EXAM 3 PRACTICE Qs
Dynamic instability in microtubules stems from the intrinsic capacity of tubulin molecules to hydrolyze: A. peptide bonds. B. tubulin dimers. C. GTP. D. ATP.
C. GTP
Which of the following organelles is not surrounded by a double membrane? A. Mitochondrion B. Chloroplast C. Golgi apparatus D. Nucleus
C. Golgi apparatus
Which mechanism is used for degrading obsolete parts of a cell, such as a defective mitochondrion? A. Phagocytosis B. The unfolded protein response C. Apoptosis D. Autophagy
D. Autophagy
Synaptic plasticity is largely dependent on the presence of which ion in the postsynaptic cell? A. H+ B. Na+ C. K+ D. Ca2+
D. Ca2+
The glucose-Na+ symport in epithelial cells uses the electrochemical gradient of Na+ to draw glucose into the cell. A. True B. False
A. True
The nuclear lamina disassembles and re-forms at each cell division. A. True B. False
A. True
The proteins targeted by either the /alpha subunit or the /alpha//beta complex of a G-protein are either enzymes or ion channels in the plasma membrane. A. True B. False
A. True
Vesicle budding is driven by the assembly of a protein coat. A. True B. False
A. True
When glucose moves across a phospholipid bilayer by passive transport, which factor determines the direction of its transport? A. (A) The concentrations of glucose on either side of the membrane B. (B) The charge difference across the membrane C. (C) The amount of energy available to fuel the transport process D. All of the above E. A and B, but not C
A. (A) The concentrations of glucose on either side of the membrane
In a lipid bilayer, which behaves like a two-dimensional fluid, lipids rapidly diffuse: A. (A) within the plane of one monolayer in the bilayer. B. (B) back and forth from one monolayer to the other in the bilayer. C. Both A and B D. Neither A nor B
A. (A) within the plane of one monolayer in the bilayer.
Which G protein component or components have GTPase activity? A. /alpha subunit B. /beta subunit C. /gamma subunit D. /alpha//beta complex
A. /alpha subunit
Which of the following statements describes a 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 measure of 0 millivolts (mV) across the membrane C. A value that is chiefly a reflection of the Na+ concentration gradient across the plasma membrane
A. A state in which the flow of positive and negative ions across the plasma membrane is precisely balanced
Kinesin and dynein motor proteins each use the energy of ____ to power their movements _______ along microtubules. A. ATP hydrolysis, in a single direction B. ATP hydrolysis, in both directions C. GTP hydrolysis, in a single direction D. GTP hydrolysis, in both directions
A. ATP hydrolysis, in a single direction
Which organelle sorts ingested molecules and recycles some of them back to the plasma membrane? A. An endosome B. The Golgi apparatus C. A lysosome D. The endoplasmic reticulum E. A peroxisome
A. An endosome
The interiors of the ER, Golgi apparatus, endosomes, and lysosomes communicate with each other in which of the following ways? A. By small vesicles that bud off of one organelle and fuse with another B. By open pores that allow ions to exit and enter the organelles C. They do not communicate with one another. D. By excreting hormones and other small signaling molecules
A. By small vesicles that bud off of one organelle and fuse with another
How do proteins travel from one cisterna to the next in the Golgi apparatus? A. By transport vesicles that bud off from one cisterna and fuse with the next cisterna B. By physical connections between two cisternae C. Through pores in the membranes of cisternae
A. By transport vesicles that bud off from one cisterna and fuse with the next cisterna
Contractions in smooth muscle cells depend on which one of the following activation steps? A. Ca2+-activated phosphorylation of myosin-II B. Ca2+ binding to troponin C. GTP binding to myosin-II D. Actin polymerization
A. Ca2+-activated phosphorylation of myosin-II
How does cholesterol in animal cell membranes affect the fluidity of the bilayer? A. Cholesterol tends to stiffen the bilayer. B. Cholesterol tends to make the bilayer more fluid. C. Cholesterol has little effect on membrane fluidity.
A. Cholesterol tends to stiffen the bilayer.
As a cell grows, which microtubule-associated protein pulls the Golgi apparatus inward toward the nucleus? A. Dynein B. Cohesin C. Actin D. Kinesin
A. Dynein
When the hormone insulin is released into the bloodstream, what form of cell-to-cell signaling is being used? A. Endocrine B. Paracrine C. Neuronal D. Contact-dependent
A. Endocrine
The end of a growing microtubuleis rich in which type of tubulin molecule? A. GTP-associated tubulin molecules B. GDP-associated tubulin molecules
A. GTP-associated tubulin molecules
Most mitochondrial and chloroplast proteins are made in which compartment of the cell? A. In the cytosol B. In the endoplasmic reticulum C. Within the mitochondrion or chloroplast
A. In the cytosol
Which is the toughest and most durable of the three types of cytoskeletal filaments? A. Intermediate filaments B. Microtubules C. Actin filaments
A. Intermediate filaments
Which of the following statements is true? A. Ion-channel-coupled receptors can rapidly alter the membrane potential in response to neurotransmitter binding. B. G-protein-coupled receptors are GTP-binding proteins. C. Enzyme-coupled receptors always have an intrinsic catalytic domain on the cytosolic side of the plasma membrane.
A. Ion-channel-coupled receptors can rapidly alter the membrane potential in response to neurotransmitter binding.
In the process of translocating a polypeptide across the membrane of the endoplasmic reticulum, a stop transfer sequence halts the process. What eventually becomes of the stop transfer sequence? A. It forms an /alpha-helical membrane-spanning segment of the protein. B. It is cleaved from the protein. C. It is translocated into the lumen of the endoplasmic reticulum.
A. It forms an /alpha-helical membrane-spanning segment of the protein.
Which of the following accurately describes the role of the Na+ pump? A. It maintains a high Na+ concentration outside the cell. B. It maintains a high K+ concentration outside the cell. C. It maintains a low Na+ concentration outside the cell. D. It equilibrates the concentrations of Na+ and K+ across the plasma membrane.
