unit 4 bio

A researcher observes that mice from the mutant strain experience low blood sugar. Which of the following best describes the feedback mechanism in the pathway (Figure 1) causing the low blood sugar in the mutant strain? A The positive feedback of insulin production B The negative feedback of inactive osteocalcin production C The positive feedback of the EspEsp protein D The negative feedback of insulin-secreting pancreatic cell proliferation

A

Based on the information presented, which of the following genetic changes in an individual without diabetes is most likely to result in a disrupted cellular response to insulin signaling similar to that of an individual with type 2 diabetes? A A deletion in the gene encoding the insulin receptor that removes only the cytoplasmic domain of the protein B Duplication of the gene encoding a PI-3 kinase that results in synthesis of a muscle-specific variant of the enzyme in skin cells as well as in muscle cells C A mutation in the gene encoding IRS-1 that causes the protein to be active in muscle cells even in the absence of insulin signaling D Insertion of a small segment of DNA into the promoter of the Glut4 gene that results in increased synthesis of GLUT4 proteins in muscle cells

A

Ethylene gas is an organic molecule that serves many cell signaling roles in flowering plants. Which of the following best explains how a positive feedback mechanism involving ethylene works? A Cells of ripening fruit produce ethylene, which activates the ripening response in other fruit cells. B Low water stress causes cells to produce ethylene, which binds to root cells and initiates cell division. C Cells damaged by leaf-eating insects produce ethylene, which is released into the air, and repels insects. D Fertilized ovules produce ethylene, which initiates apoptosis in flower petal cells.

A

Glycogen synthetase kinase 3 beta is a protein kinase that has been implicated in many types of cancer. Depending on the cell type, the gene for glycogen synthetase kinase 3 beta (GSK3β) can act either as an oncogene or as a tumor suppressor. Which of the following best predicts how GSK3β mutations can lead to the development of cancer? A Cells with inactive GSK3β fail to trigger apoptosis. B Cells with inactive GSK3β fail to proceed past the G2/M checkpoint. C Cells with overactive GSK3β are more likely to repair DNA damage. D Cells with overactive GSK3β have longer cell cycles.

A

The cell cycle of yeast cells grown in the nutrient-poor environment is approximately what percent of the cell cycle of yeast cells grown in the nutrient-rich environment? A 168 B 127 C 179 D 160

A

Which of the following best describes the effect of insulin binding to the receptor on the osteoblast cells? A Insulin binding ultimately increases pancreatic secretion of additional insulin. B Insulin binding blocks the release of osteocalcin from the osteoblasts. C Insulin binding inhibits the expression of EspEsp. D Insulin binding increases the pHpH of the extracellular matrix.

A

Which of the following best describes the role of mitosis in the cell cycle? A Distributing replicated chromosomes to daughter nuclei B Dividing the cytoplasm to form four gametes C Producing organelles and replicating chromosomes D Exchanging genetic material between homologous chromosomes

A

Which of the following claims is most consistent with the data shown in Figure 2 ? A EspEsp expression is necessary to prevent the overproduction of insulin. B EspEsp protein does not regulate blood-sugar levels in normal mice. C Normal mice require a higher blood concentration of insulin than mutant mice do. D Mutant mice have a cyclical pattern of insulin secretion.

A

Which of the following is a valid interpretation of the experimental results that explains how individuals with type 2 diabetes differ from individuals without diabetes? A The relatively low levels of glucose uptake in individuals with type 2 diabetes indicate that mobilization of GLUT4 to the cell surface is reduced in muscle cells of those individuals. B The relatively low levels of glucose uptake in individuals with type 2 diabetes indicate that no functional GLUT4 protein is produced in the muscle cells of those individuals. C The absence of activated insulin receptors in individuals with type 2 diabetes indicates that no insulin is secreted by the pancreatic cells of those individuals. D The absence of activated IRS-1 in individuals with type 2 diabetes indicates that no functional insulin receptor protein is produced in the muscle cells of those individuals.

A

Which of the following observations provides the best evidence that acetyl-CoA negatively regulates pyruvate dehydrogenase activity? A The rate of the pyruvate dehydrogenase-catalyzed reaction is slower in the presence of a higher concentration of acetyl-CoA. B The gene that encodes pyruvate dehydrogenase is transcribed when excess acetyl-CoA is detected. C The accumulation of acetyl-CoA stops after 70 seconds, regardless of the reaction mixture. D Acetyl-CoA is continuously broken down in the Krebs cycle.

