AP Bio Cell signals
A DNA mutation changes the shape of the extracellular domain of transmembrane receptor protein AA produced by the cell. Which of the following predictions is the most likely consequence of the mutation?
The molecule that normally binds to protein A will no longer attach, deactivating the cellular response.
When the concentration of GAl is highest, the average height of the control seedlings is approximately
10 cm
The concentration of all gibberellins 65 days after planting is approximately
20 ng/gram
The diagram above shows a developing worm embryo at the four-cell stage. Experiments have shown that when cell 3 divides, the anterior daughter cell gives rise to muscle and gonads and the posterior daughter cell gives rise to the intestine. However, if the cells of the embryo are separated from one another early during the four-cell stage, no intestine will form. Other experiments have shown that if cell 3 and cell 4 are recombined after the initial separation, the posterior daughter cell of cell 3 will once again give rise to normal intestine. Which of the following is the most plausible explanation for these findings?
A cell surface protein on cell 4 signals cell 3 to induce formation of the worm's intestine.
The endocrine system incorporates feedback mechanisms that maintain homeostasis. Which of the following demonstrates negative feedback by the endocrine system?
After a meal, blood glucose levels become elevated, stimulating beta cells of the pancreas to release insulin into the blood. Excess glucose is then converted to glycogen in the liver, reducing blood glucose levels.
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?
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.
The vertebrate forelimb initially develops in the embryo as a solid mass of tissue. As development progresses, the solid mass near the end of the forelimb is remodeled into individual digits. Which of the following best explains the role of apoptosis in remodeling of the forelimb?
Apoptosis involves the regulated activation of proteins in specific cells of the developing forelimb that leads to the death of those cells.
Which of the following statements best explains Delta's role in regulating cell communication through the Notch signaling pathway?
Delta restricts cell communication to short distances within a developing embryo.
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?
Did these species evolve from a common ancestor that used a similar signaling molecule?
Based on the model, which of the following best explains how regulation of neurotransmitter release might increase the range of responses to a stimulus in the nervous system?
Different neurons in the same neural network can release different amounts of neurotransmitter.
Based on Figure 1, which of the following best explains how exercise causes blood glucose levels to rise?
Epinephrine activates alpha cells, causing the release of glucagon, and inhibits beta cells, blocking the release of insulin.
Epinephrine is a protein hormone found in many animals. Epinephrine stimulates a signaling pathway that results in the breakdown of glycogen to glucose in the liver cells. Which of the following describes the initial steps in the process whereby epinephrine stimulates glycogen breakdown?
Epinephrine binds to a cell-surface receptor; the activated receptor stimulates production of the second messenger, cAMP
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?
Estrogen from the ovaries stimulates the hypothalamus and anterior pituitary to secrete more GnRH, LH, and FSH.
Ethylene is an organic compound produced by ripening fruits. In a controlled experiment, researchers found that ethylene gas stimulated the ripening process in newly harvested fruits. Which of the following describes the most likely connection between natural ethylene production and fruit ripening?
Ethylene gas is a chemical signal through which ripening fruits trigger the ripening process in other fruits.
Which of the following describes the most likely consequence of a negative feedback pathway involving the lac operon
Expression of the lac operon diminishes as lactose is depleted.
A researcher claims that the epinephrine signaling pathway controls a catabolic process in muscle cells. Which of the following statements best helps justify the researcher's claim?
Glycogen phosphorylase catalyzes the conversion of glycogen to glucose-1-phosphate.
Which of the following statements accurately uses the information presented to support the hypothesis that interruption of M function in a single body cell can result in cancer?
Growth-factor signaling can trigger mitosis in cells that are in direct contact with other cells
Based on the experimental results, which of the following describes the most likely defect in muscle cells of patients with type 2 diabetes?
IRS-1 activation is reduced at high insulin concentrations.
