Unit 4 AP BIO
What is the expected percent change in the DNADNA content of a typical eukaryotic cell as it progresses through the cell cycle from the start of the G1G1 phase to the end of the G2G2 phase?
+100%
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?
168
Based on Figure 1, what percent of the time required to complete a full cycle do the cells typically spend in interphase?
95%
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 diagram below illustrates feedback control as exerted by the hormone thyroxine. What conditions would lead to increased TSH secretion? (graph of anterior pituitary/thyroid gland/hypothalamus) A) Removal of the thyroid gland, leading to a decrease in thyroxine levels due to a loss of inhibition to the hypothalamus and anterior pituitary. B) Thyroxine that was stored in the anterior pituitary prior to thyroid glad removal will signal more TSH secretion. C) Residual blood thyroxine, from prior thyroid gland removal, will bind to the cells in the anterior pituitary, signaling more TSH secretion. D) Thyroxine will remain bound to thyroxine receptors in various body cells if the thyroid gland is removed. Those body cells will secrete additional hormones that will stimulate the anterior pituitary to secrete TSH.
A
The diagram below 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 the normal intestine. Which of the following is the most plausible explanation for these findings? A) A cell surface protein on cell 4 signals cell 3 to induce the formation of the worm's intestine. B) The plasma membrane of cell 4 interacts with the plasma membrane of the posterior portion of cell 3, causing invaginations that become microvilli. C) Cell 3 passes an electrical signal to cell 4, which induces differentiation in cell 4. D) Cell 4 transfers genetic material to cell 3, which directs the development of intestinal cells.
A
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
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 defect in a cell-cycle checkpoint prevents a cell from entering the S phase.
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 receptor mutation results in activation of a cell-division pathway in the absence of the appropriate ligand. - A mutation results in the loss of the ability to produce a tumor-suppressor protein. - A defect in a cell-cycle checkpoint prevents a cell from entering the S phase. - At the anaphase checkpoint, separation of chromatids occurs without all centromeres being attached to kinetochore microtubules from both poles.
A defect in a cell-cycle checkpoint prevents a cell from entering the S phase.
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 figure below 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 change in the cytoskeletal attachment of transmembrane proteins - The presence of a large amount of the precursor form of the ligand - An increase in the ratio of the number of unsaturated to the number of saturated fatty acid tails of the membrane lipids - 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
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
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.
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.
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.
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.
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, less ADH is released, causing more water to be excreted as urine. - As tissue osmolarity rises, more ADH is released, causing more water to be excreted as urine. - As tissue osmolarity rises, less ADH is released, causing less water to be excreted as urine. - As tissue osmolarity rises, more ADH is released, causing less water to be excreted as urine.
As tissue osmolarity rises, more ADH is released, causing less water to be excreted as urine.
Researchers investigating the regulation of neurotransmitter release from presynaptic neurons proposed a model (Figure 1) in which CDK5 , a protein expressed in axon terminals, inhibits the movement of synaptic vesicles to the presynaptic membrane. To test their model, the researchers used a modified version of green fluorescent protein (GFP*) . In slightly alkaline conditions, GFP* exhibits a bright green fluorescence. In acidic conditions, GFP* exhibits no fluorescence. Using standard techniques, the gene encoding GFP* is easily introduced into living cells. By engineering the expression of GFP* in laboratory-cultured nerve cells, the researchers found that a bright green fluorescence was exhibited only when a presynaptic neuron was given a certain stimulus. Previous experiments indicate that CDK5 is active only when attached to a protein called p35 . 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? A) In the absence of any stimulus, neurons can still release neurotransmitters. B) Different neurons in the same neural network can release different amounts of neurotransmitter. C) In the depolarization phase of an action potential, postsynaptic neurons can adjust the amount of neurotransmitter bound to receptors on their surface. D) In the recovery phase following a stimulus, enzymes can be mobilized to degrade molecules present in the synaptic vesicles.
B
Which of the following describes a mutation that would lead to an increase in the frequency of nondisjunction (chromosomes fail to separate equally)? A) mutation affecting checkpoint 1 proteins that force cells to enter G0 B) A mutation affecting checkpoint 2 proteins that allow cells to divide with DNA damage C) A mutation affecting checkpoint 3 proteins that prevent attachment of spindle fibers D) A mutation affecting checkpoint 2 proteins that prevent duplication of the chromosomes
B
The graph below 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) A falling glucagon level causes a rise in the insulin level, which maintains equal amounts of both hormones in the blood. B) A high glucagon level causes a rise in the insulin level, which maintains high levels of both hormones in the blood. C) 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 is released. D) A low glucose level causes the release of insulin, which stimulates the release of more glucose from tissues, which in turn increases the amount of insulin being released.