A

Which of the following research questions is best addressed by the experiment? A How do chemical messengers affect a cell's transition between the phases of the cell cycle? B How does the number of chromosomes affect when a cell transitions to the next phase of the cell cycle? C How does the amount of genetic information change throughout the cell cycle? D How does the checkpoint at G2 serve to prevent the transmission of mutations?

A

Based on the information provided, which of the following best justifies the claim that osteocalcin is a hormone? A The phosphorylation of the insulin receptor causes a response in osteoblast bone cells. B The osteoblasts in the bone secrete osteocalcin, which causes cells in the pancreas to change their activity. C The change in expression of EspEsp changes the insulin receptor activity of the osteoblast. D The activation of the osteocalcin by a bone cell is pHpH dependent.

B

Blood vessels are surrounded by cells called smooth muscle cells. Nitric oxide triggers a signaling cascade in smooth muscle cells that causes the cells to relax (Figure 1). Which of the following is represented by the gradual increase in thickness of the arrows from the top to the bottom of Figure 1 ? A The rate at which nitric oxide triggers signaling gradually increases over time. B The number of signaling molecules that are produced or activated increases with each step in the pathway. C The size of the proteins in the pathway increases as the signaling cascade moves through the cell. D The signaling pathway uses an increase in negative feedback to reduce intracellular Ca2+Ca2+ levels and cell sensitivity to Ca2+Ca2+.

B

The diagram above represents a model of signal transduction pathways (I and II) in a cell that is targeted by two different hormones (H1 and H2). The components of the signal transduction pathways are identified in the figure legend. Each cellular molecule in both pathways can exist in an inactive or active form. When the components in pathway I are sequentially activated, the TAP molecules promote cell division. When the components in pathway II are sequentially activated, downstream signaling by the G protein is inhibited. Based on the model, which of the following mutations is most likely to result in a cell that will generate a cancerous tumor? A A mutation in the gene encoding PP that results in a nonfunctional protein B A mutation in the gene encoding G-PIP that results in a nonfunctional protein C A mutation in the gene encoding R1 so that it is inactive even in the presence of H1 D A mutation in the gene encoding R2 so that it is active even in the absence of H2

B

The mechanism of action of many common medications involves interfering with the normal pathways that cells use to respond to hormone signals. Which of the following best describes a drug interaction that directly interferes with a signal transduction pathway? A A medication causes the cell to absorb more of a particular mineral, eventually poisoning the cell. B A medication enters the target cell and inhibits an enzyme that normally synthesizes a second messenger. C A medication enters the target cell's nucleus and acts as a mutagen. D A medication interrupts the transcription of ribosomal RNA genes.

B

Trypsinogen is split by the enzyme enterokinase to form an activated molecule of the protease trypsin. Which of the following would confirm that the activation of trypsin is an example of how a positive feedback mechanism can amplify a biological process? A The activated trypsin enzyme can use enterokinase as a substrate. B The trypsin produced by the reaction is capable of splitting and activating additional trypsinogen molecules. C If levels of trypsin were to get too high, the trypsin molecules would inhibit the enzyme enterokinase. D Each mRNA molecule that codes for trypsinogen can be translated repeatedly to form many peptide molecules.

B

Which of the following best describes the data in Figure 1 ? A As the concentration of drug X increases, there is an increase in melanoma cell survival. B At a concentration above 10 μM, drug X reduces melanoma cell survival. C At a concentration below 25 μM, drug X increases survival in all melanoma cell lines. D At a concentration of 25 μM, drug X has a greater effect on melanoma line 1 than on melanoma line 2.

B

Which of the following best describes the production of DMSPDMSP by coral and coral symbionts? A A negative feedback mechanism that increases the environmental change B A negative feedback mechanism that reverses the environmental change C A positive feedback mechanism that increases the environmental change D A positive feedback mechanism that reverses the environmental change

B

Which of the following research questions would best guide an investigation of the link between the structure of the signaling molecules and the evolution of quorum sensing? A Do these molecules require the same receptors in each bacteria species to generate a response? B Did these species evolve from a common ancestor that used a similar signaling molecule? C Do these species all perform the same action when the concentration of the signaling molecules is high enough? D Did these species evolve from the same common ancestor that is still living today and uses the same receptors?

