BIOL 4100 Exam 3
Antimycin A is a piscicide (fish poison) used to manage fisheries and kill invasive species. Antimycin A blocks the transfer of electrons through the cytochrome b-c1 complex. What components of the electron transport chain are bound to high-energy electrons after treating a mitochondrion with antimycin A?
NADH and the NADH dehydrogenase complex are bound to high-energy electrons while O2 and the cytochrome c oxidase complex are not.
In cells, pyruvate can be converted to which of the following?
-acetyl CoA -lactate -glucose -alanine -oxaloacetate
Which membrane-enclosed organelles most likely evolved in a similar manner?
the nucleus and the ER
Three separate pathways make up the unfolded protein response in the ER. Sort the following characteristics of the unfolded protein responses into the correct pathway. All three pathways (IRE1, PERK, ATF6)
-Activates transcription of specific genes -Increases the ability of the ER to fold more proteins
Alterations in signaling in the pituitary gland can lead to human disease. The GH-releasing hormone (GHRH) stimulates release of growth hormone (GH) from the pituitary gland by binding to GHRH receptors, which are G-protein-coupled receptors. Excessive activity of the GHRH signaling pathway leads to excessive release of growth hormone, which can lead to acromegaly, a form of gigantism. Some patients can reach more than 8 feet tall as they continue to grow even in adulthood. Consider steps that could be taken to reduce GH release. Sort each of the following interventions into the proper category. Increase GH release
-Block binding of arrestin to the receptor -Block hydrolysis of GTP
Many viruses enter cells through receptor-mediated endocytosis. Which of the following strategies could be affective in blocking entry of this class of viruses into cells and could be used to treat viral infections?
-Block the receptor with an antibody. -Block the function of adaptin.
Which of the following statements correctly describe an aspect of converting light to chemical energy in chloroplasts?
-Excited electrons are passed through an electron transport chain. -The energy in excited electrons is used to pump protons across the thylakoid membrane from the stroma to the thylakoid space.
Which of the following steps are required in the activation of the G-protein signaling pathway?
-Gα exchanges GDP for GTP. -Activated Gα influences target proteins. -Ligand binds to the G-protein-coupled receptor.
Alterations in signaling in the pituitary gland can lead to human disease. The GH-releasing hormone (GHRH) stimulates release of growth hormone (GH) from the pituitary gland by binding to GHRH receptors, which are G-protein-coupled receptors. Excessive activity of the GHRH signaling pathway leads to excessive release of growth hormone, which can lead to acromegaly, a form of gigantism. Some patients can reach more than 8 feet tall as they continue to grow even in adulthood. Consider steps that could be taken to reduce GH release. Sort each of the following interventions into the proper category. Decreases GH release
-Inhibit interaction of Gα with receptor -Block ligand binding to the receptor -Activate phophorylation of the receptor by GRK kinase
Which statements are true of receptor-mediated endocytosis?
-It allows the internalization of extracellular substances in clathrin-coated vesicles. -It allows cholesterol-carrying low-density lipoproteins (LDLs) to be taken up by cells. -The process can be hijacked by viruses to gain entry into cells.
Three separate pathways make up the unfolded protein response in the ER. Sort the following characteristics of the unfolded protein responses into the correct pathway. IRE1 pathway only
-Leads to removal of an intron from a specific RNA and the translation of the mRNA -Contains both kinase and RNAse domains
What is the purpose of the 2-D fluid of the lipid bilayer?
-Movements of phospholipids within the monolayer makes a dynamic surface that 'flows' -Contributes to rapid diffusion of proteins in the membrane -Ensures membrane molecules are distributed evenly -Allows for fusion of membranes
Which molecules are required for the citric acid cycle to fully oxidize the carbons donated by acetyl CoA?
-NAD+ -GDP -oxaloacetate -O2
Which statements below accurately describe an aspect of the citric acid cycle?
-NADH is generated in steps 3, 4, and 8. -Oxaloacetate is regenerated by the end of the citric acid cycle.
