cellular molecular biology exam 3
Which of the following transport processes occurs via vesicular transport? A. import into the nucleus B. import into the chloroplast C. import into the mitochondria D. import into the ER E. import into the Golgi
import into the Golgi
Which of the following is not imported into the ER? proteins destined for the ER lumen proteins destined for the Golgi lumen proteins destined for the mitochondria proteins destined for the plasma membrane proteins destined for secretion
proteins destined for the mitochondria
Following transport of a protein into the mitochondria, the signal sequence is removed by a protein called a ________________.
signal peptidase
Which of the following is not required for nuclear import? A. nuclear localization signal (NLS) B. cytosolic fibrils on proteins present in nuclear pore C. nuclear import receptor D. signal recognition particles E. energy input
signal recognition particles
Which of the following methods does not require any transporter or channel for transport of substances? A. active transport B. facilitated diffusion C. simple diffusion
simple diffusion
Which of the following is not needed for nuclear import? a. nuclear localization signal (NLS) b. nuclear pore c. nuclear import receptor d. protein translocator
D
Which of the following is not part of the endomembrane system? A. nuclear membrane B. plasma membrane C. ER membrane D. mitochondrial membrane E. Golgi membrane
D
Which of the following statements about transporters is false? a. They are single pass transmembrane proteins. b. They undergo conformation changes as molecules are transported across the membrane. c. They are selective and possess binding sites for specific molecules. d. They can move a solute against its electrochemical gradient. e. They transport molecules relatively slowly across the membrane.
A
Which of the following processes is part of the secretory pathway? A. :import into the nucleus B. import into the chloroplast C. transport from the ER to the nucleus D. transport from the Golgi to the plasma membrane E. transport from the mitochondria to the plasma membrane
D
Transporters, in contrast to channels, work by _____________. a. specific binding to solutes b. a gating mechanism c. filtering solutes by charge d. filtering solutes by size
A
What is the role of the signal recognition particle (SRP)? a. binds to an ER signal sequence b. binds to a vesicle coat protein c. binds to a tethering protein and aids in vesicle docking d. binds to a nuclear localization signal e. binds to a protein translocator in the ER membrane
A
Which of the following proteins is not required for vesicle docking? a. cargo receptors b. tethering proteins c. Rabs d. v-SNARES e. t-SNARES
A
. Secretory proteins are synthesized on ____________. a. ribosomes on endoplasmic reticulum b. free ribosomes in the cytosol c. ribosomes in the mitochondria d. ribosomes on the nuclear envelop
A
Fill in the blank in the signaling pathway below: extracellular signal -> RTK -> phospholipase C -> IP3 + DAG -> __________ -> transcription regulator -> change in gene expression a. PKC (protein kinase C) b. Ca2+ c. adenylyl cyclase d. MAP kinase e. calmodulin
A
Nuclear localization signals that ensure transport of a protein to the nucleus are rich in _______. a. Lysine (K) and Arginine (R) b. Glutamine (E) and Asparagine (N) c. Serine (S) and Threonine (T) d. Tryptophan (W) and Histidine (H)
A
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. by secreting hormones and other small signaling molecules D.none of the above
A
These proteins bind to both the coat protein and the cargo receptor. A. adaptins B. tethering proteins C. clathrin D. dynamin E. v-SNARES
A
Which of the following statements about vesicle budding from the golgi apparatus is false? a. Clathrin molecules are important for binding and selecting cargoes for transport. b. Adaptins interact with clathrin. c. Once vesicle budding occurs, clathrin molecules are released from the vesicle. d. Clathrin molecules act at the cytosolic surface of the golgi apparatus e. Vesicles leaving the trans golgi network can fuse with the early endosome or the plasma membrane
A
Which of the following statements about vesicular membrane fusion is false? A. Membrane fusion always immediately follows vesicle docking. B. The surfaces of membranes have water molecules associated with them that must be displaced before vesicle fusion can occur. C. Vesicle fusion results in the addition of vesicle membrane to the target membrane. D. The interactions of the v-SNAREs and the t-SNAREs pull the vesicle membrane and the target organelle membrane together so that their lipids can intermix.