B

Which of the following statements best describes how a growth factor stimulates cell division from outside a cell? A The growth factor binds to other cells in the same area and holds them together to form a large, multicellular structure. B The growth factor binds to receptors on the cell surface, initiating a signal transduction pathway that activates specific target genes. C The growth factor binds to sugar molecules in the extracellular fluid and provides them to the cell as a source of energy. D The growth factor binds to phospholipids in the plasma membrane, creating a channel through which substances enter the cell.

B

Which of the following describes the most likely consequence of a negative feedback pathway involving the lac operon? A The breakdown products of lactose block cell division. B Diffusion of lactose across the plasma membrane would stop in the presence of lactose. C Expression of the lac operon diminishes as lactose is depleted. D Binding of DNA by the repressor would increase in the presence of lactose.

C

Which of the following best explains the most likely method by which this antitumor drug works? A Trabectedin increases the production of cyclin proteins that signal the cancer cells to enter prophase. B Trabectedin interferes with the plasma membrane, causing it to break down and expose the DNA to damage. C Trabectedin interferes with the duplication of DNA during interphase and thus prevents cancer cells from passing the G2 checkpoint. D Trabectedin interferes with the regulations of cyclin proteins, causing their levels to increase and creating errors in DNA.

C

Which of the following describes a mutation that would lead to an increase in the frequency of nondisjunction? A A mutation affecting checkpoint 1 proteins that forces cells to enter G0 B A mutation affecting checkpoint 2 proteins that allows cells to divide with DNA damage C A mutation affecting checkpoint 3 proteins that prevents attachment of spindle fibers D A mutation affecting checkpoint 2 proteins that prevents duplication of the chromosomes

C

Based on Figure 1, which of the following best explains how exercise causes blood glucose levels to rise? A Epinephrine inhibits alpha cells, causing the release of glucagon, and activates beta cells, blocking the release of insulin. B Epinephrine activates alpha cells, blocking the release of glucagon, and inhibits beta cells, causing the release of insulin. C Epinephrine activates alpha cells, causing the release of glucagon, and inhibits beta cells, blocking the release of insulin. D Epinephrine inhibits alpha cells, blocking the release of glucagon, and activates beta cells, causing the release of insulin.

C

Based on Figure 2, which of the following best supports the claim that drug X inhibits oxygen consumption? A In the absence of drug X, melanoma lines 1 and 4 consume similar amounts of oxygen. B In the presence of drug X, melanoma line 2 consumes statistically more oxygen per cell than does melanoma line 3. C Melanoma line 3 consumes statistically less oxygen per cell in the presence of drug X than it does in the presence of the solvent alone. D Melanoma line 2 in the presence of drug X consumes statistically less oxygen than does melanoma line 4 in the absence of drug X.

C

Based on the experimental results, which of the following describes the most likely defect in muscle cells of patients with type 2 diabetes? A Insulin receptor proteins do not reach the cell surface. B Insulin does not activate its receptor. C IRS-1 activation is reduced at high insulin concentrations. D GLUT4 blocks glucose from entering cells.

C

Cancer can result from a variety of different mutational events. Which of the following is LEAST likely to result in the initiation of a cancerous tumor? A A receptor mutation results in activation of a cell-division pathway in the absence of the appropriate ligand. B A mutation results in the loss of the ability to produce a tumor-suppressor protein. C A defect in a cell-cycle checkpoint prevents a cell from entering the S phase. D At the anaphase checkpoint, separation of chromatids occurs without all centromeres being attached to kinetochore microtubules from both poles.