A. It maintains a high Na+ concentration outside the cell.
Which of the following statements is true? A. Na+ is the most plentiful positively charged ion outside the cell, while K+ is the most plentiful inside. B. K+ is the most plentiful positively charged ion outside the cell, while Na+ is the most plentiful inside. C. K+ and Na+ are carefully balance on each side of the cell.
A. Na+ is the most plentiful positively charged ion outside the cell, while K+ is the most plentiful inside.
When a neuron is stimulated by a signal, the response is at first spread locally along the membrane by what means? A. Passive spread B. Active transport C. Action potential
A. Passive spread
All other factors (e.g., concentration, solute size) being equal, which type of solute does a cell tend to pull inside? A. Positively charged solutes B. Negatively charged solutes C. Uncharged solutes
A. Positively charged solutes
Which of the following statements is false? A. Serine/threonine protein kinases phosphorylate extracellular proteins on serines and/or threonines. B. Tyrosine protein kinases phosphorylate intracellular proteins on tyrosines. C. Serine/threonine protein kinases phosphorylate intracellular proteins on serines and/or threonines.
A. Serine/threonine protein kinases phosphorylate extracellular proteins on serines and/or threonines.
What is the name of the specialized junction between a neuron and a target cell? A. Synapse B. Dendrite C. Nerve terminal
A. Synapse
Which parts of the phospholipid face the outside of the membrane? A. The head B. The tail C. The belly
A. The head
Proteins have to unfold during their transport across the membranes of all but one of the following organelles. Which one? A. The nucleus B. Mitochondria C. Chloroplasts D. The endoplasmic reticulum
A. The nucleus
During an action potential, which of the following actions does not help return the membrane to its resting potential? A. The opening of voltage-gated Na+ channels B. The opening of voltage-gated K+ channels C. The inactivation of voltage-gated Na+ channels
A. The opening of voltage-gated Na+ channels
Proteins entering the cisGolgi network can do which of the following? A. They can either move onward through the Golgi stack or be returned to the ER. B. They can either move backward through the Golgi stack or be sent to the plasma membrane. C. They are sorted according to whether they are destined for lysosomes or for the cell surface.
A. They can either move onward through the Golgi stack or be returned to the ER.
What distinguishes proteins destined for regulated secretion? A. They have special surface properties that cause them to form aggregates that are packaged into secretory vesicles. B. They have a series of amino acids that act as a tag that marks them for packaging into secretory vesicles. C. They are cleaved from membrane domains in the Golgi apparatus prior to being packed into secretory vesicles.
A. They have special surface properties that cause them to form aggregates that are packaged into secretory vesicles.
Which type of membrane transport protein can perform either passive or active transport? A. Transporters B. Channels
A. Transporters
Both GPCRs and RTKs can activate the inositol phospholipid signaling pathway because they both can activate phospholipase C enzymes (although the enzymes are not exactly the same). A. True B. False
A. True
During muscle contraction, the myosin and actin filaments do not change in length. A. True B. False
A. True
In the Notch signaling pathway, the tail of the cell surface receptor travels to the nucleus where it regulates the transcription of specific genes. A. True B. False
A. True
Signaling via a GPCR ceases when the /alpha subunit of an activated G protein hydrolyzes its bound GTP to GDP. A. True B. False
A. True
Some dissolved gases cross the plasma membrane and activate intracellular enzymes directly. A. True B. False
A. True
The communication between neurons involves the conversion between electrical and chemical signals. A. True B. False
A. True
The constitutive exocytosis pathway of the Golgi apparatus operates continually in all eucaryotic cells. A. True B. False
A. True
The cyclic AMP pathway can both activate enzymes and turn on genes. A. True B. False
A. True
Which type of ion channel plays the major role in propagating electrical signals in nerve cells? A. Voltage-gated B. Ligand-gated C. Stress-gated
A. Voltage-gated
Cell crawling depends on: A. actin polymerization. B. microtubule assembly. C. hydrolysis of ADP by motor proteins. D. intermediate filaments.
A. actin polymerization.
Cholera and whooping cough both are caused by bacteria that: A. alter the function of G proteins. B. alter the function of ion-gated channels. C. disable a G protein. D. take up residence inside white blood cells.
A. alter the function of G proteins.
When transmitter-gated ion channels in the membrane of a post-synaptic cell open in response to neurotransmitter binding, they: A. alter the ion permeability of the postsynaptic membrane, which in turn may depolarize the postsynaptic membrane. B. trigger an immediate and sustained action potential. C. remain open until an inhibitory neurotransmitter triggers their closure.
A. alter the ion permeability of the postsynaptic membrane, which in turn may depolarize the postsynaptic membrane.
GTP binding proteins, which act as molecular switches inside cells,: A. are active when GTP is bound. B. are active when GDP is bound. C. turn themselves on by cleaving GTP to form GDP. D. are active only in their trimeric forms.
A. are active when GTP is bound.
When a muscle is stimulated to contract: A. calcium binds to troponin which moves the tropomyosin that otherwise blocks the interaction of actin and myosin. B. calcium binds to tropomyosin which moves the troponin that otherwise blocks the interaction of actin and myosin. C. calcium binds to actin allowing it to associate with myosin. D. calcium binds to myosin allowing it to associate with actin.
A. calcium binds to troponin which moves the tropomyosin that otherwise blocks the interaction of actin and myosin.
The tails of phospholipids are: A. hydrophobic B. hydrophilic C. amphipathic
A. hydrophobic
A key group of proteins that regulate the actin cytoskeleton is: A. the Rho protein family. B. the Rab protein family. C. the Ran protein family. D. the Rheb protein family.
A. the Rho protein family.
If a signal sequence is removed from an ER protein: A. the protein remains in the cytosol. B. the protein will enter an organelle other than the ER. C. the protein will be immediately degraded. D. the protein will be exported from the cell.
A. the protein remains in the cytosol.
Given enough time, virtually any molecule will diffuse across a lipid bilayer. A. True B. False
A. true
In the /alpha helices of transmembrane proteins, the hydrophobic side chains are facing: A. the inside of the membrane-spanning helix. B. the outside of the membrane-spanning helix.