A
Which of the following statements is false? A. The accumulation of misfolded proteins in the Golgi leads to a program called the unfolded protein response (UPR). B. Proteins that are misfolded will not leave the ER. C. The UPR triggers the production of transcription factors that will activate the expression of genes encoding chaperones. D. Protein synthesis is slowed down during the UPR. E. Apoptosis can occur if there is there is continued accumulation of misfolded proteins.
A
Which of the following statements is true? a. Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior. b. To function, all extracellular signal molecules must be transported by their receptors across the plasma membrane into the cytosol. c. A cell-surface receptor capable of binding only one type of signal can mediate only one kind of response. d. Changes in gene expression are a very fast cellular response to activation of a signaling pathway.
A
Signal sequences that direct proteins to the correct compartment are ____________. a. added to proteins through post-translational modifications b. added to a protein by a protein translocator c. encoded in the amino acid sequence and sufficient for targeting a protein to its correct destination d. always removed once a protein is at the correct destination
C
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. Oxygen, glucose, sodium ions c. Oxygen, sodium ions, glucose d. Sodium ions, glucose, oxygen e. Sodium ions, oxygen, glucose
B
The Na+ /Ca2+ exchanger, which couples the movement of Na+ down its electrochemical gradient with the movement of Ca2+ against its electrochemical gradient, is a(n) _____________ because Ca2+ and Na+ move in different directions across the membrane. a. uniport b. antiport c. symport d. cisport
B
A cell secretes growth factors that have a slow diffusion rate, and interacting only with other cells in the immediate area is an example of _______________ signaling. a. endocrine b. paracrine c. neuronal d. contact-dependent
B
Identify the correct sequence of cell signaling events. a. activation of cellular response, reception, transduction b. reception, transduction, activation of cellular response c. transduction, reception, activation of cellular response d. reception, activation of cellular response, transduction
B
Particle A is observed to be brought into the cell through endocytosis. This means that the destination of particle A is most likely ___________. a. the cytosol because it is being transported via a vesicle b. one of the membrane-bound organelles because it is being transported via a vesicle c. the cytosol because vesicles aren't involved d. one of the membrane-bound organelles because vesicles aren't involved
B
Proteins moving along the secretory pathway exit the ER via vesicular transport and next move to the: A. trans face of the Golgi B. cis face of the Golgi C.plasma membrane D. early endosome E.nucleus
B
Proteins that are not intended to remain in the endoplasmic reticulum move onward to the golgi apparatus, where further modification and protein sorting occurs. How do proteins generally move between these different compartments? a. via protein translocators b. via vesicular traffic c. via receptor proteins d. via protein carriers e. via protein translocators
B
The growth factor RGF stimulates proliferation of cultured rat cells. The receptor that binds RGF is a receptor tyrosine kinase called RGFR. Which of the following types of alteration would be most likely to prevent receptor dimerization? a. a mutation that increases the affinity of RGFR for RGF b. a mutation that prevents RGFR from binding to RGF c. mutations that change the tyrosines that are normally phosphorylated on RGFR dimerization to alanines d. none of the above
B
The mitogen-activated protein (MAP) kinase cascade triggered by RTKs results in cell division. Which of the following scenarios would likely lead to uncontrolled cell proliferation? a. loss of function mutation in MAPK b. mutant Ras protein unable to hydrolyze its bound GTP c. mutant Ras protein unable to interact and activate MAPKKK d. none of the above
B
The outer membrane of the nuclear envelope is continuous with the membrane of which other part of the cell? A. mitochondrion B. endoplasmic reticulum C. Golgi apparatus D. lysosome E. endosome
B
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
When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is a _____________. a. neurotransmitter b. hormone c. local mediator d. second messenger
B
Which molecules are displaced when a vesicle and its target membrane fuse? A. SNARES B. water molecules C.phospholipids D. tethering proteins E.Rabs
B
Which of the following is not a means by which cells drive active transport? a. The uphill transport of a solute is coupled to ATP hydrolysis. b. The uphill transport of a solute is coupled to movement of ATP across a membrane. c. The uphill transport of a solute is coupled to an input of energy from light. d. The uphill transport of a solute is coupled to the downhill transport of a second solute.
