Biol 314 Exam 2 Smartwork5 Review
Which of the following events occur in the hypothalamus of a mouse brain expressing channelrhodopsin when the blue light is switched on? A.Na+ floods into the neuron. B.Cl- floods out of the neuron. C.The neuron membrane is depolarized. D.Channelrhodopsin is activated and opened.
A.Na+ floods into the neuron. C.The neuron membrane is depolarized. D.Channelrhodopsin is activated and opened.
Which of these organelles are surrounded by a double membrane? A.nucleus B.lysosome C.mitochondrion D.peroxisome E.chloroplast F.Golgi apparatus
A.nucleus C.mitochondrion E.chloroplast
When an action potential reaches a nerve terminal, what type of voltage-gated channels are opened and result in the fusion of synaptic vesicles with the cell membrane? Na+ Ca2+ K+ Cl-
Ca2+
Which of the following ions has a low cytosolic concentration so that a flood of this ion into the cell can be used as a signal for cell processes like fertilization? Ca2+ H+ phosphate K+
Ca2+
Shown is a diagram of a nerve cell. Which line indicates the location of the dendrites? 2 3 1 4
2 (the little arms branching out of the nucleus)
A symport protein would function as an antiport protein if its orientation in the membrane were reversed. T/F
False
An electrical signal can jump across the synaptic cleft between the presynaptic and postsynaptic cells. T/F
False
Which organelle is essentially a small sac of digestive enzymes that functions in degrading worn-out organelles, as well as macromolecules and particles taken into the cell by endocytosis? nucleus lysosome Golgi apparatus endosome peroxisome
lysosome
What is the voltage difference across a membrane of a cell called? potential balance gradient establishment membrane potential electrical current
membrane potential
Which organelle receives proteins and lipids from the endoplasmic reticulum, modifies them, and then dispatches them to other destinations in the cell? nucleus Golgi apparatus peroxisome mitochondrion endosome
Golgi apparatus
In fungi, plants, and bacteria, which pump helps to drive the import of solutes? Ca2+ pumps Na+ pumps H+ pumps K+ pumps ATP pumps
H+ pumps
Which statement is true of the ER signal sequence on soluble proteins? It will be cleaved from the polypeptide before translocation begins. When it is found at the C-terminus of the protein, it will remain in the cytosol. It will function to open the protein translocator. When it is located in the middle of the polypeptide, it will remain part of the mature protein. It will be cleaved from the polypeptide but remain embedded in the ER membrane.
It will function to open the protein translocator.
In most animal cells, which ion can move through "leak" channels? Ca2+ Na+ Cl- H+ K+
K+
Oligosaccharide chains added in the ER can undergo further modification in which organelle(s)? only the cis Golgi network lysosomes both the cis and trans Golgi networks endosomes only the trans Golgi network
both the cis and trans Golgi networks
What protein can assemble into a basketlike network that gives budding vesicles their shape? SNARE clathrin Rab protein dynamin adaptin
clathrin
Approximately what percentage of the volume of a typical eukaryotic cell is comprised of cytosol? 80% 10% 20% 50%
50%
Which is true of ribosomes? A special class of ribosomes attached to the ER membrane translates the proteins destined for that organelle. All ribosomes are attached to the ER when they begin synthesizing a protein. Polyribosomes translate only those proteins that have an ER signal sequence. A common pool of ribosomes is used to synthesize both cytosolic proteins and proteins destined for the ER. Polyribosomes translate only cytosolic proteins.
A common pool of ribosomes is used to synthesize both cytosolic proteins and proteins destined for the ER.
How does an action potential spread along the cell membrane? A. A change in membrane potential triggers the opening of nearby voltage-gated sodium channels in a one-way direction. B. The ions entering the cell upon triggering an action potential travel laterally along the membrane to carry the charge. C. Voltage-gated Ca2+ channels are activated by the action potential and the calcium diffuses along the membrane. D. Potassium leak channels quickly reverse the action potential to move the membrane depolarization away from the original site.
A. A change in membrane potential triggers the opening of nearby voltage-gated sodium channels in a one-way direction.
Why would a cell express the aquaporin protein if water can cross the membrane in the absence of aquaporin? A. Aquaporin facilitates the faster movement of water molecules across the membrane. B. Water molecules cannot cross the membrane in the absence of a pore like aquaporin. C. Aquaporin moves a positively charged ion along with water across the membrane. D. Aquaporin limits the movement of water molecules so they do not move too quickly across the membrane.
A. Aquaporin facilitates the faster movement of water molecules across the membrane.
How do transporters and channels select which solutes they help move across the membrane? A. 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. B. Both channels and transporters discriminate between solutes mainly on the basis of size and electric charge. C. Channels allow the passage of solutes that are electrically charged; transporters facilitate the passage of molecules that are uncharged. D. Transporters discriminate between solutes mainly on the basis of size and electric charge; channels bind their solutes with great specificity in the same way an enzyme binds its substrate. E. Channels will allow the passage of any solute as long as it has an electrical charge; transporters bind their solutes with great specificity in the same way an enzyme binds its substrate.
A. 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.
Which of the following is a difference between exocytic and endocytic pathways? A. Exocytic pathways often start with synthesis of proteins, whereas endocytic pathways involve breaking down macromolecules like proteins. B. Endocytic pathways transfer proteins to the Golgi apparatus, whereas exocytic pathways transfer proteins from the Golgi. C. Exocytic pathways utilize transport vesicles, whereas endocytic pathways use only endosomes. D. Endocytic pathways bring in soluble proteins only, whereas exocytic pathways move both soluble proteins and membrane-bound proteins.
A. Exocytic pathways often start with synthesis of proteins, whereas endocytic pathways involve breaking down macromolecules like proteins.
The glucose-Na+ symport transports glucose into the epithelial cells lining the gut. How would import of glucose into the cells be affected by addition of a leaky Na+ channel to their plasma membrane? A. Glucose transport would slow because the Na+ gradient is dissipated by the Na+ channel. B. Na+ transport would slow, but glucose transport would remain high because glucose could still be transported by the glucose-Na+ symport. C. Glucose transport would increase because the Na+ gradient is strengthened by the Na+ channel. D. A leaky Na+ channel would not affect glucose transport because these two transporters are unrelated.
A. Glucose transport would slow because the Na+ gradient is dissipated by the Na+ channel.
When Na+ channels are opened in an animal cell, what happens to the membrane potential? A. It becomes less negative inside the cell. B. It rapidly reaches the resting membrane potential. C. It disappears, and membrane potential stabilizes at 0 mV. D. It stays the same. E. It becomes more negative inside the cell.