Serotonin (5-hydroxytryptamine, 5-HT) is a neurotransmitter with receptors (5-HT receptors) located in cells throughout the body. There are more than a dozen different types of serotonin receptors that fall into several different classes. One class consists of serotonin-activated ion channels and the other receptor classes are G-protein-coupled receptors that associate with different G proteins. The 5-HT7A receptor couples to Gs and activates adenylyl cyclase, while the 5-HT2B receptor couples to Gq and activates phospholipase C. The diversity of receptor types has led pharmacologists to search for drugs that will bind to and modulate just a single receptor class in order to limit systemic side effects (see 5-Hydroxytryptamine Receptor Subtypes and their Modulators with Therapeutic Potentials). Place into bins the downstream effects predicted for a drug that exclusively activates the 5-HT7A receptor versus a drug that exclusively activates the 5-HT2B receptor. 5-HT7A
-PKA activation -cAMP production
Serotonin (5-hydroxytryptamine, 5-HT) is a neurotransmitter with receptors (5-HT receptors) located in cells throughout the body. There are more than a dozen different types of serotonin receptors that fall into several different classes. One class consists of serotonin-activated ion channels and the other receptor classes are G-protein-coupled receptors that associate with different G proteins. The 5-HT7A receptor couples to Gs and activates adenylyl cyclase, while the 5-HT2B receptor couples to Gq and activates phospholipase C. The diversity of receptor types has led pharmacologists to search for drugs that will bind to and modulate just a single receptor class in order to limit systemic side effects (see 5-Hydroxytryptamine Receptor Subtypes and their Modulators with Therapeutic Potentials). Place into bins the downstream effects predicted for a drug that exclusively activates the 5-HT7A receptor versus a drug that exclusively activates the 5-HT2B receptor. 5-HT2B
-PKC activation -IP3 production -Cytosolic calcium increase
In the patch-clamp technique (shown here), a small glass electrode forms a tight seal with a portion of the cell membrane (A), allowing detection of ion flow through channels (B). This technique has clinical uses. For example, some individuals with high blood pressure (hypertension) have a genetic defect in an epithelial Na+ channel (ENaC) that makes the channel hyperactive (open more than normal). Such individuals can be treated with amiloride, which inhibits sodium ion movement through ENaC. Researchers predicted that amiloride would not effectively treat hypertension in individuals with normal ENaC activity and tested this prediction by analyzing ENaC activity in patch-clamped cells from individuals with high blood pressure, some of whom showed hyperactive ENaC and some of whom showed normal ENaC activity. Which of the following results align with researcher expectations?
-Patch-clamp data showed hyperactive ENaC prior to amiloride treatment; patient benefited from amiloride. -Patch-clamp data showed normal ENaC activity prior to amiloride treatment; patient did not benefit from amiloride.
Three separate pathways make up the unfolded protein response in the ER. Sort the following characteristics of the unfolded protein responses into the correct pathway. ATF6 pathway only
-Requires cleavage of the protein -Travels to the Golgi apparatus and the nucleus before activating transcription
Protons are pumped across the mitochondrial inner membrane as electrons are transferred through the mitochondrial electron transport chain. Which of the following statements about proton pumping are correct?
-The mitochondria use the proton gradient to synthesize ATP. -The pH inside the mitochondrial matrix is higher than in the intermembrane space. -The NADH dehydrogenase, cytochrome b-c1, and cytochrome oxidase complexes all pump protons across the membrane.
The main regulatory step of glycolysis occurs in step 3. Choose all of the following that correctly describe some aspect of step 3 in glycolysis.
-The reaction generates the product fructose 1,6-bisphosphate. -The reaction is an irreversible reaction. -The enzyme that catalyzes step 3 is phosphofructokinase. -The enzyme uses an ATP.
The FRAP technique occurs in a series of steps. Select every statement that correctly describes a step in the FRAP procedure.
-The relative mobility of the fluorescently labeled molecule is measured. -The molecule of interest is fluorescently labeled.
Why must all living cells carefully regulate the fluidity of their membranes?