B. the outside of the membrane-spanning helix.
Which subunit of a G protein is not tethered to the plasma membrane by a short lipid tail? A. /alpha subunit B. /beta subunit C. /gamma subunit
B. /beta subunit
In one second, a lipid in an artificial bilayer may diffuse as far as what distance? A. 2 nanometers (the width of a DNA double helix) B. 2 microns (the length of a large bacterial cell) C. 500 microns (the length of a typical amoeba)
B. 2 microns (the length of a large bacterial cell)
How much of the mass of the plasma membranes is constituted by proteins? A. 25% B. 50% C. 75%
B. 50%
( start of chapter 12 ) Which of the following membrane transport proteins forms tiny hydrophilic pores in the membrane through which solutes can pass by diffusion? A. A transporter B. A channel C. A pump
B. A channel
Which of the following is true? A. A special class of ribosomes embedded in the ER translates the proteins destined for that organelle. B. A common pool of ribosomes is used to synthesize both the proteins that stay in the cytosol and those that are destined for the ER. C. All ribosomes are attached to the ER when they are synthesizing a protein.
B. A common pool of ribosomes is used to synthesize both the proteins that stay in the cytosol and those that are destined for the ER.
An electrochemical gradient has a chemical component and voltage component. Which of the following will have the largest electrochemical gradient? A. A positively charged ion present in high concentrations inside the cell B. A positively charged ion present in high concentrations outside the cell C. A negatively charged ion present in high concentrations inside the cell D. A negatively charged ion present in high concentrations outside the cell
B. A positively charged ion present in high concentrations outside the cell
In general, which of the following will diffuse across a lipid bilayer most rapidly? A. A small hydrophilic molecule B. A small hydrophobic molecule C. A large hydrophilic molecule D. A large hydrophobic molecule
B. A small hydrophobic molecule
Inside a muscle fiber, what triggers sarcomeres to contract? A. A sudden rise in intracellular Na+ B. A sudden rise in intracellular Ca2+ C. An increased availability of ATP D. Polarization of the muscle fiber's membrane
B. A sudden rise in intracellular Ca2+
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? A. Na+ B. Ca2+ C. K+ D. Cl-
B. Ca2+
The concentration of free Ca2+ in the cytosol of an unstimulated cell is kept low compared with its concentration in both the extracellular fluid and the endoplasmic reticulum. Which of the following does not help maintain this difference? A. Membrane-bound Ca2+ pumps in the plasma membrane B. Ca2+-destroying enzymes in the cytosol C. Membrane-bound Ca2+ pumps in the ER membrane D. Ca2+-binding proteins in the cytosol
B. Ca2+-destroying enzymes in the cytosol
Which of the following statements is true about the concentration of calcium ions in cells? A. 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. C. 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.
What is the difference between transporters and channels? A. 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. B. 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. C. 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.
B. 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.
What protein can assemble into a basket-like network that gives budding vesicles their shape? A. Dynamin B. Clathrin C. Actin D. Myosin
B. Clathrin
Which is not a mechanism for restricting the movement of proteins in the membrane? A. Using barriers such as tight junctions B. Coating proteins with carbohydrates C. Tethering proteins to the cell cortex D. Tethering proteins to the extracellular matrix E. Tethering proteins to the surface of another cell
B. Coating proteins with carbohydrates
Which of the following signaling molecules don't seem to be used by plants in cell-to-cell communication? A. GPCRs B. Cyclic AMP C. Ca2+ D. Enzyme-coupled receptors
B. Cyclic AMP
( start of chapter 11 ) Which is not found in a cell membrane? A. lipid B. DNA C. protein D. cholesterol
B. DNA
When activated phospholipase C chops the head off an inositol phospholipid, it produces two small signaling molecules that relay the signal onward. Which of these stays in the plasma membrane? A. Inositol 1,4,5-trisphosphate (IP3) B. Diacylglycerol (DAG)
B. Diacylglycerol (DAG)
Double bonds in hydrocarbon tails have what effect on the rigidity of fats and phospholipid bilayers? A. Double bonds increase the ability of hydrocarbon tails to pack together into a rigid mass. B. Double bonds decrease the ability of hydrocarbon tails to pack together into a rigid mass. C. Double bonds have little effect on the rigidity of fats and phospholipid bilayers.
B. Double bonds decrease the ability of hydrocarbon tails to pack together into a rigid mass.
In passive transport, a charged solute moves spontaneously in which way? A. Down its concentration gradient B. Down its electrochemical gradient C. Down its osmotic gradient
B. Down its electrochemical gradient
The movement of materials from the plasma membrane, through endosomes, and then to lysosomes describes which type of pathway? A. Secretory pathway B. Endocytic pathway C. Exocytic pathway
B. Endocytic pathway
On what side of the membrane are the carbohydrate chains of glycoproteins, proteoglycans, and glycolipids located? A. Cytosolic side B. External (noncytosolic) side
B. External (noncytosolic) side
.An ion channel undergoes conformational changes with each ion it passes. A. True B. False
B. False
A given steroid hormone usually regulates the same sets of genes in different types of target cells. A. True B. False
B. False
An electrical signal crosses the synaptic cleft between the presynaptic and postsynaptic cells. A. True B. False
B. False
Each type of extracellular signal molecule induces a similar response in different target cells. A. True B. False
B. False
Intracellular signaling molecules can act on either intracellular receptors or cell-surface receptors. A. True B. False
B. False
Movement of materials in polarized cells by free diffusion is faster and more efficient than that guided by microtubules. A. True B. False
B. False
Optogenetics uses transmitter-gated channels that have been introduced by genetic engineering techniques to control neurons. A. True B. False
B. False
Parallel intracellular signaling pathways can interact, in part, because the protein kinases in one pathway can phosphorylate and thereby regulate proteins in other pathways. A. True B. False
B. False
Signaling cascades always operate at the same speeds irrespective of external stimuli. A. True B. False
B. False
Water passes through the cell membrane only through specialized channels called aquaporins. A. True B. False
B. False
What type of enzyme moves phospholipids from one monolayer to the other in a biological membrane? A. Phospholipase B. Flippase C. No enzyme-this action happens spontaneously and relatively quickly
B. Flippase
Which of the following is NOT a function of membrane proteins? A. Transport molecules across the membrane B. Generate the energy required for lipids to diffuse through the membrane C. Transmit extracellular signals to the cell interior D. Serve as anchors to attach the cell to the extracellular matrix
B. Generate the energy required for lipids to diffuse through the membrane
In fungi, plants, and bacteria, which pump helps to drive the import of solutes? A. ATP pumps B. H+ pumps C. Ca2+ pumps D. K+ pumps
B. H+ pumps
Porin proteins-which form large, water-filled pores in mitochondrial and bacterial membranes-fold into /beta barrel structures. The amino acids that face the outside of the barrel have what kind of side chains? A. Hydrophilic B. Hydrophobic
B. Hydrophobic
Intermediate filaments are found in what structure? A. The mitotic spindle B. Centrosomes C. Desmosomes D. Cilia
C. Desmosomes
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 alters the probability that the channel will be found in its open conformation. C. It either opens the channel or closes it, depending on the voltage.