A. It becomes less negative inside the cell.
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. A. NaCl, because Na+ is needed for glucose entry. B. HCl, because H+ is needed for glucose entry. C. KCl, because K+ is needed for glucose entry. D. KCl, because Cl- is needed for glucose entry.
A. NaCl, because Na+ is needed for glucose entry.
Why does optogenetics hold the potential to help scientists better understand neurobiology? A. Optogenetics can be used to analyze neural circuits and complex behavior. B. Optogenetics can be used to visualize how neurons contact other cells. C. Optogenetics can be used to study how Na+ channels transport Na+. D. Optogenetics can help us understand how light stimulates neurons in the brain.
A. Optogenetics can be used to analyze neural circuits and complex behavior.
In the technique called optogenetics, light-gated Na+ channels are introduced into the brains of living animals. Activation of these channels by light can depolarize the membranes of neurons that contain them, selectively activating these target cells. Since its inception, optogenetics has been expanded to include other types of light-gated channels, such as a channel that is selective for Cl- instead of Na+. If this light-gated Cl- channel were introduced into neurons in a region of the brain that stimulates feeding, what might you expect to see? A. The animals would avoid eating, even when they are hungry—but only when the channels are activated by light. B. In response to light activation, the animals would overeat, even when they are full. C. The channels would have no effect on behavior because the animal's normal Na+ channels would allow normal depolarization of neurons that regulate feeding. D. The animals would avoid eating, but only during the day. E. The animals would avoid eating, even when they are hungry.
A. The animals would avoid eating, even when they are hungry—but only when the channels are activated by light.
The epithelial cells that line the gut have glucose-Na+ symport proteins that actively take up glucose from the lumen of the gut after a meal, creating a high glucose concentration in the cytosol. How do these cells release that glucose for use by other tissues in the body? A. The cells have glucose uniports in their plasma membrane. B. Glucose diffuses down its concentration gradient through the lipid bilayer of the plasma membrane. C. The cells have glucose channels in their plasma membrane. D. The cells have a glucose pump that expels the glucose needed by other tissues. E. The cells run the glucose-Na+ symport proteins in reverse.
A. The cells have glucose uniports in their plasma membrane.
Tetrodotoxin is a potent toxin found in a variety of organisms including the pufferfish. The toxin binds to the extracellular side of the Na+ channel and prevents channel opening. This leads to paralysis of muscles, including the diaphragm. Death from respiratory failure can occur after ingestion of as little as 1 mg of the toxin. Why does this toxin cause paralysis? A. The membrane depolarization is not amplified along the axon. B. The Na+ channel does not open wide enough to allow enough Na+ through the channel. C. The axon membranes become over-depolarized. D. The Na+ channels remain in the inactive, refractory state.
A. The membrane depolarization is not amplified along the axon.
Your friend now has the pumps successfully pumping ions. She added an equal concentration of both ions to the correct sides of the liposomes along with an excess of the energy source. She is surprised when the pumps stop working after a short time. Which of the following could explain why the transporter stopped pumping ions? A. The pump ran out of Na+ to pump because it pumps 3 Na+ out for every 2 K+ pumped in. B. The liposomes ran out of pumps to pump ions. C. The pump ran out of K+ to pump because it pumps 3 K+ out for every 2 Na+ pumped in. D. The pump ran out of both Na+ and K+ because an equal number of both ions is pumped in each cycle.
A. The pump ran out of Na+ to pump because it pumps 3 Na+ out for every 2 K+ pumped in.
What is the role of K+-gated ion channels in an action potential? A. They help reverse the action potential by repolarizing the cell. B. They provide the energy for the sodium-potassium pump to reestablish resting potential. C. They do not have a role in action potentials. D. They lead to the action potential reaching its highest state of cell depolarization.
A. They help reverse the action potential by repolarizing the cell.
How is an electrical signal converted to a chemical signal at a nerve terminal? A. Voltage-gated Ca2+ channels are activated and the influx of Ca2+ triggers the release of neurotransmitters. B. The influx of ions leads to a pH change, chemical transformation, and signaling. C. Mechanically gated channels change conformation due to the electrical signal and create a mechanical signal. D. Ligand-gated channels are bound by ions and open to allow the flow of neurotransmitters out of the cell.
A. Voltage-gated Ca2+ channels are activated and the influx of Ca2+ triggers the release of neurotransmitters.
An electrochemical gradient has a chemical component and an electrical component. Which of the following will have the largest electrochemical gradient? A. a positively charged ion, such as Na+, at high concentrations outside the cell B. a positively charged ion, such as K+, at high concentrations inside the cell C. a negatively charged ion, such as Cl-, at high concentrations outside the cell
A. a positively charged ion, such as Na+, at high concentrations outside the cell
Which of the following describes the resting membrane potential of a neuron? A. a state in which the flow of positive and negative ions across the plasma membrane is precisely balanced B. a voltage difference of 0 millivolts (mV) across the membrane C. a voltage difference across the plasma membrane when the neuron has been stimulated D. a voltage difference that is chiefly a reflection of the electrochemical Na+ gradient across the plasma membrane E. a voltage difference across the plasma membrane, with more positive membrane potential inside
A. a state in which the flow of positive and negative ions across the plasma membrane is precisely balanced
Curare is a chemical purified from the bark of a South American vine, Chondrodendron tomentosum. South American native hunters place the curare on arrow tips. Animals shot with these arrows die from respiratory failure. Derivatives of curare have also been developed for medical use as a muscle relaxant that causes paralysis of muscles during surgery or other procedures. In this case, the muscle cell is the postsynaptic cell. Which of the following potential drug mechanisms would fit with the main outcome of muscle paralysis? A. competitive inhibitor of the ligand-gated ion channel on the postsynaptic cell B. agonist that leads to opening of the Ca2+ channel on the presynaptic cell C. competitive inhibitor of neurotransmitter reuptake by the presynaptic cell D. All three of these mechanisms could potentially cause muscle paralysis.