B
Which of the following plasma membrane receptors activate signaling pathways by forming molecular dimers that result in protein phosphorylation reactions upon binding of their specific ligand? a. nuclear receptors b. receptor tyrosine kinases c. ligand-gated ion channels d. G protein-coupled receptors
B
Which of the following statements about GPCR signaling is false? a. GPCRs contain 7 transmembrane helices. b. Activated G proteins can activate cytosolic enzymes and ion channels. c. A trimeric G protein has three subunits: alpha, beta, and gamma and the alpha and gamma subunits are associated with the plasma membrane. d. Binding of a ligand to a GPCR results in a conformational change in the GPCR.
B
Which of the following statements about membrane transport is false? a. The Na+ outside a mammalian cell is much higher than that inside the cell. b. Transport of an ion across a membrane depends on only its concentration gradient. c. Transporters can perform both passive and active transport. d. Passive transport occurs spontaneously and does not require an input of energy. e. Membrane potential refers to the difference in the electrical potential on one side of the membrane versus the other.
B
Which of the following statements about molecular switches is true? a. Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off. b. Protein kinases transfer the terminal phosphate from ATP to a protein. c. Protein kinases transfer the terminal phosphate from ATP onto GDP to form GTP. d. A GTP-binding protein exchanges its bound GTP for GDP to become activated.
B
Which of the following statements about protein glycosylation is false? a. N-linked glycosylation adds a oligosaccharide to the nitrogen atom of asparagine. b. Glycosylation starts in the ER and continues in the cytosol. c. A preformed branch oligosaccharide, attached to a lipid called dolichol in the ER membrane, is transferred to a protein. d. Glycosylation is the covalent attachment of a short oligosaccharide to a protein
B
Which of the following statements about the glucose transporter is false? a. It is a uniporter. b. It performs active transport. c. It can transport glucose either into or out of cells. d. The net flow of glucose is determined solely by the concentration of glucose on either side of the membrane.
B
In paracrine signaling, signal molecules called _____________________ act in the neighborhood of the signaling cells. A.hormones B. neurotransmitters C. local mediators D. G proteins E. second messengers
C
Which of the following statements about transport into mitochondria is false? a. The signal sequence on proteins destined for mitochondria is recognized by a receptor protein in the outer membrane. b. After a protein moves through the protein translocator in the outer membrane, the protein diffuses in the inner membrane space until it encounters a protein translocator in the inner membrane. c. Proteins that are transported into mitochondria are unfolded as they are being transported. d. Signal peptidase will remove the signal sequence once the protein has been imported
B
In which of the following steps does amplification not occur. a. phosphorylation of transcription regulators by an active kinase b. activation of G proteins by an activated GPCR c. activation of an enzyme by a G protein d. production of cAMP from adenylyl cyclase
B Or c
. Import into which of the following cell compartments does not require protein unfolding? a. chloroplasts b. ER c. nucleus d. mitochondria
C
A signal outside the cell is detected by specific receptors and converted to a signal inside the cell that alters cellular behavior; this conversion is called _____________. A.signal amplification B. signal transversion C. signal transduction D.signal integration
C
The first step in N-linked protein glycosylation: A. takes place in the Golgi and involves the addition of single glucose molecule to an asparagine side chain B. takes place in the Golgi and involves the addition of a branched oligosaccharide to an asparagine side chain C. takes place in the ER and involves the addition of a branched oligosaccharide to an asparagine side chain D. takes place in the ER and involves the addition of a single glucose molecule to an asparagine side chain
C
The retention signal of proteins of endoplasmic reticulum consists of _________. a. Gly-Asp-Glu-Leu (GDEL) at the N-terminus b. Gly-Asp-Glu-Leu (GDEL) at the C-terminus c. Lys-Asp-Glu-Leu (KDEL) at the N-terminus d. Lys-Asp-Glu-Leu (KDEL) at the C-terminus
C
Transporter proteins and ion channels function in membrane transport by providing a ____________ pathway through the membrane for specific polar solutes or inorganic ions. a. hydrophobic b. amphipathic c. hydrophilic d. passive e. none of the above
C
Which of the following is a monomeric GTPase that acts as a molecular switch and is in the active state when bound to GTP? a. Raf b. kinase c. Ras d. Rab
C
Which of the following is not a second messenger important in the inositol phospholipid pathway? a. IP3 b. DAG (diacylglycerol) c. cAMP d. Ca2+
C
Which of the following is not needed for import of proteins into the ER? a. ER signal sequence b. protein translocator c. import receptor protein d. signal recognition particle (SRP) e. SRP receptor
C
Which of the following lists the general steps of a signaling pathway in the correct order? 1 receptor generates an intracellular signal 2. cellular response such as an alteration in metabolism 3. an effector protein such as an enzyme is activated 4. extracellular signal binds to a receptor 5. message is passed from one intracellular signaling molecule to another a. 1, 2, 3, 4, 5 b. 1, 4, 5, 3, 2 c. 4, 1, 5, 3, 2 d. 2, 4, 1, 5, 3 e. 4, 5, 1, 3, 2
C
Which of the following statements about heterotrimeric G proteins is false? a. The alpha and gamma subunits have lipid tails that tether them to the membrane. b. The G protein is activated when the alpha subunit exchanges GDP for GTP. c. Upon activation, the beta subunit dissociates from the alpha/gamma complex. d. The alpha subunit has an intrinsic GTP hydrolysis activity. e. Active G proteins bind to and activate membrane ion channels and enzymes.