C

One approach to treating patients with pancreatic cancer and other cancers in which the Hedgehog protein is detected is to modify the Hedgehog signaling pathway. Which of the following is the most useful approach? A Treating patients with a molecule that is structurally similar to Hedgehog and that will bind to and interact with Ptc in the same fashion as Hedgehog B Injecting patients with embryonic cells so that Hedgehog will bind to those cells instead of the cancer cells C Treating patients with a membrane-soluble compound that can bind to Smo and block its activity D Injecting patients with a preparation of purified membrane-soluble Ci that will enter the nuclei of the cancer cells and induce gene transcription

C

Which of the following best describes the scientists' findings concerning the density of symbionts presented in Figure 2 ? A The symbiont density at 32°C on day 5 was less than the density on day 0 of the experiment. B The symbiont density at 27°C on day 0 was less than the density on day 5 of the experiment. C The symbiont density at 32°C was different from the density at 27°C on days 5 and 10 of the experiment. D The symbiont density at 27°C was higher than the density at 32°C for the entire length of the experiment.

C

Which of the following patterns is shown by the data? A Mutant 1 cells are more similar to mutant 3 cells than to wild-type cells. B In wild-type cells, the percent of cells in anaphase is twice the amount of those in telophase C In mutant 3 cells, more time is spent in prophase/prometaphase than in the later stages of mitosis. D The percent of mutant 2 cells in anaphase is higher than that of mutant 1 cells.

C

Which of the following presents a correct interpretation of the changes in chromosome number depicted in Figure 1 ? A DNADNA replication occurs between metaphase and anaphase, doubling the number of chromosomes. Between telophase and cytokinesis, the cell divides in two, with each cell receiving half of the replicated chromosomes. B New chromosomes formed during prophase are doubled during anaphase and are recombined before cytokinesis. C Chromosomes enter metaphase containing two chromatids attached by a centromere. During anaphase, the chromatids are separated, each becoming a chromosome. Cytokinesis distributes the chromosomes into two separate cells. D At anaphase a cell contains two identical copies of each chromosome, but following telophase, one of the copies is broken down into nucleotides.

C

Based on the model of eukaryotic cell cycle regulation shown in the figure, which of the following best describes the effect of a drug that blocks the production of the mitotic cyclin? A The cell cycle would proceed uncontrollably, and the cell would become cancerous. B The G1 cyclin would functionally replace mitotic cyclin, and the cell would continue dividing normally. C DNA synthesis would be prevented, and the cell would stop dividing. D The cell would be prevented from entering mitosis, and the cell would stop dividing.

D

Based on the model of ferritin synthesis presented in Figure 2, which of the following describes the role of feedback on the control of intracellular iron levels? A A decrease in iron levels activates the IRP. The IRP in turn activates iron transport proteins in the cell membrane, thereby returning free iron levels to normal. B A decrease in iron levels activates synthesis of ferritin protein. Ferritin protein in turn releases bound iron, thereby returning free iron levels to normal. C An increase in iron levels activates the IRP. The IRP in turn binds iron, thereby decreasing both free iron levels and ferritin synthesis. D An increase in iron levels activates synthesis of ferritin protein. Ferritin protein in turn binds iron, thereby decreasing both free iron levels and ferritin synthesis.

D

Damaged tissue releases chemicals that activate platelets and stimulate the formation of blood clots. Which of the following predictions about the activity of platelets best describes a positive feedback mechanism? A Activated platelets release chemicals that inhibit blood clot formation. B Activated platelets release signaling molecules that inhibit cell division in damaged tissue. C Activated platelets constrict the blood vessels, stopping blood flow. D Activated platelets release chemicals that activate more platelets.

D

Figure 1 shows a model of the endocrine signaling pathway that regulates ovulation. Which of the following observations would provide evidence of a positive feedback mechanism in this system? A Estrogen from the ovaries inhibits the release of GnRH from the hypothalamus. B Progesterone from the ovaries stimulates the thickening of the uterine lining. C Progesterone from the ovaries inhibits the release of LH and FSH from the anterior pituitary. D Estrogen from the ovaries stimulates the hypothalamus and anterior pituitary to secrete more GnRH, LH, and FSH.

D

Which of the following best describes how the amount of DNA in the cell changes during M phase? A The amount of DNA doubles as the DNA is replicated. B The amount of DNA slightly increases as a result of new organelle synthesis. C The amount of DNA does not change while the cell grows. D The amount of DNA is halved as the cell divides into two daughter cells.

D

Which of the following was a positive control in the experiment? A Minutes after glucose injection B Blood insulin C Mutant strain D Normal strain

D