A. competitive inhibitor of the ligand-gated ion channel on the postsynaptic cell
What is the conformation of the voltage-gated Na+ channel that keeps the action potential from traveling backward along the axonal membrane? A. inactivated B. triggered C. open D. closed
A. inactivated
Which of the following components of receptor-mediated endocytosis of LDL is incorrectly matched with its function? A. lysosome: releases LDL from the receptor B. clathrin: forms the coated vesicle C. adaptin: binds to the specific receptors and recruits clathrin D. LDL receptors: form bridges between the LDL particle and adaptin
A. lysosome: releases LDL from the receptor
A group of researchers wanted to sort different white blood cell types (monocytes, lymphocytes, and granulocytes) apart from each other based on size differences and to remove unwanted contaminating red blood cells. After a particular manipulation, the red blood cells lysed. The remaining white blood cells increased in size and, more importantly, the size differences among cells increased, allowing for size-based sorting (which requires minimum size differences among cells). What manipulation did the researchers use to increase cell size? A. placing cells in an environment with a lower solute concentration than that in the cells B. patch-clamp recording to monitor ion channel activity C. placing cells in an environment with a higher solute concentration than that in the cells D. placing cells in an environment with lower temperatures than the cells were previously exposed to
A. placing cells in an environment with a lower solute concentration than that in the cells
Which of the following activities helps restore the ion gradients across the plasma membrane of an axon after an action potential has occurred? A. the action of Na+ pumps B. the opening of voltage-gated Na+ channels C. the activity of K+ leak channels D. the closing of voltage-gated K+ channels
A. the action of Na+ pumps
Which type of membrane transport protein can perform either passive or active transport? A. transporters B. Neither type of membrane transport protein can perform both passive and active transport. C. channels D. both channels and transporters
A. transporters
Which of the following is supported by the information in the figure? A.Nucleotides enter the cell by facilitated diffusion. B.Sodium and potassium are involved in co-transport. C.Glucose enters the cell by simple diffusion.
A.Nucleotides enter the cell by facilitated diffusion. B.Sodium and potassium are involved in co-transport.
Intracellular Ca2+ levels are important in cardiac muscle. Increasing intracellular Ca2+ levels in heart muscle cells leads to an increase in muscle contraction. Lowering the intracellular Ca2+ levels decreases the strength of cardiac muscle contraction. Congestive heart failure can occur when the heart's pumping of blood is weaker than normal, which leads to fluid collecting around organs, including the heart. One treatment method is to give the patient drugs that increase the strength of the heart muscle contraction. Which of the following might function as an effective treatment of congestive heart failure by increasing the strength of heart muscle contraction? A.a drug that inhibits the Na+-K+ pump from establishing a strong Na+ gradient B.a drug that blocks the calcium channel in heart muscle cells C.a drug that decreases the activity of the Na+/Ca2+ transporter D.a diuretic drug that triggers removal of excess Na+ from the body
A.a drug that inhibits the Na+-K+ pump from establishing a strong Na+ gradient C.a drug that decreases the activity of the Na+/Ca2+ transporter D.a diuretic drug that triggers removal of excess Na+ from the body
Which of the following pathways can deliver materials directly to lysosomes? A.pinocytosis B.exocytosis C.endocytosis D.autophagy E.phagocytosis
A.pinocytosis C.endocytosis D.autophagy E.phagocytosis
Which of the following is true of lysosomes? The products of digestion in lysosomes leave the lysosome by transport vesicles. Most of the lysosomal membrane proteins have glycosylated regions on the cytosolic side of the membrane. Lysosomes contain around 40 types of hydrolytic enzymes, which are optimally active at pH 7.2.4. Lysosomes have a pH that is higher than that of the cytosol. An ATP-driven H+ pump in the lysosomal membrane maintains the organelle's pH.
An ATP-driven H+ pump in the lysosomal membrane maintains the organelle's pH.
Identify chemicals that will diffuse through the lipid bilayer based on the comparison pattern that is established by the figure. Drag the labels to their targets. Target order: Small, nonpolar molecules Small, uncharged polar molecules Larger uncharged polar molecules Ions A Glucose B O2 C Na+ D H2O
B O2 D H2O A Glucose C Na+
Which of the following statements is true about the concentration of calcium ions in cells? A. Calcium levels are kept the same in the cytosol compared to outside the cell. B. Calcium levels are kept low in the cytosol compared to outside the cell. C. Calcium levels are kept high in the cytosol compared to outside the cell.
B. Calcium levels are kept low in the cytosol compared to outside the cell.
How are misfolded proteins and incompletely assembled proteins retained in the ER? A. The misfolded proteins are immediately sent to lysosomes. B. Chaperone proteins bind them and prevent their entry into vesicles. C. Misfolded proteins can exit the ER but are immediately returned by a KDEL sequence. D. Incompletely assembled proteins aggregate into large complexes that are degraded in the ER.
B. Chaperone proteins bind them and prevent their entry into vesicles.
During the activation of a neuron, the action potential propagates in only one direction. How is this achieved in the neuron? A. The Na+ channel remains open during the action potential and then rapidly returns to the closed state after the action potential passes. B. The Na+ channel becomes inactivated and refractory to reopening for a short time after the action potential passes. C. The Na+ channel closes during the action potential and then rapidly returns to the open state after the action potential passes. D. The Na+ channel becomes permanently inactivated after the action potential passes.
B. The Na+ channel becomes inactivated and refractory to reopening for a short time after the action potential passes.
Which of the following requires an input of energy to occur? A. the movement of a solute from a region of higher concentration on one side of a membrane to a region of lower concentration on the other side B. The movement of a solute from a region of lower concentration on one side of a membrane to a region of higher concentration on the other side C. Both of these options require energy investment because diffusion is a change in a system, and any change requires energy.
B. The movement of a solute from a region of lower concentration on one side of a membrane to a region of higher concentration on the other side
Each of these mechanisms of transport, as illustrated above, is best categorized by which term? A. facilitated diffusion B. active transport C. simple diffusion D. osmosis
B. active transport
Cardiac muscle cells contain a Na+/Ca2+ transporter responsible for maintaining a low cytosolic Ca2+ concentration, which helps regulate cardiac muscle contraction. Ca2+ is transported out of the cell as Na+ is brought into the cell. What type of transporter is this protein? A. symport B. antiport C. channel D. uniport
B. antiport
Why do cells lack membrane transport proteins that are specific for the movement of O2? A. because oxygen is transported in and out of the cell by special oxygen-binding proteins such as hemoglobin B. because oxygen dissolves readily in lipid bilayers C. because oxygen concentrations must be kept low inside cells to avoid creating reactive superoxide radicals that can damage DNA and proteins D. because oxygen, dissolved in water, can enter cells via aquaporins E. because transport of oxygen across cell membranes is energetically unfavorable
B. because oxygen dissolves readily in lipid bilayers
Prozac, a common antidepressant medication, functions by altering neurotransmitter levels in the brain. How does Prozac work? A. by making serotonin-gated channels easier to open B. by blocking the reuptake of serotonin after it has been released, increasing the amount available in the synapses that use it C. by increasing the amount of serotonin released from the presynaptic neuron, increasing the amount available in the synapses that use it D. by decreasing the amount of serotonin released from the presynaptic neuron, decreasing the amount available in the synapses that use it
B. by blocking the reuptake of serotonin after it has been released, increasing the amount available in the synapses that use it
Which of the following inhibits inorganic ions, such as Na+ and Cl-, from passing through a lipid bilayer? A. the watery environment on either side of the lipid bilayer B. the hydrophobic interior of the lipid bilayer C. the hydrophilic exterior of the lipid bilayer D. the carbohydrate layer on the surface of the lipid bilayer E. the ions' large size
B. the hydrophobic interior of the lipid bilayer
Which of the following correctly describes osmosis? A. the movement of water from an area of high solute concentration to an area of low solute concentration B. the movement of water from an area of low solute concentration to an area of high solute concentration C. the movement of water from an area of low water concentration to an area of high water concentration D. the movement of water from an area of low solvent concentration to an area of high solvent concentration
B. the movement of water from an area of low solute concentration to an area of high solute concentration
During an action potential, which of the following actions does not help return the membrane to its resting potential? A. the flow of K+ through K+ leak channels B. the opening of voltage-gated Na+ channels C. the inactivation of voltage-gated Na+ channels D. the opening of voltage-gated K+ channels
B. the opening of voltage-gated Na+ channels
Which of the following mechanisms prevents osmotic swelling in plant cells? A. turgor pressure B. tough cell walls C. the collection of water in contractile vacuoles D. the expulsion of water from contractile vacuoles E. the activity of Na+ pumps
B. tough cell walls
In which process do Rab proteins function? A. cargo protein delivery B. vesicle tethering C. vesicle docking D. vesicle fusion
B. vesicle tethering
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? A.Increase the activity of clathrin. B.Block the receptor with an antibody. C.Block the actin filaments. D.Block the function of adaptin.