As shown in the diagram above, when there is low fixed nitrogen in the environment, an increase in the concentration of free calcium ions and 2-oxyglutarate stimulates the expression of genes that produce two transcription factors (NtcA and HetR) that promote the expression of genes responsible for heterocyst development. HetR also causes production of a signal, PatS, that prevents adjacent cells from developing as heterocysts. Based on your understanding of the ways in which signal transmission mediates cell function, which of the following predictions is most consistent with the information given above?
In an environment with low fixed nitrogen, treating the Anabaena cells with a calcium-binding compound should prevent heterocyst differentiation.
Based on Figure 1, which of the following statements best describes the epinephrine signaling pathway?
In involves enzymes activating other enzymes
The brain coordinates the circulatory and respiratory systems of the human body. The control of breathing, for example, involves neural pathways among the structures represented in the figure above. One important stimulus in the control of breathing is an increase in blood CO2 concentration, which is detected as a decrease in blood pH. Which of the following best describes the physiological response to an overall increase in cellular respiration in the body?
In response to low blood pH, the pH sensors send a signal to the brain, which then sends a signal to the diaphragm, resulting in an increased rate of breathing to help eliminate excess blood CO2 .
Based on the data, which of the following best represents how the mice with the implanted hESC-β cells use negative feedback to return blood glucose levels to normal if blood glucose levels increase?
Increased insulin secretion by hESC-β cells → increased glucose uptake by body cells → decreased insulin secretion by hESC-β cells
Which of the following observations best supports the hypothesis that CDK5 negatively regulates neurotransmitter release?
Inhibition of CDK5 activity in neurons increases the movement of synaptic vesicles to the plasma membrane in response to a specific stimulus.
Which of the following statements best describes the role of adenylyl cyclase in the epinephrine signaling pathway?
It accelerates the production of a second messenger.
Based on the information provided, which of the following best describes the role of insulin in this liver cell signal transduction pathway?
It acts as a ligand.
Which of the following statements best describes the role of cyclic AMP in the signal transduction pathway?
It acts as a second messenger that helps relay and amplify the signal within the cell.
Cyclic AMP phosphodiesterase is an enzyme that catalyzes the conversion of cyclic AMP to a different molecule. Which of the following best predicts the effect of inhibiting cyclic AMP phosphodiesterase in a muscle cell stimulated by epinephrine?
Phosphorylase kinase will remain active because protein kinase A will no longer be deactivated.
A student claims that the YY chromosome contains the sex-determining region gene, known as the SRYSRY gene, which causes male fetuses to develop testes. Which of the following provides correct information about cell signaling that supports the claim?
The SRY gene produces a protein that binds to specific regions of DNA in certain tissues, which affects the development of these tissues.
Based on the information provided, which of the following best justifies the claim that osteocalcin is a hormone
The osteoblasts in the bone secrete osteocalcin, which causes cells in the pancreas to change their activity.
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?
The positive feedback of insulin production
Vertebrate immune responses involve communication over short and long distances. Which of the following statements best helps explain how cell surface proteins, such as MHC proteins and T cell receptors, mediate cell communication over short distances?
The proteins interact directly with proteins on the surfaces of other cells.
Argatroban is a competitive inhibitor of thrombin. Which of the following effects on the coagulation cascade is most likely to result from inhibiting thrombin activity with argatroban?
The rate of fibrin formation will decrease.
Which of the following observations provides the best evidence that acetyl-CoACoA negatively regulates pyruvate dehydrogenase activity?
The rate of the pyruvate dehydrogenase-catalyzed reaction is slower in the presence of a higher concentration of acetyl-CoACoA.
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?
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.
Which of the following best describes the scientists' findings concerning the density of symbionts presented in Figure 2 ?
The symbiont density at 32°C was different from the density at 27°C on days 55 and 1010 of the experiment.
Which of the following best explains the feedback mechanism illustrated in Figure 1 ?
This is an example of positive feedback, because the few platelets that initially bind attract more platelets to the damaged area.
Based on the model of ferritin synthesis presented in Figure 2, which of the following best describes the mechanism whereby iron most likely regulates ferritin production?