B. It alters the probability that the channel will be found in its open conformation.
When Na+ channels are opened in an animal cell, what happens to the membrane potential? A. It stays the same. B. It becomes less negative. C. It becomes more negative.
B. It becomes less negative.
How does IP3 function in the inositol phospholipid pathway? A. It punches holes into the membrane surrounding the endoplasmic reticulum (ER), releasing Ca2+ from the ER into the cytosol. B. It binds to and opens Ca2+ channels that are embedded in the ER membrane, releasing Ca2+ into the cytosol. C. It directly activates protein kinase C. D. It activates phospholipase C.
B. It binds to and opens Ca2+ channels that are embedded in the ER membrane, releasing Ca2+ into the cytosol.
.When a neuron opens voltage-gated Na+ channels, what happens to the membrane? A. It polarizes B. It depolarizes C. No change in the membrane potential occurs
B. It depolarizes
Which of the following describes the structure of an actin filament? A. It is a hollow cylinder made up of actin molecules. B. It is a twisted chain of actin molecules. C. It is a structure with a long tail and two globular heads.
B. It is a twisted chain of actin molecules.
In most animal cells, which ion can move through "leak" channels in the plasma membrane and, in so doing, establishes the resting membrane potential? A. Cl- B. K+ C. Na+ D. Ca2+
B. K+
The Na+-K+ pump in the plasma membrane of animal cells uses the energy from ATP hydrolysis to pump sodium and potassium ions against their electrochemical gradients. In which direction are the ions pumped across the membrane? A. Na+ out and K+ in B. K+ in and Na+ out C. Na+ and K+ both out D. Na+ and K+ both in
B. K+ in and Na+ out
Which of the following cytoskeletal structures grows out from a centrosome toward the cell periphery? A. Intermediate filaments B. Microtubules C. Actin filaments
B. Microtubules
Which of the following cytoskeletal structures makes up the mitotic spindle? A. Intermediate filaments B. Microtubules C. Actin filaments
B. Microtubules
Which of the following cytoskeletal structures provides tracks for guiding intracellular transport? A. Intermediate filaments B. Microtubules C. Actin filaments
B. Microtubules
Which of the following has a larger electrochemical gradient across a cell's plasma membrane? A. K+ B. Na+
B. Na+
Which of the following would be deterred from entering an ion channel with negatively charged lining? A. Positively charged ions B. Negatively charged ions
B. Negatively charged ions
Which proteins bind to nuclear localization signals on newly synthesized proteins? A. Nuclear pore proteins B. Nuclear import receptors C. Signal-recognition particles D. Nuclear fibrils
B. Nuclear import receptors
Many of the extracellular signal molecules that regulate inflammation are released locally at the site of infection. What form of cell-to-cell signaling is being used? A. Endocrine B. Paracrine C. Neuronal D. Contact-dependent
B. Paracrine
Which of the following is not a small intracellular signaling molecule (second messenger)? A. Cyclic AMP B. Phospholipase C C. Inositol triphosphate D. Diacylglycerol
B. Phospholipase C
Which statement about phospholipids and detergents is NOT true? A. Phospholipids have two hydrocarbon tails, whereas detergents have just one. B. Phospholipids are amphipathic, whereas detergents are hydrophobic. C. Phospholipids form bilayers, whereas detergents tend to form micelles.
B. Phospholipids are amphipathic, whereas detergents are hydrophobic
Bacteriorhodopsin is a membrane transport protein that uses sunlight to do what? A. Hydrolyze ATP molecules B. Pump H+ out of the cell and generate a H+ gradient across the plasma membrane C. Pump photons into the cell and generate a deep purple color D. Convert CO2 into sugar during photosynthesis
B. Pump H+ out of the cell and generate a H+ gradient across the plasma membrane
Which term describes a coupled transporter that moves both solutes in the same direction across a membrane? A. Antiport B. Symport C. Uniport
B. Symport
Phospholipids with which of the following hydrocarbon tails will produce the most fluid bilayer? A. Tails with 18 carbon atoms, fully saturated B. Tails with 18 carbon atoms and two double bonds C. Tails with 20 carbon atoms, fully saturated D. Tails with 20 carbon atoms and two double bonds
B. Tails with 18 carbon atoms and two double bonds
Proteins that lack a sorting signal remain as permanent residents of which part of a eucaryotic cell? A. The nucleus B. The cytosol C. The endoplasmic reticulum D. The Golgi apparatus E. A lysosome
B. The cytosol
( start of chapter 15 ) The outer membrane of the nucleus is continuous with the membrane of which other organelle? A. A mitochondrion B. The endoplasmic reticulum C. The Golgi apparatus D. A peroxisome
B. The endoplasmic reticulum
Which organelle is the major site of new membrane synthesis in a cell? A. A mitochondrion B. The endoplasmic reticulum C. The Golgi apparatus D. The nucleus
B. The endoplasmic reticulum
Which cellular compartment acts as the main sorting station for extracellular cargo molecules taken up by endocytosis? A. Transport vesicles B. The Golgi apparatus C. Endosomes D. Lysosomes
C. Endosomes
Why do lipids form bilayers in water? A. The hydrophobic head is attracted to water while the hydrophilic tail shuns water. B. The hydrophilic head is attracted to water while the hydrophobic tail shuns water. C. The hydrophobic tail is attracted to water while the hydrophilic head shuns water. D. The hydrophobic head shuns water and the hydrophilic tail attracts water.