B.Block the receptor with an antibody. D.Block the function of adaptin.
Given the type of transporter as determined in Part 1, choose all of the correct statements below that relate to the function of the Na+/Ca2+ transporter. A.The transporter directly uses ATP as an energy source for transporting ions. B.The transporter uses the Na+ electrochemical gradient as an energy source for transporting ions. C.Na+ is transported against its electrochemical gradient. D.Ca2+ is transported against its electrochemical gradient.
B.The transporter uses the Na+ electrochemical gradient as an energy source for transporting ions. D.Ca2+ is transported against its electrochemical gradient.
Which of the following organelles is the site of steroid hormone synthesis in endocrine cells? A. cytosol B. nucleus C. smooth endoplasmic reticulum D. mitochondrion
C. smooth endoplasmic reticulum
Where in the cell are some proteins initially decorated with an oligosaccharide tree on asparagine residues? peroxisome cytosol ER nucleus Golgi apparatus
ER
Which of the following organelles is surrounded by a single membrane? A. chloroplasts B. nucleus C. Golgi apparatus D. mitochondria
C. Golgi apparatus
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? A. It inhibits the transporters that pump Ca2+ into the muscle cell cytosol during an action potential. B. It inhibits the opening of Ca2+ channels in the sarcoplasmic reticulum. C. It inhibits the opening of acetylcholine-gated Na+ channels in the muscle cell membrane. D. It inhibits the transporters that pump Na+ into the muscle cell cytosol during an action potential. E. It inhibits the opening of voltage-gated K+ channels.
C. It inhibits the opening of acetylcholine-gated Na+ channels in the muscle cell membrane.
Which of the following accurately describes the role of the Na+-K+ pump? A. It maintains a lower Na+ concentration outside the cell. B. It maintains a higher K+ concentration outside the cell. C. It maintains a higher Na+ concentration outside the cell. D. It equilibrates the concentrations of Na+ and K+ across the plasma membrane.
C. It maintains a higher Na+ concentration outside the cell.
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? A. It inhibits the opening of voltage-gated Na+ channels. B. It prolongs the inactivation of voltage-gated Na+ channels. C. It slows the inactivation of voltage-gated Na+ channels. D. It slows the inactivation of voltage-gated K+ channels. E. It accelerates the opening of voltage-gated K+ channels.
C. It slows the inactivation of voltage-gated Na+ channels.
Which of the following statements is not true regarding active transport by transmembrane pumps? A. Some solutes are moved across a membrane against their concentration gradient using energy from sunlight. B. Some solutes are moved against their concentration gradients, from one side of a membrane to the other, using energy from ATP hydrolysis. C. Some solutes are transported across the membrane in tandem with other molecules, both moving from lower concentration to higher concentration.
C. Some solutes are transported across the membrane in tandem with other molecules, both moving from lower concentration to higher concentration.
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? A. Lactose and H+ ions bind to two different conformations of the transporter. B. To undergo the conformational change that releases lactose into the cell, the transporter hydrolyzes ATP. C. The transporter oscillates randomly between states in which it is open to either the extracellular space or the cytosol. D. The transporter goes through an intermediate state in which the lactose-binding site is open to both sides of the membrane. E. If the H+ gradient were reversed, the transporter could serve as an H+-lactose antiport.
C. The transporter oscillates randomly between states in which it is open to either the extracellular space or the cytosol.
What is typically true of ion channels? A. They are nonselective. B. They operate by active transport. C. They are gated. D. They hydrolyze ATP. E. They are open all the time.
C. They are gated.
In general, which of the following will diffuse across a lipid bilayer most rapidly? A. water B. a large hydrophilic molecule C. a small hydrophobic molecule D. a small hydrophilic molecule E. a large hydrophobic molecule
C. a small hydrophobic molecule
How do the interiors of the ER, Golgi apparatus, endosomes, and lysosomes communicate with each other? A. by excreting hormones and other small signaling molecules B. by open pores that allow ions to exit and enter the organelles C. by small vesicles that bud off of one organelle and fuse with another D. They do not communicate with one another. E. by fusing with one another
C. by small vesicles that bud off of one organelle and fuse with another
The outer membrane of the nucleus is continuous with the membrane of which other organelle? A. endosome B. Golgi apparatus C. endoplasmic reticulum D. mitochondrion E. peroxisome
C. endoplasmic reticulum
Which organelle is important for controlling the concentration of calcium ions in the cytosol? A. Golgi apparatus B. nucleus C. endoplasmic reticulum D. lysosome
C. endoplasmic reticulum
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? A. glucose, oxygen, sodium ions B. glucose, sodium ions, oxygen C. oxygen, glucose, sodium ions D. oxygen, sodium ions, glucose E. sodium ions, oxygen, glucose
C. oxygen, glucose, sodium ions
Which of the following characteristics of aquaporins ensure that the channel selectively transports only water molecules and not other solutes? A.The channel undergoes conformational changes to push water through the channel. B.A glutamate at the entrance to the channel prevents positive ions from entering the channel. C.The channel has a narrow pore that is only wide enough for a single water molecule to pass through. D.Two asparagines in the center of the pore prevent protons from passing through the channel.
C.The channel has a narrow pore that is only wide enough for a single water molecule to pass through. D.Two asparagines in the center of the pore prevent protons from passing through the channel.