C
Which of the following statements about ion channels is false? a. Channels are transmembrane proteins. b. Channels discriminate solutes based on size and charge. c. Channels can perform active transport. d. Channels can be gated which means they can exist in either an open or closed conformation. e. The narrowest part of a channel is called the selectivity filter.
C
Which of the following statements related to protein sorting is false? a. Subcellular localization is an integral part of protein functionality. b. Many proteins exhibit functions only after being transported to certain compartments of the cell. c. All proteins exhibit functions after being transported to certain compartments of the cell. d. Protein sorting is also known as protein targeting.
C
Which of the following types of signaling involves membrane-bound signal molecules? A.endocrine B. paracrine C. contact-dependent D. neuronal/synaptic E.all of the above
C
You have a cell line that expresses a GPCR, the corresponding G protein, and adenylyl cyclase. Which of the following mutations would increase the intracellular levels of cAMP upon addition of the GPCR ligand? a. A mutation in the GPCR that prevents G protein activation. b. A mutation in the alpha subunit of the G protein that prevents it from releasing bound GDP. c. A mutation in the alpha subunit of the G protein that prevents GTP hydrolysis. d. A mutation in the GPCR that prevents it from binding the ligand
C
Your friend has just joined a lab that studies vesicle budding from the Golgi and has been given a cell line that does not form mature vesicles. This cell line forms coated pits but vesicle budding and the removal of coat proteins don't happen. Which of the following proteins might be lacking in this cell line? a. clathrin b. Rab c. dynamin d. tethering proteins
C
which of the following statements is false? A. During exocytosis, vesicles from the Golgi fuse with the plasma membrane. B. Vesicles from the trans Golgi network can fuse with either the early endosome or the plasma membrane. C. The cis-face of the Golgi faces the plasma membrane and the trans-face is adjacent to the ER. D. Secreted proteins often have disulfide bonds or are glycosylated. E. The Golgi apparatus is important for further modifications of oligosaccharide groups on proteins.
C
Which of the following molecules would exhibit the fastest rate of transport across a membrane?
CO2
All of the following are true of calmodulin except it can interact with many different target proteins it undergoes a conformational change upon Ca2+ binding the overall tertiary structure resembles a dumb-bell Calmodulin binds to CaM kinases and inactivates them.
Calmodulin binds to CaM kinases and inactivates them.
All of the following are true of calmodulin except Calmodulin binds to CaM kinases and inactivates them. it can interact with many different target proteins it undergoes a conformational change upon Ca2+ binding the overall tertiary structure resembles a dumb-bell
Calmodulin binds to CaM kinases and inactivates them.
All of the following are true of calmodulin except Calmodulin binds to CaM kinases and inactivates them. the overall tertiary structure resembles a dumb-bell it can interact with many different target proteins it undergoes a conformational change upon Ca2+ binding
Calmodulin binds to CaM kinases and inactivates them.
A cell releases chemical signals into its surrounding space in order to communicate with neighboring cells. Which of the following must occur for the communication to be successful? A. The chemical signal must bind to hormones on the neighboring cells. B. The same chemical signal must be produced within the neighboring cells. C. The neighboring cells must be able to absorb the chemicals through diffusion. D. The neighboring cell must have the right receptor to perceive the signal.