B. The hydrophilic head is attracted to water while the hydrophobic tail shuns water.
If GTP hydrolysis occurs on a tubulin molecule at the plus end of a microtubule protofilament before another tubulin molecule is added, what typically happens to the microtubule? A. The microtubule polymerizes. B. The microtubule depolymerizes. C. The microtubule remains the same size.
B. The microtubule depolymerizes.
Which end of a microtubule is embedded in the centrosome? A. The plus end B. The minus end
B. The minus end
In eukaryotic cells, new phospholipids are manufactured byenzymes bound to which part of the endoplasmic reticulum membrane? A. The monolayer that faces the lumen of the endoplasmic reticulum B. The monolayer that faces the cytosol C. Both monolayers
B. The monolayer that faces the cytosol
The concentration of actin monomers is high in the cytosol. What keeps these monomers from polymerizing totally into filaments? A. The concentration is high, but not high enough for polymerization to occur. B. The monomers are bound by proteins that prevent their polymerization. C. Not enough of the monomers are bound to ATP.
B. The monomers are bound by proteins that prevent their polymerization.
Which of the following scenarios requires an input of energy to occur? A. The movement of a solution 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 solution from a region of lower concentration on one side of a membrane to a region of higher concentration on the other side.
B. The movement of a solution from a region of lower concentration on one side of a membrane to a region of higher concentration on the other side.
Which molecule (or molecules) performs the primary signal transduction step in a signal transduction cascade? A. The extracellular signal B. The receptor protein C. The intracellular protein kinases
B. The receptor protein
Margarine is made from vegetable oils in which the hydrocarbon tails have had what treatment? A. Decreasing the number of single bonds (i.e., changing them to double bonds and removing hydrogen atoms) B. The removal of double bonds (i.e., changing them to single bonds and adding hydrogen atoms) C. The addition of carbon atoms D. The removal of carbon atoms
B. The removal of double bonds (i.e., changing them to single bonds and adding hydrogen atoms)
What is typically true of ion channels? A. They are open all the time. B. They are gated. C. They operate by active transport.
B. They are gated.
Which of the following mechanisms prevents osmotic swelling in plant cells? A. The collection of water in contractile vacuoles B. Tough cell walls C. The activity of Na+-K+ pumps
B. Tough cell walls
Myosins are motor proteins that use the energy of ATP hydrolysis to move along actin filaments. A. False B. True
B. True
Which molecule is displaced when a vesicle and its target membrane fuse? A. SNARES B. Water C. Phospholipids D. Cholesterol E. Tethering proteins
B. Water
Mutant Ras proteins, which are found in many cancer cells, can't hydrolyze their bound GTP to GDP, and therefore: A. can't turn themselves on. B. can't turn themselves off. C. can't be degraded. D. they are able to activate MAP kinase directly.
B. can't turn themselves off.
The hydrolysis of bound ATP to ADP in an actin filament _____ the strength of binding between monomers in the filament. A. increases B. decreases C. has no effect on
B. decreases
Following the binding of an extracellular signal molecule, receptor tyrosine kinases (RTKs) are activated by dimerization, which allows: A. each polypeptide chain in the dimer to phosphorylate itself on specific tyrosines in its cytoplasmic tail. B. each polypeptide chain to cross-phosphorylate the other chain in the dimer on specific tyrosines in its cytoplasmic tail. C. the receptor to be internalized so that it can phosphorylate and activate various intracellular signaling proteins.
B. each polypeptide chain to cross-phosphorylate the other chain in the dimer on specific tyrosines in its cytoplasmic tail.
The inside of a cell: A. is more positive than the outside of a cell. B. is more negative than the outside of a cell. C. has the same charge as the outside of the cell.
B. is more negative than the outside of a cell.
Nitric oxide (NO) causes blood vessels to dilate because: A. it causes endothelial cells lining blood vessels to relax. B. it causes smooth muscle cells in the walls of blood vessels to relax. C. it inhibits cyclic GMP production by inhibiting guanylyl cyclase. D. All of the above.
B. it causes smooth muscle cells in the walls of blood vessels to relax.
The movement of an ion down its electrochemical gradient is called: A. active transport. B. passive transport. C. osmosis. D. pumping.
B. passive transport.
Cells ingest large particles by: A. pinocytosis. B. phagocytosis. C. megacytosis.
B. phagocytosis.
( start of chapter 16 ) When cells respond to an extracellular signal, they most often convert the information from one form to another. This process is called: A. signal transformation. B. signal transduction. C. signal interference. D. signal amplification.
B. signal transduction.
In eukaryotic flagellum, the bending of microtubules is driven by: A. the basal body. B. the motor protein ciliary dynein. C. the fluid that surrounds the flagellum. D. actin and myosin.
B. the motor protein ciliary dynein.
When a vesicle fuses with the plasma membrane, the monolayer that was facing the inside of the vesicle will face: A. the cell cytoplasm. B. the outside of the cell.
B. the outside of the cell.
Ion-channel coupled receptors: A. transduce signals via elaborate intracellular signaling pathways. B. transduce signals in a simple and direct manner. C. integrate multiple signals at the same time. D. are voltage-gated.
B. transduce signals in a simple and direct manner.
Which of the following statements is NOT true regarding active transport? A. Some solutes are moved against their concentration gradients, from one side of a membrane to the other, using energy from ATP hydrolysis. B. Light-driven pumps couple the movement of solutes against their concentration gradient to an energy input from light. C. A coupled transporter brings two different types of solutes across the membrane, both moving from higher concentration to lower concentration.
C. A coupled transporter brings two different types of solutes across the membrane, both moving from higher concentration to lower concentration.