Translation occurs under high intracellular iron concentration when the IRP-iron complex dissociates from ferritin mRNA, permitting ribosomes access to the ferritin coding region.
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?
Treating patients with a membrane-soluble compound that can bind to Smo and block its activity
The rate of pyruvic acid formation fluctuates because
the reaction is affected by negative feedback
In mammals, an increase in the concentration of sodium in the blood triggers the release of antidiuretic hormone (ADH) from the pituitary gland. As the concentration of sodium in the blood returns to previous levels, the release of ADH from the pituitary gland is reduced. Based on the information presented, which of the following describes the most likely role of ADH in maintaining blood osmolarity?
ADH promotes an increase in the movement of water into the bloodstream
Antidiuretic hormone (ADH) is important in maintaining homeostasis in mammals. ADH is released from the hypothalamus in response to high tissue osmolarity. In response to ADH, the collecting duct and distal tubule in the kidney become more permeable to water, which increases water reabsorption into the capillaries. The amount of hormone released is controlled by a negative feedback loop. Based on the model presented, which of the following statements expresses the proper relationship between osmolarity, ADH release, and urine production?
As tissue osmolarity rises, more ADH is released, causing less water to be excreted as urine
Which of the following best describes the data in Figure 1 ?
At a concentration above 10 μM10 μM, drug XX reduces melanoma cell survival.
The model shown in the figure represents the role of two hormones, calcitonin and parathyroid hormone (PTH), in maintaining normal blood calcium levels in humans. If a dietary change results in an increase in blood calcium concentration above normal levels, which of the following is the most likely effect on calcium homeostasis?
Calcitonin levels will rise, thus promoting the deposit of calcium into bones.
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?
Cells of ripening fruit produce ethylene, which activates the ripening response in other fruit cells.
Previous experiments indicate that CDK5 is active only when attached to a protein called p35. Which of the following best predicts how p35 might play a role in regulating neuron function?
Degradation of p35 results in increased synaptic activity.
Which of the following claims is most consistent with the data shown in Figure 2 ?
Esp expression is necessary to prevent the overproduction of insulin.
Which of the following best describes the effect of insulin binding to the receptor on the osteoblast cells?
Insulin binding ultimately increases pancreatic secretion of additional insulin.
Which of the following best supports the claim that ethylene initiates the signal transduction pathway that leads to ripening of fruit?
Loss-of-function mutations in ethylene receptors result in changes to the ripening process.
Which of the following was a positive control in the experiment?
Normal strain
Based on the information presented, which of the following will also occur in response to steroid signaling?
Production of a specific mRNA will increase as a result of the binding of the hormone-receptor complex to the DNA
Which of the following diagrams best represents hormone-activated gene expression?
Steroid hormone, Receptor molecule, hormone-receptor complex, Translation and Transcription
Which of the following best explains how treatment with a drug that stimulates the production of insulin receptors on target cells will affect the insulin signaling pathway in an individual with type 1 diabetes?
The drug will have little or no effect on the signaling pathway because the receptors will not be activated in the absence of insulin.
Based on the information provided, which of the following can most likely be concluded about the TSH-thyroxin loop?
The feedback mechanism would maintain relatively constant levels of thyroxin throughout tissue targets.
Which of the following statements best predicts the effect of a mutation that results in a loss of the glucocorticoid receptor's ligand binding function?
The glucocorticoid receptor will remain associated with the accessory proteins.
Which of the following outcomes will most likely result from the irreversible binding of GDP to the G protein?
The intracellular concentration of glycogen will increase.
Individuals with FH can be treated with drugs that result in increased production of LDL receptors in liver cells. Which of the following best explains the observation that the drugs can effectively control blood cholesterol levels in individuals who are heterozygous but are not effective in individuals homozygous for the mutant allele?
There must be at least one copy of the wild-type LDL receptor allele to produce functional LDL receptors.
Assuming that AAS function in the same way as naturally occurring testosterone, it is most likely that long-term abuse of AAS would
reduce sperm production
The diagram above illustrates feedback control as exerted by the hormone thyroxine. Following surgical removal of the thyroid gland, the level of TSH in the blood will increase. Which of the following best explains this increase?