Which of the following statements are true of mitochondrial proteins that are synthesized in the cytosol? Chaperone proteins help draw the proteins inside the mitochondrion. Proteins cross both the inner and outer mitochondrial membranes as they are imported. Protein transport into mitochondria is powered in part by ATP hydrolysis. Proteins usually have a signal sequence at their C-terminus. Proteins are unfolded as they are transported into the organelle. Proteins are transported across the mitochondrial membranes while being synthesized.
Chaperone proteins help draw the proteins inside the mitochondrion. Proteins cross both the inner and outer mitochondrial membranes as they are imported. Protein transport into mitochondria is powered in part by ATP hydrolysis. Proteins are unfolded as they are transported into the organelle.
Which best describes a pathway that a protein might follow from synthesis to secretion? Cytosol → ER → Golgi apparatus → transport vesicle → endosome → secretory vesicle → plasma membrane ER → Golgi apparatus → transport vesicle → endosome → secretory vesicle → plasma membrane ER → Golgi apparatus → secretory vesicle → plasma membrane Cytosol → ER → transport vesicle → Golgi apparatus → transport vesicle → plasma membrane Cytosol → ER → secretory vesicle → plasma membrane
Cytosol → ER → transport vesicle → Golgi apparatus → transport vesicle → plasma membrane
A sodium-potassium antiport maintains the extracellular concentration of sodium at levels that are about 20-30 times higher than inside the cells. What directly supplies the energy for maintaining this gradient? A. A proton gradient in the mitochondria drives the antiport. B. Sodium supplies the energy, as it is moving along its concentration gradient. C. Potassium supplies the energy, as it is moving along its concentration gradient. D. ATP hydrolysis drives the function of the pump.
D. ATP hydrolysis drives the function of the pump.
How do clathrin-coated vesicles select their cargo molecules? A. Specific cargo molecules have a high affinity for clathrin. B. Cargo is actively transported into preformed clathrin-coated vesicles. C. Cargo is selected randomly and is sorted later in the endosomes. D. Cargo receptors bind specifically to cargo proteins and to clathrin.
D. Cargo receptors bind specifically to cargo proteins and to clathrin.
For voltage-gated channels, a change in the membrane potential has what effect on the channel? A. It changes the width of the channel opening. B. It changes which ions can pass through the channel. C. It makes the channel more sensitive to the binding of neurotransmitters. D. It alters the probability that the channel will be found in its open conformation. E. It either opens the channel or closes it, depending on the voltage.
D. It alters the probability that the channel will be found in its open conformation.
When an individual ion channel is stimulated to open (for example, by the binding of a neurotransmitter), what is the typical activity of the ion channel? A. It opens partially and will open fully once neighboring channels begin to open. B. It opens and then very quickly closes, triggering the neurotransmitter to detach. C. It opens and stays open until the neurotransmitter detaches. D. It continues to flicker between open and closed states, but spends more time open while the neurotransmitter is bound. E. It opens to allow the neurotransmitter to enter the cell.
D. It continues to flicker between open and closed states, but spends more time open while the neurotransmitter is bound.
When voltage-gated Na+ channels in a nerve cell open, what happens to the axonal membrane? A. No change in the membrane potential occurs. B. It becomes electrically charged. C. The nerve cell becomes more negatively charged inside than outside. D. It depolarizes. E. The membrane potential rises to 0 mV and stays there.
D. It depolarizes.
When transmitter-gated ion channels in the membrane of a postsynaptic cell open in response to neurotransmitter binding, what happens? A. The channels remain open until an inhibitory neurotransmitter triggers their closure. B. The channels convert an electrical signal to a chemical signal. C. The channels always trigger an immediate and sustained action potential. D. The channels alter the ion permeability of the postsynaptic membrane, which in turn may depolarize the postsynaptic membrane.
D. The channels alter the ion permeability of the postsynaptic membrane, which in turn may depolarize the postsynaptic membrane.
You have attached green fluorescent protein (GFP) to the carboxy terminal end of a secreted yeast protein. You express this protein in normal yeast cells, secretory mutant A cells, and secretory mutant B cells (see image). Using fluorescent microscopy, you observe the expected results, with protein secretion in normal cells, ER accumulation in mutant A, and Golgi apparatus accumulation in mutant B. You also express the GFP-fusion protein in double-mutant yeast cells containing mutations in both the gene underlying mutant A and the gene underlying mutant B. What is the correct location and explanation for where the GFP-fusion protein will accumulate in these A and B double-mutant yeast cells? A. The protein will be secreted because the two different mutants will cancel each other out. B. The protein will accumulate in the Golgi apparatus because that is an earlier step in the secretory pathway. C. The protein will accumulate in the Golgi apparatus because that is a later step in the secretory pathway. D. The protein will accumulate in the ER because that is an earlier step in the secretory pathway.
D. The protein will accumulate in the ER because that is an earlier step in the secretory pathway.
What condition must exist for glucose to be transported into a cell using the glucose-Na+ symport? A. high Na+ concentration inside the cell B. high glucose concentration outside the cell C. high ATP concentration inside the cell for phosphorylation of the glucose-Na+ symport D. high Na+ concentration outside the cell
D. high Na+ concentration outside the cell
Which of the following organelles is NOT a part of the endomembrane system? A. lysosomes B. Golgi apparatus C. endoplasmic reticulum D. nucleus
D. nucleus
Which of the following pathways helps selectively concentrate substances to be ingested by their binding to proteins on the cell surface? A. pinocytosis B. phagocytosis C. exocytosis D. receptor-mediated endocytosis
D. receptor-mediated endocytosis
Which of the following statements is true? A. Inside the cell, there are no positively charged ions. B. Inside the cell, the quantity of positively charged ions is much greater than the quantity of negatively charged ions. C. Inside the cell, the quantity of positively charged ions is much less than the quantity of negatively charged ions. D. Inside the cell, there are no negatively charged ions. E. Inside the cell, the quantity of positively charged ions is almost equal to the quantity of negatively charged ions.
E. Inside the cell, the quantity of positively charged ions is almost equal to the quantity of negatively charged ions.
What is not true about a nerve impulse? A. It is another term for an action potential. B. It can travel long distances without weakening. C. It can travel at speeds of 100 meters per second. D. It is electrical excitation of the plasma membrane that is propagated rapidly along the membrane and sustained by automatic renewal along the way. E. It depends entirely on the action of ligand-gated ion channels.