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? A. An endosome B. The Golgi apparatus C. A lysosome D. The endoplasmic reticulum E. A peroxisome
C. A lysosome
Which is NOT an integral membrane protein? A. A transmembrane protein that spans the lipid bilayer B. A monolayer associated protein tucked into the inner leaflet of the lipid bilayer C. A protein attached to the membrane by non-covalent interactions with other membrane proteins D. A lipid-linked protein anchored to the outer leaflet of the membrane
C. A protein attached to the membrane by non-covalent interactions with other membrane proteins
Ca2+ is an important intracellular messenger in which types of organisms? A. Animals B. Plants C. All eukaryotic organisms
C. All eukaryotic organisms
The drug taxol binds tightly to microtubules and prevents them from depolymerizing. The drug colchicine binds tightly to free tubulin and prevents its polymerization into microtubules. Which of these drugs arrests dividing cells in mitosis? A. Taxol B. Colchicine C. Both
C. Both
Prozac, among many other drugs, functions by altering neurotransmitter levels in the brain. How does Prozac work? A. By making serotonin-gated channel easier to open B. By increasing the amount of serotonin released from the presynaptic neuron, increasing the amount available in the synapses that use it C. By blocking the reuptake of serotonin after it has been released, 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
C. By blocking the reuptake of serotonin after it has been released, increasing the amount available in the synapses that use it
Which type of protein binds to improperly folded or improperly assembled proteins in the ER, holding them there until proper folding occurs? A. Tethering proteins B. Glycosylating proteins C. Chaperone proteins D. Antibody proteins
C. Chaperone proteins
The cell membrane is not involved in: A. cell communication B. import and export of molecules C. DNA replication D. cell growth and motility
C. DNA replication
Which of the following statements is true? A. Inside the cell the quantity of positively charged ions is greater than the quantity of negatively charged ions. B. Inside the cell the quantity of positively charged ions is less than the quantity of negatively charged ions. C. Inside the cell the quantity of positively charged ions is almost exactly equal to the quantity of negatively charged ions.
C. Inside the cell the quantity of positively charged ions is almost exactly equal to the quantity of negatively charged ions.
What is incorrect about a nerve impulse? A. It is another term for an action potential. B. It is electrical activity of the plasma membrane that is propagated rapidly along the membrane and sustained by automatic renewal along the way. C. It depends on the action of ligand-gated ion channels. D. It can travel at speeds of 100 meters per second.
C. It depends on the action of ligand-gated ion channels.
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 and stays open until the neurotransmitter detaches. B. It opens and then very quickly closes, triggering the neurotransmitter to detach. C. It flickers between open and closed states, but spends more time open while the neurotransmitter is bound.
C. It flickers between open and closed states, but spends more time open while the neurotransmitter is bound.
What is the name of the thin sheetlike structures that a fibroblast regularly extends during cell crawling? A. Pseudopods B. Filopodia C. Lamellipodia D. Phagosomes
C. Lamellipodia
Which of the following is true of lysosomes? A. The products of digestion in lysosomes leave the lysosome by transport vesicles. B. Most of the lysosomal membrane proteins have glycosylated regions on the cytosolic side of the membrane. C. Lysosomal enzymes are optimally active in the acidic conditions maintained within lysosomes. D. Lysosomes form from vesicles that pinch off from the endoplasmic reticulum.
C. Lysosomal enzymes are optimally active in the acidic conditions maintained within lysosomes.
Lipid bilayers are highly impermeable to: A. carbon dioxide. B. water. C. Na+ and Cl-. D. ethanol.
C. Na+ and Cl-.
Which of the following types of intermediate filaments are found in all animal cells? A. Keratins B. Vimentin and vimentin-related filaments C. Nuclear lamins D. Neurofilaments
C. Nuclear lamins
Which type of receptors do steroid hormones employ? A. Cell-surface receptors B. Ion-channel-coupled receptors C. Nuclear receptors
C. Nuclear receptors
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, glucose, oxygen F. Sodium ions, oxygen, glucose
C. Oxygen, glucose, sodium ions
Auditory hair cells in the ear depend on what type of ion channel to detect sound vibrations? A. Voltage-gated B. Ligand-gated C. Stress-gated
C. Stress-gated
Which organelle receives proteins and lipids from the endoplasmic reticulum, modifies them, and then dispatches them to other destinations in the cell? A. A mitochondrion B. An endosome C. The Golgi apparatus D. The nucleus E. A peroxisome
C. The Golgi apparatus
Which does NOT contain actin and myosin? A. A muscle cell sarcomere B. The contractile ring that carries out cytokinesis C. The filopodium at the leading edge of a crawling cell D. A contractile bundle in a nonmuscle cell
C. The filopodium at the leading edge of a crawling cell
Which of the following inhibits ions from passing through a lipid bilayer? A. The watery environment on either side of the lipid bilayer B. The hydrophilic exterior of the lipid bilayer C. The hydrophobic interior of the lipid bilayer
C. The hydrophobic interior of the lipid bilayer
Which of the following statements is NOT true of mitochondrial proteins that are synthesized in the cytosol? A. The proteins are unfolded as they are transported into the mitochondria. B. The proteins cross both the inner and outer mitochondrial membranes as they are imported. C. The proteins are transported across the mitochondrial membranes while being synthesized. D. Chaperone proteins help draw the proteins inside the mitochondrion. E. The proteins usually have a signal sequence at their N-terminus.
C. The proteins are transported across the mitochondrial membranes while being synthesized.
Which organelle sequesters Ca2+ inside muscle fibers? A. The nucleus B. Mitochondria C. The sarcoplasmic reticulum D. The Golgi apparatus E. Lysosomes
C. The sarcoplasmic reticulum
Which of the following is NOT a role for the oligosaccharides on glycosylated proteins? A. They can protect the protein from degradation and hold it in the ER until it is properly folded. B. They can guide the protein to the appropriate organelle by serving as a transport signal for packaging the protein into appropriate transport vesicles. C. They can provide a source of energy for the cell. D. When displayed on the cell surface, oligosaccharides form part of the cell's carbohydrate layer and can function in the recognition of one cell by another.