-to allow membranes, under appropriate conditions, to fuse with one another and mix their molecules -to ensure that membrane molecules are distributed evenly between daughter cells when a cell divides -to permit membrane lipids and proteins to diffuse from their site of synthesis to other regions of the cell
Carbohydrates on the surface of leukocytes play an important role in responding to infection or inflammation. Place the following steps of the response in the correct order.
1) Cytokines are released at sites of infection or inflammation and stimulate endothelial cells of blood vessels 2) Endothelial cells express selectins on their plasma membrane 3) Selectins bind to carbohydrates on the surface of leukocytes, causing them to stick 4) Leukocytes roll along vessel walls 5) Leukocytes crawl out of vessel into adjacent tissue
Glycolysis occurs in a series of 10 steps using 10 different enzymes. Place the following broad events that occur during glycolysis into their correct order.
1) Energy is invested by using up some ATP 2) The six-carbon sugar is split into two smaller molecules 3) Energy is captured as ATP and NADH 4) Two molecules of pyruvate are generated
Order these components involved in electron transport from those with the lowest redox potential to the highest. 1 is lowest; 5 is highest
1) NADH/NAD+ 2) NADH dehydrogenase complex 3) cytochrome c reductase 4) cytochrome c oxidase 5) H2O/O2
Put the following steps used to transport proteins into mitochondria into the proper order.
1) The mitochondrial protein is synthesized in the cytosol 2) The receptor on the mitochondrial membrane binds the signal sequence on the protein 3) The protein is delivered to the translocation apparatus on the mitochondria 4) The protein is passed through the translocation apparatus 5) The signal sequence is removed by signal peptidase and the protein folds into its final comformation
The P-type ATPase Ca2+ pump transports Ca2+ ions into the sarcoplasmic reticulum in muscle cells in a series of steps. Put the following steps into the correct order.
1) Two Ca2+ ions from the cytosol side bind to a pocket in the Ca2+ pump 2) ATP is hydrolyzed and a conserved aspartate group is phosphorylated 3) ADP is exchanged for a new ATP 4) The pump opens to the lumen side of the sarcoplasmic reticulum, releasing Ca2+ 5) Two protons bind to the pump and are exported from the sarcoplasmic reticulum
Assume five molecules of FADH2 are made in the citric acid cycle in a given amount of time. How many NADH are made during the same time interval?
15
The drug 2,4-dinitrophenol (DNP) makes the mitochondrial inner membrane permeable to H+. The resulting disruption of the proton gradient inhibits the mitochondrial production of ATP. What additional effect would DNP have on the transport of ATP out of the mitochondrial matrix?
ATP export will decrease because its carrier exploits the difference in voltage across the inner membrane.
Which of the following signaling pathways would be likely to trigger the most rapid cell response?
Acetylcholine binds to anion-channel-coupled receptor that allows Na+ to flow down its electrochemical gradient, triggering contraction of a skeletal muscle cell.
Shown is a schematic diagram of a membrane phospholipid. Which segment will always carry a negative charge? Picture: shows phospholipid; includes tail with three portions above it (A, B, C)
B (Phosphate)
Mutation in the hemoglobin gene can cause sickle-cell anemia. The defective protein found in sickle-cell anemia causes red blood cells to "sickle"—become a misshapen C shape. These misshapen cells abnormally stick to each other and can become trapped by leukocytes (white blood cells) that are rolling or paused on the endothelial cells lining the vessel. This causes blockages of small blood vessels, causing severe pain and strokes called vaso-occlusive crisis. A new drug that binds and blocks selectin proteins is in phase III clinical trials to test for improvement in patients' symptoms. Why might this be an effective treatment for vaso-occlusive crisis?
Blocking selectins would block the ability of selectin to bind leukocytes, so leukocytes would be less likely to move slowly along the vessel wall and cause a blockage of red blood cells.
How do transporters and channels select which solutes they help move across the membrane?
Channels discriminate between solutes mainly on the basis of size and electric charge; transporters bind their solutes with great specificity in the same way an enzyme binds its substrate.
