MIDTERM EXAM
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 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
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
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.
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.
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 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
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.
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.
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?
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 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.
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.