C. They can provide a source of energy for the cell.
( start of chapter 17 ) Which of the following is the main function of intermediate filaments? A. To provide tracks for guiding intracellular transport B. To enable cells to crawl C. To enable cells to withstand the mechanical stress that occurs when cells are stretched
C. To enable cells to withstand the mechanical stress that occurs when cells are stretched
How does Diacylglycerol (DAG) function in the inositol phospholipid pathway? A. It activates phospholipase C. B. On its own, it recruits and activates protein kinase C (PKC). C. Together with Ca2+, it recruits PKC from the cytosol to the plasma membrane and activates it. D. It binds to and opens Ca2+ channels in the plasma membrane, allowing extracellular Ca2+ to enter the cytosol.
C. Together with Ca2+, it recruits PKC from the cytosol to the plasma membrane and activates it.
In eukaryotic cells, the cell cortex is made of: A. a network of intermediate filaments. B. a network of microtubules. C. a network of actin filaments.
C. a network of actin filaments.
Inhibitory neurotransmitters such as glycine and GABA make a postsynaptic cell harder to depolarize by: A. allowing an influx of Na+. B. allowing Na+ to escape. C. allowing an influx of Cl-. D. allowing an influx of K+.
C. allowing an influx of Cl-.
The entire phospholipid molecule is: A. hydrophobic B. hydrophilic C. amphipathic
C. amphipathic
When activated by the binding of Ca2+, calmodulin relays the Ca2+ signal onward by undergoing a conformational change and then: A. binding to various extracellular proteins and directly activating them. B. transferring its bound Ca2+ to various intracellular proteins, thereby activating them. C. binding to Ca2+-calmodulin-dependent protein kinases (CaM-kinases), which then phosphorylate other intracellular proteins. D. binding to cyclic AMP.
C. binding to Ca2+-calmodulin-dependent protein kinases (CaM-kinases), which then phosphorylate other intracellular proteins.
The low pH inside endosomes: A. destroys internalized cargo proteins. B. destroy internalized receptors. C. causes internalized receptors to release their cargo. D. causes cargo proteins to bind to their receptors.
C. causes internalized receptors to release their cargo.
The shape of a cell and the mechanical properties of its plasma membrane are determined by a meshwork of fibrous proteins called: A. basal lamina. B. carbohydrate layer. C. cell cortex. D. tight junction.
C. cell cortex.
Channelrhodopsin can be used to manipulate the activity of neurons because: A. channelrhodopsin and neurons are both sensitive to light. B. channelrhodopsin, when activated by light, polarizes the membrane and stimulates neurons. C. channelrhodopsin, when activated by light, depolarizes the membrane and stimulates neurons. D. channelrhodopsin is a natural component of excitatory neurons.
C. channelrhodopsin, when activated by light, depolarizes the membrane and stimulates neurons.
When activated by a GPCR, adenylyl cyclase: A. converts AMP to cAMP. B. converts ADP to cAMP. C. converts ATP to cAMP. D. converts cyclic AMP to AMP.
C. converts ATP to cAMP.
Most extracellular signal molecules act on cell-surface rather than intracellular receptors because they are: A. too large to pass directly across the plasma membrane. B. too hydrophilicto pass directly across the plasma membrane. C. either too large, too hydrophilic, or both to pass directly across the plasma membrane.
C. either too large, too hydrophilic, or both to pass directly across the plasma membrane.
Eukaryotic cells continually ingest bits of their plasma membrane, along with small amounts of extracellular fluid. The lost pieces of membrane are replaced by the process of: A. pinocytosis. B. phagocytosis. C. exocytosis. D. endocytosis.
C. exocytosis.
The ER signal sequence on a growing polypeptide chain is recognized by a signal recognition particle (SRP) in the cytosol. This interaction: A. causes the polypeptide chain to dissociate from the ribosome. B. causes the ribosome to return to the pool of free ribosomes in the cytosol. C. guides the ribosome and its polypeptide to the ER membrane. D. speeds the synthesis of the polypeptide chain.
C. guides the ribosome and its polypeptide to the ER membrane.
Microtubules are: A. rope-like strands. B. mesh-like networks. C. hollow tubes. D. interlocking chains.
C. hollow tubes.
Nitric oxide (NO) acts only on neighboring cells (as a local mediator in paracrine signaling) because: A. so little is produced by the signaling cell. B. it is rapidly washed away by the blood stream. C. it is rapidly converted to nitrates and nitrites in the extracellular fluid. D. it is rapidly converted to nitrates and nitrites in the target cell.
C. it is rapidly converted to nitrates and nitrites in the extracellular fluid.
The voltage difference across a membrane of a cell is called the: A. electrical potential. B. electrical current. C. membrane potential. D. potential energy.
C. membrane potential.
The long fibers of a skeletal muscle are: A. many cells organized end-to-end. B. one large cell with a single nucleus. C. one large cell with many nuclei.
C. one large cell with many nuclei.
Intermediate filaments are: A. tubelike structures. B. springlike structures. C. ropelike structures. D. meshlike structures.
C. ropelike structures.
RTKs can activate the enzyme phosphoinositide 3-kinase, which phosphorylates inositol phospholipids. These phospholipids then: A. serve as phosphate donors in phosphorylation reactions. B. activate Ras. C. serve as docking sites that recruit specific intracellular signaling proteins to the plasma membrane. D. activate G proteins.
C. serve as docking sites that recruit specific intracellular signaling proteins to the plasma membrane.
Dynamic instability is: A. the ability of a microtubule to shrink rapidly during mitosis. B. the ability of a microtubule to grow rapidly during meiosis. C. the ability of a microtubule to switch back and forth between polymerization and depolymerization. D. the ability of a microtubule to switch polarity back and forth between a positive and negative charge.
C. the ability of a microtubule to switch back and forth between polymerization and depolymerization.
The direction that glucose is transported across the membrane is determined by: A. the electrochemical gradient. B. the membrane potential. C. the concentration gradient. D. the molecule's charge.
C. the concentration gradient.
Many proteins are glycosylated in: A. the cytosol. B. mitochondria. C. the endoplasmic reticulum. D. lysosomes. E. peroxisomes.