Not all fat cells are equivalent. Humans and other animals contain both white fat cells and brown fat cells, named after their color. Because increases in brown fat cells may aid weight loss, researchers are interested in factors that control the ratio of white fat cells and brown fat cells, as detailed in a 2017 article in Obesity Reviews. What is the mechanism for how brown fat cells aid weight loss?
Brown fat cell mitochondria contain an uncoupling protein.
Researchers studying yeast discovered that, for some mutants, when the temperature at which the cells are grown is elevated from 25ºC to 37ºC, their secretory pathway no longer functions and the cells grow dense with unsecreted protein. When these cells are examined microscopically, they can be divided into groups that vary in terms of where the unsecreted proteins accumulate. In some of the mutants, proteins accumulate in the ER; in others, the Golgi; in others, they accumulate in vesicles near the plasma membrane. What is the likely explanation for this difference in appearance?
Different temperature-sensitive mutations affect different stages of the transport process.
When ATP and food molecules such as fatty acids are abundant, but glucose is low, which will occur?
Enzymes involved in gluconeogenesis will use energy to produce glucose.
After an overnight fast, most of the acetyl CoA entering the citric acid cycle is derived from what type of molecule?
Fatty acids
What is true of nitrogen fixation?
It reduces N2 to ammonia (NH3).
The following graphs show the number of adherent leukocytes found on the blood vessel wall in control conditions and after adding a selectin inhibitor, which blocks the function of selectin. Which of the following graphs correctly shows the effect of a selectin inhibitor on adherence of leukocytes to the vessel wall? Measuring number of adherent leukocytes; control vs. drug added Graph A: short bar, tall bar Graph B: tall bar, short bar Graph C: same height bars
Graph B
In one experiment, investigators create a liposome—a vesicle made of phospholipids—that contains a solution of 1 mM glucose and 1 mM sodium chloride. If this vesicle were placed in a beaker of distilled water, what would happen the fastest?
H2O would diffuse in.
Weight loss can occur when glucose is oxidized to CO2 rather than being stored as glycogen. The first step in glucose oxidation is glycolysis. A 1930s diet drug, DNP, made the inner mitochondrial membrane permeable to protons, increasing the rate of glycolysis. What is the explanation for the DNP-induced increase in glycolysis?
High ADP activates phosphofructokinase.
The diffusion of an integral membrane protein is studied by fluorescence recovery after photobleaching (FRAP). In this procedure, the protein of interest is labeled with a fluorescent marker, and the fluorescence in a small patch of membrane is then irreversibly "bleached" by a pulse of light from a focused laser. The time it takes for fluorescence to return to the bleached membrane patch provides a measure of how rapidly unbleached, fluorescently labeled proteins diffuse through the bilayer into the area. This "recovery" is plotted on a curve that shows fluorescence over time. For one protein, which acts as a receptor for an extracellular signal molecule, stimulation by its signal ligand causes the receptor to interact with other membrane proteins, forming a large protein signaling complex. Shown here is the FRAP result for the unstimulated receptor.
Hill decreases by a lot
You complete a further experiment by treating your cells with an RNAse inhibitor and get the results shown in Figure B. Given the results of Figure A and Figure B, what pathway(s) is/are important for this cell line? Graph 1: measuring protein folding capacity; control vs. added kinase inhibitor; tall bar vs. short bar Graph 2: measuring protein folding capacity; control vs. added RNAse inhibitor; tall bar vs. short bar
IRE1
The three pathways of the unfolded protein response differ in importance in different cell types, enabling cells to tailor the response to their individual needs. You join a lab that studies the relative importance of the UPR in different cell types. Your advisor gives you a new cell culture and directs you to determine which of the three pathways is the most important for that cell type. You first treat the cells with a kinase inhibitor. Given the results in Figure A, which pathway(s) might be important in these cells? Bar graph measuring protein folding capacity; control vs. added kinase inhibitor; tall bar vs. short bar
IRE1 and PERK
A transmembrane protein has the structure shown. Picture: transmembrane protein If an ER signal sequence were added to its N-terminus, which structure would the engineered protein adopt?