A decrease in thyroxine levels means a loss of inhibition to the hypothalamus and anterior pituitary, leading to increased TSH secretion.
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 deletion in the gene encoding the insulin receptor that removes only the cytoplasmic domain of the protein
The graph above shows changes in glucagon and insulin secretions at different concentrations of blood glucose. Which of the following feedback mechanisms is best supported by the data?
A low glucose level causes the release of glucagon, which stimulates the release of more glucose from tissues, which in turn lowers the amount of glucagon being released
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 medication enters the target cell and inhibits an enzyme that normally synthesizes a second messenger.
Based on the model, which of the following mutations is most likely to result in a cell that will generate a cancerous tumor?
A mutation in the gene encoding G-PIP that results in a nonfunctional protein
The figure above shows a model of a ligand precursor being cleaved to produce an active ligand that binds to a specific receptor. Which of the following is most likely to reduce the binding of the active ligand to its receptor?
A mutation in the receptor gene that causes a substitution of a charged amino acid for a nonpolar amino acid in the ligand binding site of the receptor
Which of the following best describes the production of DMSP by coral and coral symbionts?
A negative feedback mechanism that reverses the environmental change
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
Activated platelets release chemicals that activate more platelets.
Cortisol is a hormone produced in response to stress, including starvation, in humans. Which of the following is most likely an immediate effect of a starvation-induced increase in cortisol secretion?
Increased mobilization of fatty acids from fat cells
Air is less dense at very high elevations, so less oxygen is available than in the denser air at sea level. Based on the model in Figure 1, if a person travels from sea level to a high elevation location, which of the following correctly predicts the response to the decreased blood oxygen level?
More erythropoietin will be secreted from the kidneys, increasing production of erythrocytes.
Which of the following is a correct conclusion that can be drawn from the data in Figures 1, 2, and 3?
Most of the increase in the concentration of all gibberellins 40 to 45 days after planting is due to an increase in the concentration of GAl.
Cell communication is critical for the function of both unicellular and multicellular eukaryotes. Which of the following is likely true of cell signaling?
Similar cell signaling pathways in diverse eukaryotes are evidence of conserved evolutionary processes.
In flowering plants, plasmodesmata are narrow channels through cell walls that connect the cytoplasms of adjacent cells. An explanation of how plant cells communicate across cell walls will most likely refer to the diffusion through plasmodesmata of which of the following?
Small, water-soluble molecules
Which of the following is a correct conclusion that can be drawn based only on the data in Figure 4?
The greater the inhibition of GAl synthesis, the lower the plant height after 80 days.
Which of the following statements best describes how a growth factor stimulates cell division from outside a cell?
The growth factor binds to receptors on the cell surface, initiating a signal transduction pathway that activates specific target genes.
Which of the following best explains how small molecules move between adjacent cells in a plant shoot?
The molecules pass freely through plasmodesmata, which are cytoplasmic strands connecting two cells.
In a continuation of the experiment, the researchers removed the hESC-β implant from one of the mice 16 weeks after STZ treatment. Figure 2 shows the blood glucose levels in the mouse over the duration of the experiment.
The mouse with an hESC-β implant successfully regulated blood glucose levels after STZ treatment but not after the implant was removed.
Which of the following is represented by the gradual increase in thickness of the arrows from the top to the bottom of Figure 1?
The number of signaling molecules that are produced or activated increases with each step in the pathway.
In contrast to type 1 diabetes, where there is no insulin production, type 2 diabetes is characterized by a failure of body cells to respond normally to insulin. Based on the results of the experiment, which of the following best predicts the effectiveness of using hESC-β implantation to treat type 2 diabetes?
The treatment would fail because insulin produced by implanted hESC-β cells will not stimulate glucose uptake by body cells
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
The trypsin produced by the reaction is capable of splitting and activating additional trypsinogen molecules.
Which of the following best represents two different signaling pathways that share a second messenger?
Two things come together as one then split again