C. the endoplasmic reticulum.
Proteins in the cytosol that are destined for other organelles must first enter the: A. the nucleus. B. the Golgi apparatus. C. the endoplasmic reticulum. D. the lysosomes.
C. the endoplasmic reticulum.
Osmosis can be described as: 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 water concentration to an area of high water concentration. C. the movement of water from an area of low solute concentration to an area of high solute concentration. D. the movement of water from an area of low solvent concentration to an area of high solvent concentration.
C. the movement of water from an area of low solute concentration to an area of high solute concentration.
A target cell can respond quickly to an extracellular signal if: A. the cell does not require a receptor for the signal molecule. B. the response does not require target cell proteins to be altered. C. the response does not require new gene transcription or new protein synthesis.
C. the response does not require new gene transcription or new protein synthesis.
In a centrosome, which structures serve as nucleation sites for the formation of microtubules? A. Tubulin protofilaments B. /alpha/beta-tubulin dimers C. /alpha- and /beta-tubulin monomers D. /gamma-tubulin rings
D. /gamma-tubulin rings
What do carbohydrates attached to cell-surface proteins and lipids provide a cell? A. Protection from mechanical and chemical damage B. A slimy coat that prevents cells from sticking to one another C. A distinctive identity in cell-cell recognition D. All of the above
D. All of the above
What does a target cell require to respond to an extracellular signal molecule? A. Access to the signal molecule B. The presence of an appropriate receptor for the signal molecule C. Appropriate intracellular signaling pathways D. All of the above
D. All of the above
Which of the following pathways is activated by most RTKs? A. The phosopholipase C/inositol phospholipid signaling pathway B. The Ras signaling pathway C. MAP-kinase signaling module D. All of the above E. None of the above
D. All of the above
Which of the following is NOT true of receptor-mediated endocytosis? A. In receptor-mediated endocytosis, extracellular substances are internalized in clathrin-coated vesicles. B. Low-density lipoproteins (LDLs) are taken into cells by receptor-mediated endocytosis. C. Some viruses are taken into the cell by receptor-mediated endocytosis. D. In receptor-mediated endocytosis, internalized vesicles fuse with lysosomes, which then mature into endosomes.
D. In receptor-mediated endocytosis, internalized vesicles fuse with lysosomes, which then mature into endosomes.
As a cell grows, which microtubule-associated protein pulls the ER membrane outward, stretching it like a net? A. Dynein B. Cohesin C. Actin D. Kinesin
D. Kinesin
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? A. Glycosylate the misfolded protein B. Increase the transport of misfolded proteins to the Golgi apparatus C. Export the misfolded proteins to the cytosol D. Produce more ER
D. Produce more ER
Mitochondria and peroxisomes do NOT have what in common? A. Their membranes contain a protein translocator. B. They are present in eukaryotic cells. C. They must import proteins to function. D. Proteins need to unfold to enter them.
D. Proteins need to unfold to enter them.
Which of the following activities restores the ion gradients across the plasma membrane of an axon after an action potential has occurred? A. The opening of voltage-gated Na+ channels B. The opening of voltage-gated K+ channels C. The activity of K+ leak channels D. Pumping by the Na+/K+ ATPase
D. Pumping by the Na+/K+ ATPase
Which organelle is important for controlling the concentration of calcium ions in the cytosol? A. The Golgi apparatus B. The nucleus C. Lysosomes D. The endoplasmic reticulum
D. The endoplasmic reticulum
GPCRs are often referred to as seven-pass transmembrane receptors because they have: A. seven pores that signal molecules can use to pass through the bilayer. B. seven receptors on each side of the lipid bilayer that receive and transmit signals. C. seven different G proteins with which they interact to amplify signals. D. a polypeptide chain that crosses the lipid bilayer seven times.
D. a polypeptide chain that crosses the lipid bilayer seven times.
Myosin-I is present in: A. nerve cells only. B. muscle cells only. C. epithelial cells only. D. all types of cells.
D. all types of cells.
Keratins are NOT found in: A. hair. B. reathers. C. the tongue. D. bones.
D. bones.
Ras is activated by a Ras-activating protein that: A. causes Ras to bind to a G protein. B. phosphorylates Ras. C. dephosphorylates Ras. D. causes Ras to exchange GDP for GTP.
D. causes Ras to exchange GDP for GTP.
Many drugs act by binding to: A. protein kinases. B. cyclic AMP. C. nuclear receptors. D. cell surface receptors.
D. cell surface receptors.
The enzyme cyclic AMP phosphodiesterase helps terminate a response mediated by an increase in cyclic AMP by: A. converting AMP to cyclic AMP. B. converting cyclic AMP to ATP. C. converting ATP to cyclic AMP. D. converting cyclic AMP to AMP.
D. converting cyclic AMP to AMP.
Phagocytic cells include: A. neutrophils and red blood cells. B. red blood cells and liver cells. C. protozoa and bacteria. D. macrophages and neutrophils.
D. macrophages and neutrophils.
Another name for small messenger molecules is: A. first messengers. B. intracellular signaling proteins. C. extracellular signals. D. second messengers.
D. second messengers.
The phosphorylated tyrosines on activated RTKs: A. (A) help activate the kinase activity of the receptor. B. (B) serve as binding sites for G proteins. C. (C) serve as binding sites for a variety of intracellular signaling proteins. D. All of the above E. A and C
E. A and C
Which component or components of a G protein can, on its own, activate downstream proteins in an intracellular signaling pathway? A. (A) /alpha subunit B. (B) /beta subunit C. (C) /beta/gamma complex D. All of the above E. A and C
E. A and C
Which organelle contains enzymes used in a variety of oxidative reactions that break down lipids and destroy toxic molecules? A. A mitochondrion B. An endosome C. A lysosome D. The endoplasmic reticulum E. A peroxisome
E. A peroxisome
Which proteins play a central role in the fusion of a vesicle with a target membrane? A. Rab proteins B. Tethering proteins C. Adaptin proteins D. Clathrin proteins E. SNARE proteins
E. SNARE proteins