proteins that promote DNA repair or cell-cell adhesion. BRCA1 and BRCA2 are considered to be tumor-suppressor genes because - CORRECT ANSWER B) their normal products participate in repair of DNA damage The cancer-causing forms of the Ras protein are involved in which of the following processes? - CORRECT ANSWER A) relaying a signal from a growth factor receptor Forms of the Ras protein found in tumors usually cause which of the following? - CORRECT ANSWER E) growth factor signaling to be hyperactive A genetic test to detect predisposition to cancer would likely examine the APC gene for involvement in which type(s) of cancer? - CORRECT ANSWER colorectal only In Drosophilia after ~100 minutes postfertilization, the embryo looks like the following diagram, with all nuclei having moved to the periphery and, subsequently, four of the nuclei being sequestered at the posterior end. At this point, the embryo is characterized as - CORRECT ANSWER B) nuclei in the cortex that has not undergone cytokinesis. The four sequestered cells at one end are most probably destined to become - CORRECT ANSWER B) the germ cells of the adult. Formation of the pole cells (the four sequestered cells) demonstrates the role of - CORRECT ANSWER C) maternal effect genes. The next step after the embryo is formed would be - CORRECT ANSWER D) enclosure of the nuclei in membranes, forming a single layer over the surface. Proto-oncogenes can change into oncogenes that cause cancer. Which of the following best explains the presence of these potential time bombs in eukaryotic cells? - CORRECT ANSWER B) Proto-oncogenes normally help regulate cell division. The developmental stages described for Drosophila illustrate - CORRECT ANSWER A) a hierarchy of gene expression Within a cell, the amount of protein made using a given mRNA molecule depends partly on - CORRECT ANSWER B) the rate at which the mRNA is degraded. If she moves the promoter for the lac operon to the region between the beta galactosidase gene and the permease gene, which of the following would be likely? - CORRECT ANSWER D) Beta galactosidase will be produced. 97) Which of the following statements about the DNA in one of your brain cells is true? - CORRECT ANSWER E) It is the same as the DNA in one of your heart cells. If she moves the operator to the far end of the operon (past the transacetylase gene), which of the following would likely occur when the cell is exposed to lactose? - CORRECT ANSWER D) The structural genes will be transcribed continuously. Absence of bicoid mRNA from a Drosophila egg leads to the absence of anterior larval body parts and mirror-image duplication of posterior parts. This is evidence that the product of the bicoid gene - CORRECT ANSWER C) normally leads to formation of head structures. If she moves the repressor gene (lac I), along with its promoter, to a position at some several thousand base pairs away from its normal position, which will you expect to occur? - CORRECT ANSWER E) The lac operon will function normally. What would occur if the repressor of an inducible operon were mutated so it could not bind the operator? - CORRECT ANSWER D) continuous transcription of the operon's genes If she moves the operator to a position upstream from the promoter, what would occur? - CORRECT ANSWER B) The lac operon will be expressed continuously. Which of the following is an example of post-transcriptional control of gene expression? - CORRECT ANSWER C) the removal of introns and alternative splicing of exons Which of the following is a likely explanation for the lack of transgene expression in the fifth cell line? - CORRECT ANSWER A) A transgene integrated into a heterochromatic region of the genome. Cell differentiation always involves - CORRECT ANSWER A) the production of tissue-specific proteins, such as muscle actin. Of the lines that express the transgene, one is transcribed but not translated. Which of the following is a likely explanation? - CORRECT ANSWER B) no AUG in any frame The functioning of enhancers is an example of - CORRECT ANSWER A) transcriptional control of gene expression. In one set of experiments using this procedure in Drosophila, she was readily successful in increasing phosphorylation of amino acids adjacent to methylated amino acids in histone tails. Which of the following results would she most likely see? - CORRECT ANSWER B) decreased chromatin condensation Muscle cells differ from nerve cells mainly because they - CORRECT ANSWER A) express different genes. In one set of experiments she succeeded in decreasing methylation of histone tails. Which of the following results would she most likely see? - CORRECT ANSWER A) increased chromatin condensation If a particular operon encodes enzymes for making an essential amino acid and is regulated like the trp operon, then - CORRECT ANSWER D) the amino acid acts as a corepressor. One of her colleagues suggested she try increased methylation of C nucleotides in a mammalian system. Which of the following results would she most likely see? - CORRECT ANSWER E) inactivation of the selected genes Epstein Bar Virus (EBV) causes most of us to have an episode of sore throat and swollen glands during early childhood. If we first become exposed to the virus during our teen years, however, EBV causes the syndrome we know as