Unit 4 Free Response Practice 1

Unit 4: Cell Communication and Cell Cycle Topic 4.1 Cell Communication 4.2 Introduction to Signal Transduction 4.3 Signal Transduction 4.4 Changes in Signal Transduction Pathways 4.5 Feedback 4.6 Cell Cycle 4.7 Regulation of Cell Cycle Learning Objective(s) IST-3.A Describe the ways that cells can communicate with one another. IST-3.B Explain how cells communicate with one another over short and long distances. IST-3.C Describe the components of a signal transduction pathway. IST-3.D Describe the role of components of a signal transduction pathway in producing a cellular response. IST-3.E Describe the role of the environment in eliciting a cellular response. IST-3.F Describe the different types of cellular responses elicited by a signal transduction pathway. IST-3.G Explain how a change in the structure of any signaling molecule affects the activity of the signaling pathway ENE-3.A Describe positive and/ or negative feedback mechanisms. ENE-3.B Explain how negative feedback helps to maintain homeostasis ENE-3.C Explain how positive feedback affects homeostasis. IST-1.B Describe the events that occur in the cell cycle. IST-1.C Explain how mitosis results in the transmission of chromosomes from one generation to the next. IST-1.D Describe the role of checkpoints in regulating the cell cycle. IST-1.E Describe the effects of disruptions to the cell cycle on the cell or organism. The binding of an extracellular ligand to a G protein-coupled receptor in the plasma membrane of a cell triggers intracellular signaling (Figure 1, A). After ligand binding, GTP replaces the GDP that is bound to Gsα , a subunit of the G protein (Figure 1, B). This causes Gsα to activate other cellular proteins, including adenylyl cyclase that converts ATP to cyclic AMP (cAMP). The cAMP activates protein kinases (Figure 1, C). In cells that line the small intestine, a cAMP -activated protein kinase causes further signaling that ultimately results in the secretion of chloride ions (Cl−) from the cells. Under normal conditions, Gsα hydrolyzes GTP to GDP, thus inactivating adenylyl cyclase and stopping the signal (Figure 1, A). Individuals infected with the bacterium Vibrio cholerae experience severe loss of water from the body (dehydration). This is due to the effects of the bacterial cholera toxin that enters intestinal cells. Scientists studied the effects of cholera toxin on four samples of isolated intestinal cell membranes containing the G protein-related signal transduction components shown in Figure 1. GTP was added to samples II and IV only; cholera toxin was added to samples III and IV only. The scientists then measured the amount of cAMP produced by the adenylyl cyclase in each sample (Table 1). (a) Describe one characteristic of a membrane that requires a channel be present for chloride ions to passively cross the membrane. Explain why the movement of chloride ions out of intestinal cells leads to water loss. (b) Identify an independent variable in the experiment. Identify a negative control in the experiment. Justify why the scientists included Sample III as a control treatment in the experiment. (c) Based on the data, describe the effect of cholera toxin on the synthesis of cAMP. Calculate the percent change in the rate of cAMP production due to the presence of cholera toxin in sample IV compared with sample II. (d) A drug is designed to bind to cholera toxin before it crosses the intestinal cell membrane. Scientists mix the drug with cholera toxin and then add this mixture and GTP to a sample of intestinal cell membranes. Predict the rate of cAMP production in pmol per mg adenylyl cyclase per min if the drug binds to all of the toxin. In a separate experiment, scientists engineer a mutant adenylyl cyclase that cannot be activated by Gsα . The scientists claim that cholera toxin will not cause excessive water loss from whole intestinal cells that contain the mutant adenylyl cyclase. Justify this claim. Polycystic kidney disease (PKD) is an inherited disease that causes water loss from the body and affects cell division in the kidneys. Because water movement across cell membranes is related to ion movement, scientists investigated the role of Na+/K+ ATPase (also known as the sodium/potassium pump) in this disease. Ouabain, a steroid hormone, binds to the Na+/K+ ATPase in plasma membranes. Individuals with PKD have a genetic mutation that results in an increased binding of ouabain to the Na+/K+ ATPase. The scientists treated normal human kidney (NHK) cells and PKD cells with increasing concentrations of ouabain and measured the number of cells (Figure 1) and the activity of the Na+/K+ ATPase (Figure 2) after a period of time. The scientists hypothesized that a signal transduction pathway that includes the protein kinases MEK and ERK (Figure 3) may play a role in PKD symptoms. (a) Describe the characteristics of the plasma membrane that prevent simple diffusion of Na+ and K+ across the membrane. Explain why ATP is required for the activity of the Na+/K+ ATPase. (b) Identify a dependent variable in the experiment represented in Figure 1. Justify the use of normal human kidney (NHK) cells as a control in the experiments. Justify the use of a range of ouabain concentrations in the experiment represented in Figure 1. (c) Based on the data shown in Figure 2, describe the relationship