If a signal sequence were added to the protein's N-terminus (gray), this new sequence would initiate translocation. The polypeptide chain that follows this sequence would therefore be located in the ER lumen. The next hydrophobic sequence (numbered 1) would then halt translocation, and the one that follows would re-initiate translocation. This alteration would effectively turn the protein upside down; the N-terminal signal sequence would presumably be removed by a signal peptidase whose active site faces the lumenal side of the ER membrane.
A toxin present in scorpion venom prolongs the duration of action potentials in nerve cells. Which of these actions would best explain how this toxin exerts its effect?
It slows the inactivation of voltage-gated Na+ channels.
Experiments performed by Hans Krebs in the 1930s revealed that the set of reactions that oxidize food molecules and produce CO2 occur in a cycle. In one experiment, Krebs exposed pigeon muscles to malonate, a compound that inhibits succinate dehydrogenase—the enzyme that converts succinate to fumarate, indicated in red in the linear representation of the reactions of the citric acid cycle (below). Citrate -> Succinate -|> Fumarate -> Oxaloacetate Which of the following observations, made in malonate-treated muscle, led Krebs to believe that this set of reactions is cyclical?
If fumarate were added, succinate would accumulate.
When scientists were first studying the fluidity of membranes, they did an experiment using hybrid cells. Certain membrane proteins in a human cell and a mouse cell were labeled using antibodies coupled with differently colored fluorescent tags. The two cells were then coaxed into fusing, resulting in the formation of a single, double-sized hybrid cell. Using fluorescence microscopy, the scientists then tracked the distribution of the labeled proteins in the hybrid cell. Which best describes the results they saw and what they ultimately concluded?
Initially, the mouse and human proteins were confined to their own halves of the newly formed hybrid cell, but over time, the two sets of proteins became evenly intermixed over the entire cell surface. This suggests that proteins, like lipids, can move freely within the plane of the bilayer.
The drug Viagra promotes blood vessel dilation by prolonging signaling through nitric oxide (NO). How does Viagra boost NO?
It blocks the enzyme that degrades cyclic GMP.
The drug scopolamine is used to treat dizziness, motion sickness, and smooth muscle spasms. When isolated muscle cells are incubated with scopolamine, addition of acetylcholine no longer depolarizes the muscle cell membrane or stimulates muscle cell contraction. Which would best explain how scopolamine exerts its muscle-relaxing effects?
It inhibits the opening of acetylcholine-gated Na+ channels in the muscle cell membrane.
When a neuron is activated by a stimulus, its plasma membrane will change until it reaches a membrane potential of about +40 mV. What is special about this value?
It is approximately the membrane potential at which the electrochemical gradient for Na+ is zero.
What happens to the ATP produced during stage 1 of photosynthesis?
It is consumed within the chloroplast to produce glyceraldehyde 3-phosphate.
Which statement is true of glycogen phosphorylase?
It is inhibited by glucose 6-phosphate and by ATP.
What would be the consequences to NADPH production if the redox potential of pC (plastocyanin) were altered to be more negative than the redox potential of cytochrome b6-f?
NADPH production would halt since pC would no longer accept electrons from the cytochrome b6-f complex, blocking the electron transport chain.
Most sports drinks contain both carbohydrates and salts. The carbohydrates replace glucose burned during exercise and the salts replace salts lost in sweat. The salt also helps the small intestine absorb glucose. Pick the answer that accurately describes which salt is most beneficial for glucose absorption.
NaCl, because Na+ is needed for glucose entry.
Investigators introduce two proteins into the membrane of artificial lipid vesicles: (1) an ATP synthase isolated from the mitochondria of cow heart muscle, and (2) a light-activated proton pump purified from the prokaryote Halobacterium halobium. The proteins are oriented as shown in the diagram. When ADP and Pi are added to the external medium and the vesicle is exposed to light, would this system produce ATP?
No, because ATP synthase is not oriented correctly.
How does the nuclear pore restrict the passage of large molecules that do not bear the correct nuclear localization signal?
Nuclear pore proteins contain disordered segments that form a gel-like meshwork inside the pore.