E. It depends entirely on the action of ligand-gated ion channels.
Which of the following form tiny hydrophilic pores in the membrane through which solutes can pass by diffusion? A. transporters B. anions C. pumps D. liposomes E. channels
E. channels
What is the name of the specialized junction between a neuron and a target cell? A. dendrite B. synaptic vesicle C. nerve terminal D. axon E. synapse
E. synapse
Proteins destined for the Golgi apparatus, endosomes, lysosomes, and even the cell surface must pass through which organelle? ER mitochondrion peroxisome nucleus
ER
Determine whether the following statement is true or false: Water passes through the cell membrane only through specialized channels called aquaporins. T/F
False
Which organelle cannot receive proteins directly from the cytosol? nucleus mitochondrion peroxisome Golgi apparatus chloroplast
Golgi apparatus
Your friend is attempting to study the function of the Na+-K+ pump and has created spherical liposomes that contain only the Na+-K+ pump. She has inserted the pumps so that the extracellular side of the pump is also outside the liposome. She has added different ions and energy sources to the beaker with the liposomes, but no pumping of ions occurs. You explain that components must be in the proper location inside or outside the liposome for the pump to work. Help her by adding the proper components to the inside or outside of the liposome so that proper pumping occurs. Place unneeded components in the unneeded box. The figure shows a spherical liposome formed from phospholipids. Categories: Inside the Liposome Outside the Liposome Unneeded Items: ATP K+ GTP Cl- Na+
Inside the Liposome: ATP Na+ Outside the Liposome: K+ Unneeded: GTP Cl-
As a polypeptide is being translocated across the membrane of the endoplasmic reticulum, a stop-transfer sequence can halt the process. What eventually becomes of this stop-transfer sequence? It is cleaved from the protein. It forms an α-helical membrane-spanning segment of the protein. It is translocated into the lumen of the endoplasmic reticulum. It remains in the cytosol. It stops protein synthesis and causes the ribosome to be released back to the cytosol.
It forms an α-helical membrane-spanning segment of the protein.
The ER signal sequence on a growing polypeptide chain is recognized by a signal-recognition particle (SRP) in the cytosol. What does this interaction accomplish? It cleaves the ER signal sequence from the polypeptide chain. It guides the ribosome and its polypeptide to the ER. It returns the ribosome to the pool of free ribosomes in the cytosol. It speeds the synthesis of the polypeptide chain. It releases the polypeptide chain from the ribosome.
It guides the ribosome and its polypeptide to the ER.
What is true about the structure of the Golgi apparatus? It contains an inner membrane that is folded into cristae. It is a flattened set of membrane-enclosed sacs usually found near the nucleus. It is widely distributed throughout the cytosol. It is an extension of the endoplasmic reticulum. It is continuous with the outer nuclear membrane.
It is a flattened set of membrane-enclosed sacs usually found near the nucleus.
What is true of the inside of a cell? It is slightly more positive than the outside of a cell. It has the same charge as the outside of the cell. It is slightly more negative than the outside of a cell.
It is slightly more negative than the outside of a cell.
Which is true of the constitutive exocytosis pathway? It packages proteins that form aggregates in the conditions present in the trans Golgi. It packages proteins in secretory vesicles that accumulate near the plasma membrane. It packages proteins that carry a signal sequence that marks them for secretion. It operates continually in all eukaryotic cells. It replaces the regulated exocytosis pathway in cells specialized for secretion.
It operates continually in all eukaryotic cells.
If a signal sequence is removed from an ER protein, what happens to the altered protein? It remains in the cytosol. It is unable to exit the ER. It can enter any organelle other than the ER. It is immediately degraded. It is escorted to the ER by chaperone proteins.
It remains in the cytosol.
Which statement about receptor-mediated endocytosis of LDL particles is true? Mutations that impair the endocytosis of LDL receptors cause a drop in blood cholesterol levels. LDL receptors in the plasma membrane associate with clathrin-coated pits. LDL receptors are normally degraded in the lysosome along with LDL. LDL receptors are not taken up by receptor-mediated endocytosis unless they are carrying LDL. The high pH inside endosomes allows LDL to dissociate from its receptor.
LDL receptors in the plasma membrane associate with clathrin-coated pits.
Which statements are true regarding protein transport into peroxisomes? Like proteins transported into the nucleus, proteins must unfold before entering the peroxisome. Like mitochondria, peroxisomes contain translocators through which proteins enter the organelle. Like mitochondrial proteins, some peroxisomal proteins arrive via vesicles that bud from the ER. Like proteins destined for the ER, nucleus, or mitochondria, peroxisomal proteins bear a distinct signal sequence. Like proteins transported into mitochondria, proteins can enter the peroxisome in a folded conformation. Like prospective nuclear proteins, some peroxisomal proteins are recognized by receptor proteins in the cytosol.
Like mitochondria, peroxisomes contain translocators through which proteins enter the organelle. Like proteins destined for the ER, nucleus, or mitochondria, peroxisomal proteins bear a distinct signal sequence. Like prospective nuclear proteins, some peroxisomal proteins are recognized by receptor proteins in the cytosol.
Which of these statements is true? Only those proteins that are destined to remain inserted in the membrane are made on the rough ER; soluble proteins are made in the cytosol. The N-terminus of a protein translocated into the ER will always remain in the ER lumen. Membrane-bound ribosomes and free ribosomes are structurally and functionally identical; they differ only in the proteins they are making at a particular time. The signal sequence that directs a growing polypeptide chain to enter the ER membrane is always removed by a transmembrane signal peptidase. Attachment to a polyribosome prevents a growing polypeptide chain from being translocated into the ER.
Membrane-bound ribosomes and free ribosomes are structurally and functionally identical; they differ only in the proteins they are making at a particular time.
Lipid bilayers are highly impermeable to which molecule(s)? oxygen carbon dioxide water steroid hormones Na+ and Cl-
Na+ and Cl-
Which of the following statements is true? K+ and Na+ are present in the same concentration on both sides of the plasma membrane. K+ and Na+ are both maintained at high concentrations inside the cell compared to out. K+ and Na+ are both excluded from cells. Na+ is the most plentiful positively charged ion outside the cell, while K+ is the most plentiful inside. K+ is the most plentiful positively charged ion outside the cell, while Na+ is the most plentiful inside.
Na+ is the most plentiful positively charged ion outside the cell, while K+ is the most plentiful inside.
How does the nuclear pore restrict the passage of large molecules that do not bear the correct nuclear localization signal? The pores remain closed until they are stimulated by the binding of proteins with the proper localization signal. The cytosolic fibrils obstruct access to the pore and can only be parted by nuclear import receptors. Inbound proteins are captured by the nuclear basket and released by GTP hydrolysis. Nuclear pore proteins contain disordered segments that form a gel-like meshwork inside the pore. The hydrophobic interior of the pore repels proteins that lack the correct nuclear localization signal.
Nuclear pore proteins contain disordered segments that form a gel-like meshwork inside the pore.