mononucleosis. However, in special circumstances, the same virus can be carcinogenic. What must characterize the XLP population? - CORRECT ANSWER C) They must all be males with affected female relatives. She tried decreasing the amount of methylation enzymes in the embryonic stem cells and then allowed the cells to further differentiate. Which of the following results would she most likely see? - CORRECT ANSWER C) abnormalities of mouse embryos A very rare human allele of a gene called XLP, or X-linked lymphoproliferative syndrome, causes a small number of people from many different parts of the world to get cancer following even childhood exposure to EBV. Given the previous information, what might be going on? - CORRECT ANSWER C) They must be unable to mount an immune response to EBV. In a different part of the world, namely in parts of southeast Asia, the same virus is associated with a different kind of cancer of the throat. Which of the following is most probable? - CORRECT ANSWER A) Viral infection is correlated with a different immunological reaction. In areas of the world in which malaria is endemic, notably in sub-Saharan Africa, EBV can cause Burkitt's lymphoma in children, which is usually associated with large tumors of the jaw. Which of the following is consistent with these findings? - CORRECT ANSWER D) Malarial response of the immune system prevents an individual from making EBV antibodies. A few decades ago, Knudsen and colleagues proposed a theory that, for a normal cell to become a cancer cell, a minimum of two genetic changes had to occur in that cell. Knudsen was studying retinoblastoma, a childhood cancer of the eye. One of the human leukemias, called CML (chronic myelogenous leukemia), is associated with a chromosomal translocation between chromosomes 9 and 22 in somatic cells of bone marrow. Which of the following allows CML to provide further evidence of this multistep nature of cancer? - CORRECT ANSWER C) The translocation requires breaks in both chromosomes 9 and 22, followed by fusion between the reciprocal pieces. Knudsen and colleagues also noted that persons with hereditary retinoblastoma that had been treated successfully lived on but then had a higher frequency of developing osteosarcomas (bone cancers) later in life. This provided further evidence of their theory because - CORRECT ANSWER D) one of the mutations involved in retinoblastoma is also one of the changes involved in osteosarcoma. In colorectal cancer several genes must be mutated in order to make a cell a cancer cell, supporting Knudsen's hypothesis. Which of the following kinds of genes would you expect to be mutated? - CORRECT ANSWER B) genes involved in control of the cell cycle Two children are born from the same parents. Child one inherits a predisposition to retinoblastoma (one of the mutations) and child two does not. However, both children develop the retinoblastoma. Which of the following would you expect? - CORRECT ANSWER A) an earlier age of onset in child one One hereditary disease in humans, called xeroderma pigmentosum (XP), makes homozygous individuals exceptionally susceptible to UV-induced mutation damage in the cells of exposed tissue, especially skin. Without extraordinary avoidance of sunlight exposure, patients soon succumb to numerous skin cancers. 81) Given the damage caused by UV, the kind of gene affected in those with XP is one whose product is involved with - CORRECT ANSWER C) the ability to excise single-strand damage and replace it. Which of the following best describes this phenomenon? - CORRECT ANSWER D) inherited inability to repair UV-induced mutation The researcher measures the concentration of the polypeptides from different regions in the early embryo and finds the following pattern (darker shading = greater concentration): SEE IMAGE Which of the following would be his most logical assumption? - CORRECT ANSWER D) The substance is produced in region 1 and diffuses toward region 5. A researcher has arrived at a method to prevent gene expression from Drosophila embryonic genes. The following questions assume that he is using this method. The researcher continues to study the reactions of the embryo to these new proteins and you hypothesize that he is most likely to see which of the following (while embryonic genes are still not being expressed)? - CORRECT ANSWER D) Spatial axes (anterior → posterior, etc.) begin to be determined. The researcher in question measures the amount of new polypeptide production in embryos from 2—8 hours following fertilization and the results show a steady and significant rise in polypeptide concentration over that time. The researcher concludes that - CORRECT ANSWER C) the resulting new polypeptides are due to translation of maternal mRNAs. In addition, she finds what other evidence of this single-stranded RNA piece's activity? - CORRECT ANSWER Some time later, she finds that the introduced strand separates into single-stranded RNAs, one of which is degraded. What does this enable the remaining strand to do? - CORRECT ANSWER B) bind to complementary regions of target mRNAs Within the first quarter hour, the researcher sees that the intact RNA is found in the cells. After 3 hours, she is not surprised to find that - CORRECT ANSWER A) Dicer enzyme has reduced it to smaller double-stranded pieces.