To study the structure of a particular membrane protein, the target protein is usually removed from the membrane and separated from other membrane proteins. Shown below are three different proteins associated with the cell membrane. Treatment with high salt would release which protein or proteins from the bilayer?
Peripheral membrane proteins (Protein-Attached)
Three separate pathways make up the unfolded protein response in the ER. Sort the following characteristics of the unfolded protein responses into the correct pathway. PERK pathway only
Phosphorylates a translation initiation factor, leading to a global reduction in translation
Carbon fixation occurs in the second stage of photosynthesis, during the light-independent reactions of the Calvin cycle. In the first step of this cycle, the enzyme Rubisco adds CO2 to the energy-rich compound ribulose 1,5-bisphosphate, ultimately producing two molecules of 3-phosphoglycerate. In a culture of green alga that is carrying out photosynthesis in the presence of CO2 in the laboratory, what would happen to the levels of ribulose 1,5-bisphosphate and 3-phosphoglycerate in the minutes after the lights were turned off and the cultures were plunged into darkness?
Ribulose 1,5-bisphosphate would be depleted, but 3-phosphoglycerate would accumulate.
Below is a table listing the reactions that constitute the 10 steps of glycolysis, along with the change in free energy (ΔG°) for each step. Based on the data, which steps in glycolysis are effectively irreversible?
Steps 1, 3, and 10 1) glucose + ATP → glucose 6-phosphate + ADP 3) fructose 6-phosphate + ATP → fructose 1,6-bisphosphate + ADP 10) phosphoenolpyruvate + ADP → pyruvate + ATP
Investigators purify mitochondria from mammalian liver cells. They incubate these mitochondria in the absence of oxygen and the presence of succinate, an intermediate produced during the citric acid cycle. Under these conditions, succinate can donate electrons to the electron-transport chain, thereby reducing the electron carriers in the chain almost completely. When oxygen is re-introduced to this preparation, the carriers will become oxidized at different rates, as shown by the colored curves in the figure. Based on these oxidation curves, place the listed components in the order in which electrons would be passed from one to the next along the electron-transport chain. (For simplicity, the carriers are represented by the numbers 1-4.) Rate from 1-6. 1 is Electron donor; 6 is Electron acceptor
Succinate 1 2 3 4 O2
Fluorescence recovery after photobleaching (FRAP) is used to monitor the movement of fluorescently labeled molecules within the plane of a cell membrane. The molecules labeled are often proteins, but lipids can be labeled too. How would the curve that represents FRAP for labeled proteins compare to the curve representing labeled lipids?
The FRAP curve for lipids would show a much more rapid recovery to initial levels of fluorescence.
In 1925, scientists exploring how lipids are arranged within cell membranes performed a key experiment using red blood cells. Using benzene, they extracted the lipids from a purified sample of red blood cells. Because these cells have no nucleus and no internal membranes, any lipids they obtained were guaranteed to come from the plasma membrane alone. The extracted lipids were floated on the surface of a trough filled with water, where they formed a thin film. Using a movable barrier, the researchers then pushed the lipids together until the lipids formed a continuous sheet only one molecule thick. The researchers then made an observation that led them to conclude that the plasma membrane is a lipid bilayer. Which of the following would have allowed the scientists to come to this conclusion?
The extracted lipids covered twice the surface area of the intact red blood cells.
When the transport vesicle shown below fuses with the plasma membrane, which monolayer will face the cell cytosol? Picture: circle with blue on inside, orange on outside; cytosol is on the outside
The orange monolayer will face the cytosol.
ATP is important for chaperone protein function. Why would protein import into mitochondria be disrupted if ATP were depleted from inside mitochondria?
The protein could slip back out of the mitochondria during transport.
Ricin is one of the most powerful toxins known. The protein consists of two subunits: the A chain is an enzyme that inhibits translation and the B chain is a lectin that binds to carbohydrates on the cell surface. What is the most likely mechanism by which ricin enters the cell?
The protein is internalized by endocytosis.