between the concentration of ouabain and the Na+/K+ ATPase activity both in normal human kidney (NHK) cells AND in PKD cells. The scientists determined that Na+/K+ ATPase activity in PKD cells treated with 1 pM ouabain is 150 units of ATP hydrolyzed/sec. Calculate the expected Na+/K+ ATPase activity (units/sec) in PKD cells treated with 106 pM ouabain. (d) In a third experiment, the scientists added an inhibitor of phosphorylated MEK (pMEK) to the PKD cells exposed to 104 pM ouabain. Based on Figure 3, predict the change in the relative ratio of ERK and pERK in ouabain-treated PKD cells with the inhibitor compared with ouabain-treated PKD cells without the inhibitor. Provide reasoning to justify your prediction. Using the data in Figure 1 AND the signal transduction pathway represented in Figure 3, explain how the concentration of cyclin proteins may increase in PKD cells treated with 104 pM ouabain. Acetylcholine is a neurotransmitter that can activate an action potential in a postsynaptic neuron (Figures 1 and 2). A researcher is investigating the effect of a particular neurotoxin that causes the amount of acetylcholine released from presynaptic neurons to increase. (a) Describe the immediate effect of the neurotoxin on the number of action potentials in a postsynaptic neuron. Predict whether the maximum membrane potential of the postsynaptic neuron will increase, decrease, or stay the same. (b) The researcher proposes two models, A and B, for using acetylcholinesterase (AChE), an enzyme that degrades acetylcholine, to prevent the effect of the neurotoxin. In model A, AChE is added to the synapse. In model B, AChE is added to the cytoplasm of the postsynaptic cell. Predict the effectiveness of EACH proposed model. Provide reasoning to support your predictions. Some pathogenic bacteria enter cells, replicate, and spread to other cells, causing illness in the host organism. Host cells respond to these infections in a number of ways, one of which involves activating particular enzymatic pathways (Figure 1). Cells normally produce a steady supply of inactive caspase-1 protein. In response to intracellular pathogens, the inactive caspase-1 is cleaved and forms an active caspase-1 (step 1). Active caspase-1 can cleave two other proteins. When caspase-1 cleaves an inactive interleukin (step 2), the active portion of interleukin is released from the cell. An interleukin is a signaling molecule that can activate the immune response. When caspase-1 cleaves gasdermin (step 3), the Nterminal portions of several gasdermin proteins associate in the cell membrane to form large, nonspecific pores. Researchers created the model in Figure 1 using data from cell fractionation studies. In the experiments, various parts of the cell were separated into fractions by mechanical and chemical methods. Specific proteins known to be located in different parts of the cell were used as markers to determine the location of other proteins. The table below shows the presence of known proteins in specific cellular fractions. (a) Describe the effect of inhibiting step 3 on the formation of pores AND on the release of interleukin from the cell. (b) Make a claim about how cleaving inactive caspase-1 results in activation of caspase-1. A student claims that preinfection production of inactive precursors shortens the response time of a cell to a bacterial infection. Provide ONE reason to support the student’s claim. (c) A student claims that the NF-kB protein is located in the cytoplasm until the protein is needed for transcription. Justify the student’s claim with evidence. Identify TWO fractions where N-terminal gasdermin would be found in cells infected with pathogenic bacteria. (d) Describe the most likely effect of gasdermin pore formation on water balance in the cell in a hypotonic environment. (e) Explain how gasdermin pore formation AND interleukin release contribute to an organism’s defense against a bacterial pathogen. Acetylcholine receptor (AChR) proteins are found at the synapse between neurons and skeletal muscle cells. Acetylcholine released from neurons binds to a specific site on the receptor proteins, which causes an ion channel in the receptors to open and allow sodium ions (Na+) to enter muscle cells. The resulting depolarization of muscle cells initiates muscle contractions. Another molecule, nicotine, can also bind to certain types of AChR proteins and activate the receptors. A researcher is investigating two different types of AChR proteins: type 1 and type 2. To determine which stimuli activate the receptors, the researcher exposes muscle cells expressing the different types of receptor proteins to stimuli and observes the result indicated in Table 1. (a) Describe the difference in the structure AND function between AChR type 1 and AChR type 2. (b) Acetylcholinesterase is an enzyme that breaks down acetylcholine in the synapse. Describe the effect of inhibiting acetylcholinesterase on the muscle cells with AChR type 2. The figure above represents a generalized hormone-signaling pathway. Briefly explain the role of each numbered step in regulating target gene expression. Part (a) Scoring Guidelines Topic 2.5 2.8 (b) (c) 4.2 (d) 4.2 Part (a) Topic 2.4 2.7 (b) 2.4 2.7 (c) 4.2 4.4 (d) 4.2 4.4 Part (a) Topic 4.2 (b) 4.2 Part (a) Topic 4.2 (b) 4.2 (c) 4.2 (d) 2.8 (e) 4.2 Part (a) Topic 4.4 (b) 4.4 Part Topic 4.2