D
During nervous-system development in Drosophila, the membrane-bound protein Delta acts as an inhibitory signal to prevent neighboring cells from developing into neuronal cells. Delta is involved in __________ signaling. a. endocrine b. paracrine c. neuronal d. contact-dependent
D
Place the following events in their sequential order: 1. protein kinase A is activated 2. glycogen breakdown 3. epinephrine binds to G-protein-coupled receptor 4. G-protein activates adenylyl cyclase 5. GTP is exchanged for GDP on the G-protein 6. ATP is converted to cAMP a. 1, 3, 5, 4, 6, 2 b. 3, 5, 4, 1, 6, 2 c. 3, 4, 5, 1, 6, 2 d. 3, 5, 4, 6, 1, 2
D
Signal sequences are ___________. a. short peptide sequences to transport a protein to the nucleus b. glycoproteins that serve as an address for transporting newly synthesized proteins to their correct cellular location c. short peptide sequences that target a protein for degradation d. short peptide sequences that serve as an address for transporting newly synthesized proteins to their correct cellular location
D
These proteins assemble as a ring around the neck of a budding vesicle and are important for vesicles to pinch off from the membrane. A. adaptins B. Rabs C. clathrin D.dynamin E. v-SNARES
D
What would happen to the location of a protein in which you replaced the hydrophobic amino acids of an ER signal sequence with amino acids that do not correspond to a sorting signal? a. The protein would be targeted to the ER. b. The protein would be secreted from the cell. c. The protein would enter the Golgi lumen. d. The protein would remain in the cytosol.
D
Which of the following choices reflects the appropriate order of locations through which a secretory protein travels? a. lysosome -->endosome --> plasma membrane b. ER--> lysosome--> plasma membrane c. Golgi ---> lysosome--> plasma membrane d. ER ---> Golgi--> plasma membrane e. Golgi ---> ER---> plasma membrane
D
Which of the following statements about membrane transport is false? a. The transport of an ion across a membrane depends on both its concentration gradient and the membrane potential. b. The Na+ concentration of an animal cell is much higher outside the cell as compared with the inside of the cell. c. The K+ concentration of an animal cell is much higher inside the cell as compared with outside the cell d. The Na+ /K+ pump moves one Na+ out of the cell and one K+ into the cell. e. The Na+ /K+ pump couples the uphill transport of Na+ and K+ with the hydrolysis of ATP
D
Which of the following statements about the unfolded protein response (UPR) is false? a. The UPR regulates protein quality control in the ER. b. The UPR is activated when unfolded proteins accumulate in the ER. c. Proteins that are not folded correctly do not leave the ER. d. Misfolded proteins in the ER activate the UPR by activating proteins in the ER lumen.
D
Which of the following statements is false? a. The Na+ concentration is higher outside animal cells than inside the cell. b. The K+ concentration is higher inside animal cells than outside the cell. c. The Na+ /K+ pump is an ATP driven pump that pumps Na+ outside the cell and K+ inside the cell. d. The glucose-Na+ symport pumps Na+ outside the cell while glucose goes down its concentration gradient.
D
Which of the following proteins is not required for vesicle formation and cargo selection? a. clathrin b. dynamin c. adaptins d. cargo receptors e. Rabs
E
Which of the following proteins is required for vesicle fusion? a. tethering proteins b. Rabs c. v-SNARES d. t-SNARES e. both c and d
E
all of the following are aims of the unfolded protein response except: A. inhibition of translation B. increased expression of transcription regulators C. increased expression of chaperones D. production of more ER E. increased production of ribosomes
E
Which of the following sorting signals would be present in a soluble protein destined for the Golgi lumen?
ER signal sequence
Listed below are events that occur during a signal transduction pathway. I. The plasma membrane receptor activates an intracellular signaling molecule. II. There is a change in gene expression in the cell. III. Ligand binds to the plasma membrane receptor. IV. Effector protein (transcription factor) is activated. Which of the following lists these events in the correct order?