To determine whether a signal sequence directs proteins to a particular organelle, researchers prepare two versions of the same protein: one version contains the signal sequence, while the other lacks it. They label the protein that contains the signal sequence with a radioactive marker, and then incubate both of the proteins with the organelle of interest. After allowing enough time for any of the proteins to be transported into the organelle, a protease is added to the mixture. If the signal sequence is the correct one for the selected organelle, what would the researchers likely see?
The radioactive label would be associated with an intact protein.
The signaling pathways shown below integrate information provided by signal 1 and signal 2 to activate the transcription of a target gene and trigger a cell response. The intracellular signaling molecules in the pathway are only active when they receive an activating signal (→) from an upstream signaling molecule and are not being inhibited (—I) by any upstream signaling molecule. Given this information, under what conditions will the target gene for this signaling network be expressed?
The target gene will be expressed when either signal is present on its own.
In bacteria, the transport of many nutrients, including sugars and amino acids, is driven by the electrochemical H+ gradient across the plasma membrane. In E. coli, for example, an H+-lactose symporter mediates the active transport of the sugar lactose into the cell. Given what you know about coupled transport, which is likely true of the H+-lactose symporter?
The transporter oscillates randomly between states in which it is open to either the extracellular space or the cytosol.
In a patch of animal cell membrane about 10 μm in area, which will be true?
There will be more lipids than proteins.
Your friends are on a low-fat, high-carbohydrate diet, which they claim will prevent fat accumulation within their bodies. They eat tons of pasta and bread without worrying about calorie count. What can you correctly say to your friends about their potential to accumulate lipids on their low-fat diet?
They will accumulate fats because cells can convert glycolytic metabolites into lipids.
Which membrane would show a more rapid recovery of fluorescence in a FRAP study? A. a membrane containing a large amount of cholesterol B. a membrane containing a larger proportion of saturated fatty acids C. a membrane containing equal amounts of saturated and unsaturated fatty acids D. The saturation of fatty acids in a cell membrane does not affect the speed of fluorescence recovery in a FRAP study. E. a membrane containing a larger proportion of unsaturated fatty acids
a membrane containing a larger proportion of unsaturated fatty acids
Which of the following describes the resting membrane potential of a neuron?
a state in which the flow of positive and negative ions across the plasma membrane is precisely balanced
IP3 signaling helps regulate sweating, which is important for regulating body temperature. Anhidrosis, the inability to sweat normally, can be caused by genetic and environmental factors. A rare mutation has been identified in a family with several children suffering from anhidrosis. The mutation inactivates the protein that IP3 binds on the ER membrane. Suppose cells were isolated from affected family members and exposed to different treatments. Which of the following treatments would be able to repair the signaling defect in cells isolated from these patients?
addition of high amounts of Ca2+ in the cytosol
The proton gradient that drives ATP synthesis during photosynthesis is generated by which of the following?
an electron carrier that pumps protons out of the stroma into the thylakoid space
Membrane lipids form _________ in water
bilayers
What is required for PKC activation?
binding to DAG and continuing presence of Ca2+
You join a laboratory to study muscle function. You decide to inhibit the pumping of Ca2+ into the sarcoplasmic reticulum to determine how excess cytosolic Ca2+ will affect muscle function. Which of the following strategies would be effective in blocking Ca2+ pumping?
block the phosphorylation of the conserved aspartate in the Ca2+ pump
Animals exploit the phospholipid asymmetry of their plasma membrane to distinguish between live cells and dead ones. When animal cells undergo a form of programmed cell death called apoptosis, phosphatidylserine—a phospholipid that is normally confined to the cytosolic monolayer of the plasma membrane—rapidly translocates to the extracellular, outer monolayer. The presence of phosphatidylserine on the cell surface serves as a signal that helps direct the rapid removal of the dead cell. How might a cell actively engineer this phospholipid redistribution?
by activating a scramblase and inactivating a flippase in the plasma membrane
The buildup of lactic and formic acids generated by anaerobic fermentation likely favored the evolution of which of the following?
cells that could pump protons
What is the purpose of receptors for the cell?