Nuclear import is driven by the hydrolysis of GTP, which is triggered by an accessory protein called Ran-GAP (GTPase-activating protein). Which is true of this process? Nuclear import receptors have the ability to catalyze hydrolysis of GTP. Ran-GTP is present in high concentrations in the cytosol. Nuclear receptors carry Ran-GTP from the nucleus to the cytosol. Ran-GAP is present exclusively in the nucleus. Ran-GDP displaces proteins from nuclear import receptors inside the nucleus.
Nuclear receptors carry Ran-GTP from the nucleus to the cytosol.
What is true of protein glycosylation in the ER? Oligosaccharides are added by an enzyme that has its active site on the lumenal side of the ER membrane. Sugar residues are added one at a time by a series of enzymes attached to the ER membrane. Only proteins phosphorylated on an asparagine residue become glycosylated. Only proteins bearing a dolichol residue become glycosylated. A block of sugar residues is added to the N-terminal signal sequence, creating a common, N-linked oligosaccharide.
Oligosaccharides are added by an enzyme that has its active site on the lumenal side of the ER membrane.
Signaling at a synapse occurs in presynaptic and postsynaptic cells. Sort each of the following events into the proper location. Categories: Presynaptic Cell Postsynaptic Cell Items: Ligand-gated ion channels open in response to neurotransmitter. Voltage-gated Ca2+ channels open. Reuptake of the neurotransmitter occurs. Neurotransmitter binding begins a new action potential. Neurotransmitter is released into the synaptic cleft.
Presynaptic Cell: Neurotransmitter is released into the synaptic cleft. Voltage-gated Ca2+ channels open. Reuptake of the neurotransmitter occurs. Postsynaptic Cell: Neurotransmitter binding begins a new action potential. Ligand-gated ion channels open in response to neurotransmitter.
Which proteins play a central role in the fusion of a vesicle with a target membrane? SNAREs clathrin adaptin Rab proteins tethering proteins
SNAREs
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. The A chain binds to clathrin. The B chain interacts with SNAREs. The protein enters through pore complexes in the plasma membrane. The A chain stimulates autophagy.
The protein is internalized by endocytosis.
Investigators have engineered a gene that encodes a protein bearing an ER signal sequence followed by a nuclear localization signal. What would be the likely fate of that protein? Because of its conflicting signals, the protein will be sent to a lysosome for destruction. The protein will be recognized by an SRP and enter the ER. Because of its conflicting signals, the protein will remain in the cytosol. Because of its conflicting signals, the protein will be degraded in the cytosol. The protein will be recognized by a nuclear import receptor and escorted into the nucleus.
The protein will be recognized by an SRP and enter the ER.
Which is true of water-soluble proteins transferred from the cytosol to the ER? They must fold properly to be able to enter the ER. They do not require an ER signal sequence. They are often destined for secretion. In most cases, their signal sequence remains attached to the C-terminus. In most cases, their signal sequence remains attached to the N-terminus.
They are often destined for secretion.
What enables proteins destined for nuclear import to pass through the nuclear pore? Their nuclear localization signal interacts with the cytosolic fibrils that extend from the pore. Their nuclear localization signal interacts with the unstructured meshwork of proteins lining the pore. They are unfolded to allow them to snake through the meshlike network of proteins lining the nuclear pore. They are recognized by receptors that interact with repeated amino acid sequences in proteins lining the nuclear pore. They promote the hydrolysis of GTP, which provides the energy needed for their transport.
They are recognized by receptors that interact with repeated amino acid sequences in proteins lining the nuclear pore.
What happens to the final products of the digestion of macromolecules? They are removed from the lysosome by transport vesicles that carry them to where they are needed. They are secreted from the cell when lysosomes fuse with the plasma membrane. They are ultimately destroyed by lysosomal enzymes. They are expelled from the lysosome by H+ pumps in the lysosomal membrane. They are transferred to the cytosol through transporters in the lysosomal membrane.
They are transferred to the cytosol through transporters in the lysosomal membrane.
How are proteins destined to function in the ER retained there? They retain their N-terminal ER signal sequence. They contain a C-terminal ER retention signal. They bind to chaperones within the ER. They are embedded in the ER membrane by a transmembrane α helix. They are anchored to dolichol in the ER membrane.
They contain a C-terminal ER retention signal.
Communication between neurons involves an interconversion of electrical and chemical signals. T/F
True
In muscle cells, which organelle sequesters Ca2+ from the cytosol? endosome rough ER lysosome smooth ER mitochondrion
smooth ER
Following an action potential, a nerve cell goes through a brief refractory period during which it cannot be stimulated. What is true during this refractory period? The membrane potential remains unchanged. Voltage-gated Na+ channels in the nerve cell membrane are open. Voltage-gated K+ channels in the nerve cell membrane are inactivated. Voltage-gated Na+ channels in the nerve cell membrane are inactivated. Voltage-gated Ca2+ channels are open.
Voltage-gated Na+ channels in the nerve cell membrane are inactivated.
The movement of an ion against its concentration gradient is called what? facilitated diffusion osmosis passive transport active transport
active transport
Which of these strategies do prokaryotic cells use to isolate and organize their chemical reactions? confining the proteins required for different metabolic processes within the plasma membrane confining proteins required for different metabolic processes within different membrane-enclosed compartments aggregating proteins into multicomponent complexes that form biochemical subcompartments with distinct functions None; these strategies are used only by eukaryotic cells. None; prokaryotes do not regulate their metabolic processes.