C
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? A) PTH levels will increase, thus preventing the release of calcitonin. B) PTH levels will decline, thus stimulating the loss of calcium from bones. C) Calcitonin levels will rise, thus promoting the deposit of calcium into bones. D) Calcitonin levels will decline, thus stimulating the release of PTH.
C
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.
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)(GSK3β) can act either as an oncogene or as a tumor suppressor. Which of the following best predicts how GSK3βGSK3β mutations can lead to the development of cancer?
Cells with inactive GSK3βGSK3β fail to trigger apoptosis.
Figure 1 shows the number of chromosomes observed in an actively dividing human cell at each stage of cell division. Which of the following presents a correct interpretation of the changes in chromosome number depicted in Figure 1? A) DNA 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.
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.
Which of the following presents a correct interpretation of the changes in chromosome number depicted in Figure 1 ?
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.
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
Researchers investigating the regulation of neurotransmitter release from presynaptic neurons proposed a model (Figure 1) in which CDK5, a protein expressed in axon terminals, inhibits the movement of synaptic vesicles to the presynaptic membrane. To test their model, the researchers used a modified version of green fluorescent protein (GFP*). In slightly alkaline conditions, GFP* exhibits a bright green fluorescence. In acidic conditions, GFP* exhibits no fluorescence. Using standard techniques, the gene encoding GFP* is easily introduced into living cells. By engineering the expression of GFP* in laboratory-cultured nerve cells, the researchers found that a bright green fluorescence was exhibited only when a presynaptic neuron was given a certain stimulus. Which of the following observations best supports the hypothesis that CDK5 negatively regulates neurotransmitter release? A) Introduction of CDK5 protein into neurons results in the movement of synaptic vesicles to the plasma membrane in the absence of any stimulus. B) Uptake of a gene encoding CDK5 by neurons results in the movement of synaptic vesicles to the plasma membrane in the absence of any stimulus. C) Suppression of CDK5 expression in neurons inhibits the movement of synaptic vesicles to the plasma membrane in response to a specific stimulus. D) Inhibition of CDK5 activity in neurons increases the movement of synaptic vesicles to the plasma membrane in response to a specific stimulus.
D
Researchers performed an experiment to determine the effect of certain genetic mutations on mitosis in tropical fruit fly embryos. They determined the percentage of cells in each of four phases of mitosis as shown in Figure 1. 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) The percent of mutant 2 cells in anaphase is higher than that of mutant 1 cells. C) In wild-type cells, the percent of cells in anaphase is twice the amount of those in telophase D) In mutant 3 cells, more time is spent in prophase/prometaphase than in the later stages of mitosis.
D
Researchers investigating the regulation of neurotransmitter release from presynaptic neurons proposed a model (Figure 1) in which CDK5 , a protein expressed in axon terminals, inhibits the movement of synaptic vesicles to the presynaptic membrane. To test their model, the researchers used a modified version of green fluorescent protein (GFP*) . In slightly alkaline conditions, GFP* exhibits a bright green fluorescence. In acidic conditions, GFP* exhibits no fluorescence. Using standard techniques, the gene encoding GFP* is easily introduced into living cells. By engineering the expression of GFP* in laboratory-cultured nerve cells, the researchers found that a bright green fluorescence was exhibited only when a presynaptic neuron was given a certain stimulus. 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? - Elevated intracellular levels of p35 result in increased synaptic activity. - Degradation of p35 results in increased synaptic activity. - Reabsorption of p35 from the synaptic cleft results in increased synaptic activity. - Attachment of p35 to synaptic vesicles results in increased synaptic activity.
Degradation of p35 results in increased synaptic activity.
Scientists compared the chemical structure of several molecules that various bacterial species use for quorum sensing. Quorum sensing is an ability some bacteria have to detect the number of related cells nearby. The chemical structure of some of these molecules found in certain species of bacteria are shown in Figure 1. 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? - Do these molecules require the same receptors in each bacteria species to generate a response? - Did these species evolve from a common ancestor that used a similar signaling molecule? - Do these species all perform the same action when the concentration of the signaling molecules is high enough? - Did these species evolve from the same common ancestor that is still living today and uses the same receptors?
Did these species evolve from a common ancestor that used a similar signaling molecule?
Which of the following best describes the role of mitosis in the cell cycle?
Distributing replicated chromosomes to daughter nuclei
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.
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.