enable the cell to receive and process information
Intracellular condensates are non-membrane bound biochemical subcompartments that form due to phase separation among networks of weakly interacting molecules. Sabari et al., 2018, proposed that the transcriptional coactivator BRD4 helps form intracellular condensates containing other transcriptional proteins. A prediction of this proposal is that BRD4 should behave as a liquid within the condensate with rapid movement. Which procedure could be used to analyze movement of BRD2 in living cells?
fluorescence recovery after photobleaching (FRAP)
Botulism is a potentially fatal foodborne disease caused by the bacterium Clostridium botulinum. C. botulinum produces different toxins, several of which are proteases that cleave neuronal SNARE proteins. What normal process is blocked by cleavage and inhibition of SNARE proteins?
fusion of vesicles with target membranes
Membrane lipids are amphipathic, which means what?
having both hydrophobic and hydrophilic parts
Insulin is synthesized in the form of a precursor protein that requires cleavage of two different peptide segments before the mature protein is secreted from β cells in the pancreas. The first peptide is removed when the protein enters the lumen of the ER. To find out when the second cleavage event takes place, investigators prepare a pair of antibodies: one recognizes the pro-insulin precursor, the other the mature insulin protein. They tag the antibody that binds to the precursor protein with a red fluorescent marker; the antibody that binds to mature insulin is tagged with a green fluorescent marker. When both markers are present, the sample fluoresces yellow. The investigators then incubate an isolated β cell with both antibodies at the same time and monitor the fluorescence in its various membrane-bound compartments. The data are shown in the table below. Based on these observations, where is the second peptide removed from the pro-insulin precursor protein?
immature secretory vesicles The fluorescence associated with the ER and Golgi apparatus is red, which suggests that only the precursor protein is present and no appreciable cleavage has yet taken place. However, the fluorescence in mature secretory vesicles is green, indicating that by the time the protein is aggregated for secretion, cleavage is complete. The fluorescence in immature secretory vesicles is yellow, which means that both the mature protein and its precursor are present at once. (For fluorescent markers, the combination of red and green produces yellow.) Therefore, cleavage must be taking place in these immature vesicles. The absence of fluorescence in lysosomes indicates that the protein is not being routed to this compartment for processing or degradation. And the lack of fluorescence in the nucleus and mitochondria should not come as a surprise.
In an electron transport chain, electrons are passed from one transmembrane electron carrier to another, driving proton movement across a membrane (see image below). The protons then flow through ATP synthase (not shown) to generate ATP. In a 2018 article (Budin, et al., Science vol. 362) researchers probed how membrane fluidity affects electron transport chain activity and ATP production in E. coli by manipulating membrane fluidity and measuring respiration. How could researchers have increased membrane fluidity?
increase the proportion of phospholipids with unsaturated fatty acids
Which of the following components of receptor-mediated endocytosis of LDL is incorrectly matched with its function? A. clathrin: forms the coated vesicle B. LDL receptors: form bridges between the LDL particle and adaptin C. adaptin: binds to the specific receptors and recruits clathrin D. lysosome: releases LDL from the receptor
lysosome: releases LDL from the receptor
Movements of phospholipids within the monolayer does what to the surface?
makes a dynamic surface that 'flows'
Sodium ions, oxygen (O2), and glucose pass directly through lipid bilayers at dramatically different rates. Which of the following choices presents the correct order, from fastest to slowest?
oxygen, glucose, sodium ions
Membrane lipids are ________
phospholipids
In cells that cannot carry out fermentation, which products derived from glycolysis will accumulate under anaerobic conditions?
pyruvate and NADH
In a typical human secretory cell, which of the following membranes has the largest surface area?
rough ER
Cell membranes are _________ barriers
selective
Membrane alone allows ___________ permeability
selective
What makes it possible for a combination of signal molecules to evoke a response that differs from the sum of the effects that each signal could trigger on its own?
the ability of different intracellular relay systems to interact
In the absence of oxygen, in cells that cannot carry out fermentation, glycolysis would halt at which step?
the oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate
What is the purpose of channels and transporters for the cell?
they move stuff in and out
What is the purpose of adhesions and cytoskeleton for the cell?
they promote movement
The lipid bilayer is a flexible, ____________ fluid
two-dimensional