aggregating proteins into multicomponent complexes that form biochemical subcompartments with distinct functions
Inhibitory neurotransmitters such as glycine and GABA make a postsynaptic cell harder to depolarize by allowing what? an influx of K+ an influx of Cl- an influx of Na+ the escape of Na+
an influx of Cl-
Vesicle budding is driven by which of the following? assembly of a protein coat capture of Rabs by tethering proteins hydrolysis of ATP by dynamins binding of a cargo molecule interactions of v- and t-SNAREs
assembly of a protein coat
Which type of protein binds to improperly folded or improperly assembled proteins in the ER, holding them there until proper folding occurs? oligosaccharyl transferase antibodies chaperones tethering proteins ER retention signals
chaperones
Proteins have to be unfolded to cross the membranes of which of these organelles? chloroplasts nucleus endoplasmic reticulum mitochondria
chloroplasts endoplasmic reticulum mitochondria
What determines the direction that glucose is transported across the membrane, through a glucose transporter? a molecule's charge concentration gradient membrane potential a molecule's size
concentration gradient
Phagocytosis is a process by which cells do which of the following? consume large particles, such as microbes and cell debris ingest extracellular fluid and macromolecules secrete hormones and neurotransmitters engage in receptor-mediated endocytosis digest their own worn-out organelles
consume large particles, such as microbes and cell debris
Most mitochondrial and chloroplast proteins are made within which part of the cell? mitochondrion or chloroplast itself cytosol peroxisome Golgi apparatus endoplasmic reticulum
cytosol
Proteins that lack a sorting signal remain as permanent residents of which part of a eukaryotic cell? cytosol nucleus Golgi apparatus proteasome ER
cytosol
The movement of materials from the plasma membrane, through endosomes, and then to lysosomes describes which type of pathway? endolytic pathway endosomal pathway endocytic pathway exocytic pathway secretory pathway
endocytic pathway
Which organelle is the major site of new membrane synthesis in a cell? nucleus Golgi apparatus endoplasmic reticulum peroxisome mitochondrion
endoplasmic reticulum
Which organelle sorts ingested molecules and recycles some of them back to the plasma membrane? lysosome Golgi apparatus endosome peroxisome endoplasmic reticulum
endosome
Which cellular compartment acts as the main sorting station for extracellular cargo molecules taken up by endocytosis? Golgi apparatus transport vesicles endosomes clathrin-coated vesicles lysosomes
endosomes
Eukaryotic cells continually ingest bits of their plasma membrane, along with small amounts of extracellular fluid. The lost pieces of membrane are replaced by what process? endocytosis pinocytosis exocytosis phagocytosis
exocytosis
Glucose enters the cell by which process? osmosis facilitated diffusion active transport simple diffusion
facilitated diffusion
Trypanosomes are single-celled parasites that cause sleeping sickness when they infect humans. Trypanosomes taken from infected humans are known to store the enzymes needed to carry out some of the reactions of glycolysis in an organelle that resembles the peroxisome. In contrast, trypanosomes taken from tsetse flies—the intermediate host—carry out glycolysis entirely in the cytosol. Investigators at a pharmaceutical company decide to follow up on this observation to design a potential new therapeutic. They determine that in trypanosomes from tsetse flies, one of the glycolytic enzymes, phosphoglycerate kinase (PGK), is present entirely in the cytosol, whereas in parasites taken from humans, 90% of the PGK activity is in a peroxisome-like compartment and only 10% is in the cytosol. When the investigators clone the PGK genes, they discover that the parasites have three forms, each of which differs slightly from the others. They design probes that hybridize specifically to the mRNAs from each gene and then use these probes to determine which genes are expressed by trypanosomes from humans (H) and which are expressed by trypanosomes from tsetse flies (F). Shown here is a gel in which mRNAs purified from the two different trypanosomes have been separated by size and exposed to probes that recognize the three different forms of the PGK gene (genes 1, 2, and 3). Based on these results, which gene most likely encodes the peroxisomal form of PGK? gene 3 gene 1 both genes 1 and 2 gene 2 both genes 1 and 3
gene 3
Lysosomes contain ____________ enzymes that can break down diverse macromolecules, cell parts, and microorganisms. biosynthetic isomerase hydrolytic kinase
hydrolytic
Proteins encoded by nuclear genes and destined for the mitochondrial matrix are able to diffuse into the mitochondrial intermembrane space first. transported across the membrane as a folded protein. in possession of a signal sequence for targeting to the mitochondria. synthesized on ribosomes on the rough ER.
in possession of a signal sequence for targeting to the mitochondria.
In passive transport, the net movement of a charged solute across the membrane is determined by which of the following? its electrochemical gradient the membrane potential its osmotic gradient alone its concentration gradient
its electrochemical gradient
Which of these actions occur(s) commonly at a nuclear pore complex? Small water-soluble molecules are selectively transported into the nucleus. mRNA molecules are exported to the cytosol. Nuclear import receptors enter from the cytosol. Protein complexes diffuse into the nucleus. Nuclear import receptors are exported to the cytosol. Proteins with a nuclear localization signal enter at the same time that proteins with a nuclear export signal exit.
mRNA molecules are exported to the cytosol. Nuclear import receptors enter from the cytosol. Nuclear import receptors are exported to the cytosol. Proteins with a nuclear localization signal enter at the same time that proteins with a nuclear export signal exit.
Which proteins bind to nuclear localization signals on newly synthesized proteins? signal-recognition particles (SRPs) cytosolic fibrils nuclear import receptors nuclear pore proteins nuclear export receptors
nuclear import receptors
A transmembrane protein has the structure shown. If an ER signal sequence were added to its N-terminus, which structure would the engineered protein adopt?
option where there is 1 curve at the top, 1 and 2 are pointing down and end in the curly tails of N and C, respectively.
The movement of an ion down its concentration gradient is called what? active transport osmosis pumping passive transport
passive transport
Which organelle contains enzymes used in a variety of oxidative reactions that break down lipids and destroy toxic molecules? peroxisome mitochondrion lysosome endoplasmic reticulum endosome
peroxisome
In the unfolded protein response, the accumulation of misfolded proteins in the ER serves as a signal for the cell to do which of the following? export the misfolded proteins to the cytosol glycosylate the misfolded protein send the misfolded proteins to the Golgi apparatus for modification and folding produce more ER destroy the misfolded proteins
produce more ER
Viruses such as influenza and HIV enter cells via which of these processes? apoptosis receptor-mediated endocytosis autophagy pinocytosis
receptor-mediated endocytosis
In a typical human secretory cell, which of the following membranes has the largest surface area? nuclear inner membrane plasma membrane rough ER lysosome smooth ER
rough ER
Endocrine cells that synthesize lipid hormones, such as steroids, contain extensive amounts of which of the following? cytosol Golgi apparatus rough ER smooth ER nucleus
smooth ER
Which membrane-enclosed organelles most likely evolved in a similar manner? the nucleus and the ER chloroplasts and peroxisomes mitochondria and the ER mitochondria and the nucleus mitochondria and the Golgi apparatus
the nucleus and the ER
In a classic experiment designed to study nuclear transport, investigators added a dye molecule to the subunits of a protein called nucleoplasmin, which is involved in chromatin assembly. They then injected the intact protein or combinations of its subunits into the cytosol of a frog oocyte or into its nucleus. The results of the experiment are shown in the diagram, where red indicates the location of the labeled protein. Based on these results, which part of the nucleoplasmin protein bears a nuclear localization signal? the head only neither the head nor the tail both the head and the tail the tail only No conclusion about the nuclear localization signal can be drawn from the data.
the tail only
The depolarization of the nerve-terminal plasma membrane triggers the secretion of neurotransmitters by opening which of the following? voltage-gated Ca2+ channels in the sarcoplasmic reticulum voltage-gated Na+ channels in the plasma membrane voltage-gated Ca2+ channels in the plasma membrane transmitter-gated Ca2+ channels in the plasma membrane voltage-gated K+ channels in the plasma membrane
voltage-gated Ca2+ channels in the plasma membrane