III, I, II, IV
Which second messenger signals the release of Ca+2 from endoplasmic reticulum in the inositol phospholipid pathway? IP3 DAG cAMP cGMP
IP3
Extracellular signal --> G protein coupled receptor --> G protein --> phospholipase C --> ______________ --> protein kinase C (PKC). Ras adenyl cyclase MAPKKK cAMP IP3 and DAG
IP3 and DAG
Which of the following statements about ion channels is false? A. The narrowest part of an ion channel is called the selectivity filter. B. Ion channels are not very selective. C. An ion channel lined with positively charged amino acids will transport negative ions. D. Ion channels have a faster rate of transport compared with transporters.
Ion channels are not very selective.
______________ transfer the terminal phosphate group from ATP to substrate proteins while _______________remove phosphate groups from substrates. Phosphatases, phospholipase C Kinases, phosphatases Phosphatases, kinases Calmodulin, phosphatases none of the above
Kinases, phosphatases
Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell. Which of the following ions is the most abundant inside a typical mammalian cell? Na+ K+ Ca2+ Cl−
K+
Active transport requires the input of energy into a system so as to move solutes against their electrochemical and concentration gradients. Which of the following is NOT one of the common ways to perform active transport?
K+-coupled
The signal that is important for retention of proteins in the lumen of the ER is called the: nuclear localization sequence (NLS) stop transfer sequence start transfer sequence KDEL (LysAspGluLeu) none of the above
KDEL (LysAspGluLeu)
Which component of a MAPK phosphorylation cascade phosphorylates and directly activates transcription regulators? MAPKKK MAPKK MAPK Ras
MAPK
Which component of a MAPK phosphorylation cascade phosphorylates is directly activated by Ras? MAPKKK MAPKK MAPK RTK
MAPKKK
Which of the following statements about cell signaling is false? A cell must have a receptor for a particular signal in order to respond to that signal. Most signals bind to intracellular receptors. The combination of signals that a cell perceives determines the cellular response. A transcription regulator is an example of an effector protein that brings about a cellular response. Kinases are often organized into phosphorylation cascades.
Most signals bind to intracellular receptors.
If ATP hydrolysis is inhibited, which of the following types of movement across a cell membrane would likely also be inhibited? Movement of a substance from an area of lower concentration to an area of higher concentration. Movement of water through water channels called aquaporins, which facilitate the diffusion of water across a membrane. Facilitated diffusion of ions through channels. Passage of glucose across a membrane by passive transport.
Movement of water through water channels called aquaporins, which facilitate the diffusion of water across a membrane.
Which of the following proteins is responsible for generating the Na+ gradient across the plasma membrane of animal cells?
Na+/K+ pump
The __________ is an ATP driven pump; the ___________is a gradient-driven pump.
Na+/K+ pump; glucose-Na+ symport
Which of the following statements about molecular switches is false? They exist in two states: an active state and an inactive state. They are common components of intracellular signaling pathways. One class of molecular switch are G proteins whose activity is in the ON state when bound to GDP. One class of molecular switch are proteins regulated by phosphorylation. G proteins are a type of molecular switch.
One class of molecular switch are G proteins whose activity is in the ON state when bound to GDP.
A nuclear localization signal (NLS) is a sorting signal that consists of ____________. A. A stretch of hydrophobic amino acids. B. One or two stretches of negatively charged amino acids. C. One or two stretches of positively charged amino acids. D. A sequence corresponding to KDEL (LysAspGluLeu).
One or two stretches of positively charged amino acids.
Which of the following statements about a G protein is false? Upon activation the alpha subunit dissociates from the beta gamma complex. Many G proteins can be activated when a signal binds a GPCR. Hydrolysis of the GTP on the alpha subunit results in inactivation of the G protein. Only the alpha subunit of an active G protein can activate membrane-bound ion channels and enzymes.
Only the alpha subunit of an active G protein can activate membrane-bound ion channels and enzymes.
Which of the following statements about protein import into the ER is false? Import into the ER is co-translational. Protein synthesis continues at a fast rate after the SRP binds to a newly exposed ER signal sequence. It requires protein translocators. Signal peptidases cleave off the ER signal sequence. Transmembrane proteins are only partially translocated across the ER membrane. Transmembrane proteins are only partially translocated across the ER membrane.
Protein synthesis continues at a fast rate after the SRP binds to a newly exposed ER signal sequence.