Based on Figure 1, which of the following statements best describes the epinephrine signaling pathway?
In involves enzymes activating other enzymes.
Which of the following patterns is shown by the data?
In mutant 3 cells, more time is spent in prophase/prometaphase than in the later stages of mitosis.
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 statements best describes the role of adenylyl cyclase in the epinephrine signaling pathway?
It accelerates the production of a second messenger.
In a certain signal transduction pathway, the binding of an extracellular molecule to a cell-surface protein results in a rapid increase in the concentration of cyclic AMP inside the cell. The cyclic AMP binds to and activates cytosolic enzymes that then activate other enzymes in the cell. 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.
Which of the following is true of mitosis?
It maintains the same chromosome number in the daughter cells as in the parent cell.
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.
A researcher examining a root tip observes a plant cell with condensed sister chromatids, kinetochores with attached microtubules, and individual chromosomes that are aligned at the equatorial plate of the cell. Which of the following best describes what the next process will be in the cell?
Paired chromatids will separate, and the new daughter chromosomes will move toward opposite poles of the cell.
the p53 protein regulates a cellular response to DNA damage. Based on the diagram above, which of the following best describes the role of p53 in the response to DNA damage
Phosphorylated p53 stimulates transcription of p21 , and the resulting p21 protein suppresses cell division until the DNA damage is repaired.
During mitosis, which of the following normally occurs?
Replicated chromosomes line up on the equatorial plate.
Cell communication is critical for the function of both unicellular and multicellular eukaryotes. Which of the following is likely true of cell signaling? - Cell signaling uses the highest molecular weight molecules found in living cells. - Cell signaling has largely been replaced by other cell functions in higher mammals. - Similar cell signaling pathways in diverse eukaryotes are evidence of conserved evolutionary processes. - Cell signaling functions mainly during early developmental stages.
Similar cell signaling pathways in diverse eukaryotes are evidence of conserved evolutionary processes.
The relative amount of DNA in a cell at various stages of the cell cycle is shown in Figure 1. Which of the following best describes how the amount of DNA in the cell changes during S phase? - The amount of DNA doubles as the DNA is replicated. - The amount of DNA slightly increases as a result of new organelle synthesis. - The amount of DNA does not change while the cell grows. - The amount of DNA is halved as the cell divides into two daughter cells.
The amount of DNA doubles as the DNA is replicated.
The relative amount of DNA in a cell at various stages of the cell cycle is shown in Figure 1. Which of the following best describes how the amount of DNA in the cell changes during M phase? - The amount of DNA doubles as the DNA is replicated. - The amount of DNA slightly increases as a result of new organelle synthesis. - The amount of DNA does not change while the cell grows. - The amount of DNA is halved as the cell divides into two daughter cells.
The amount of DNA is halved as the cell divides into two daughter cells.
Which of the following best describes how the amount of DNA in the cell changes during M phase?
The amount of DNA is halved as the cell divides into two daughter cells.
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? - The cell would be prevented from entering mitosis, and the cell would stop dividing. - The G1 cyclin would functionally replace mitotic cyclin, and the cell would continue dividing normally. - The cell cycle would proceed uncontrollably, and the cell would become cancerous. - DNA synthesis would be prevented, and the cell would stop dividing.
The cell would be prevented from entering mitosis, and the cell would stop dividing.
Cancer cells behave differently than normal body cells. For example, they ignore signals that tell them to stop dividing. Which of the following conditions will most likely cause a normal body cell to become a cancer cell?
The environment contains mutagens that induce mutations that affect cell-cycle regulator proteins.
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.
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 AA will no longer attach, deactivating the cellular response.
Based on the data in Figure 2, which of the following best justifies the researchers' claim that hESC-β implants can functionally replace the mouse's naturally occurring β-cells?
The mouse with an hESC-β implant successfully regulated blood glucose levels after STZ treatment but not after the implant was removed.
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 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.
Researchers studying cell cycle regulation in budding yeast have observed that a mutation in the CDC15 gene causes cell cycle arrest in telophase when the yeast cells are incubated at an elevated temperature. Which of the following statements best predicts the effect of the cell cycle arrest on proliferating yeast cells?
The yeast cells will replicate their chromosomes but will fail to complete cytokinesis.
If chemical signals in the cytoplasm control the progression of a cell to the M phase of the cell cycle, then fusion of a cell in G1 with a cell in early M phase would most likely result in the
condensation of chromatin in preparation of nuclear division in both cells
A human cell in prophase of mitosis can be distinguished from a human cell in prophase I of meiosis by the presence of
paired homologous chromosomes in the meiotic cell