Which of the following statements about receptor tyrosine kinases (RTKs) is false? RTKs span the lipid bilayer seven times. RTKs have an intracellular kinase domain. Upon binding a signal, RTKs dimerize and undergo phosphorylation. Tyrosine phosphorylation of the receptor tails is important for signal transduction. RTKs regulate many cellular responses including cell growth and cell proliferation.
RTKs span the lipid bilayer seven times.
Which of the following statements about Ras is false? Ras is a monomeric GTPase. Ras-GEF activates Ras by promoting the exchange of GDP for GTP. Ras-GAP inactivates Ras by stimulating the hydrolysis of GTP. Ras resembles the gamma subunit of a heterotrimeric G protein. Mutations in Ras are associated with many human cancers.
Ras resembles the gamma subunit of a heterotrimeric G protein.
Which of the following statements regarding sorting signals is false? Sorting signals are often found at the N-termini of proteins. Different sorting signals direct proteins to different destinations. A nuclear localization signal (NLS) directs a protein to the nucleus. Sorting signals are usually between 15 and 60 amino acids long. Sorting signals are only rarely removed after the protein arrives at its final destination
Sorting signals are only rarely removed after the protein arrives at its final destination.
Which of the following statements is false? CO2 and O2 diffuse freely across cell membranes. The differences in permeability between artificial lipid bilayers and cell membranes arise from variations in phospholipid content. Transporters, but not channels, bind specifically to solute molecules. Cells expend energy in the form of ATP hydrolysis to maintain ion concentrations inside the cell that differ from those found outside the cell.
The differences in permeability between artificial lipid bilayers and cell membranes arise from variations in phospholipid content.
Which of the following statements about nuclear import is false? Nuclear pores are perforations in the nuclear envelope. Cytosolic proteins called nuclear import receptors bind to the nuclear localization signal on newly synthesized proteins destined for the nucleus. The nuclear import receptor delivers the protein destined for the nucleus to the nuclear pore but does not travel through the pore. The nuclear pore contains a mesh-like network in the center of the pore.
The nuclear import receptor delivers the protein destined for the nucleus to the nuclear pore but does not travel through the pore.
Which of the following statements about coat proteins is false? A. Different vesicles have different protein coats on their cytosolic surface. B. The protein coat of a vesicle remains on the vesicle until it fuses with its target membrane. C. Clathrin is a coat protein that forms a basket-like structure on the cytosolic surface of a vesicle. D. The coat protein helps in vesicle formation.
The protein coat of a vesicle remains on the vesicle until it fuses with its target membrane.
Which of the following statements about import into mitochondria is false? Proteins imported into mitochondria cross the outer and inner membranes together. Proteins must be unfolded for import into mitochondria. This type of import involves protein translocators. The sorting signal is not removed from proteins imported into mitochondria.
The sorting signal is not removed from proteins imported into mitochondria.
Which of the following statements about second messengers is false? They are products of an activated enzyme. They act by phosphorylating enzymes. They are small molecule generated inside the cell after a signal binds to a receptor. They are produced in large numbers.
They act by phosphorylating enzymes.
Which of the following is a characteristic feature of all transporters? They are peripheral membrane proteins. They exhibit specificity for a particular substance. They require the expenditure of cellular energy to function. They have few hydrophobic amino acids.
They exhibit specificity for a particular substance.
Which of the following statements is true? Transporters change shape when a specific molecule binds to them and use these conformational changes to move it across the membrane while channel proteins provide corridors for specific molecules to pass through. Channels transport substances at a slower rate compared with transporters. Transporters move molecules only via passive transport. Channels transport ions via passive or active transport.
Transporters change shape when a specific molecule binds to them and use these conformational changes to move it across the membrane while channel proteins provide corridors for specific molecules to pass through.
The growth factor Superchick stimulates the proliferation of cultured chicken cells. The receptor that binds Superchick is a receptor tyrosine kinase (RTK), and many chicken tumor cell lines have mutations in the gene that encodes this receptor. Which of the following types of mutation would be expected to promote uncontrolled cell proliferation? a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor a mutation that prevents dimerization of the receptor a mutation that prevents the binding of the normal extracellular signal to the receptor a mutation that destroys the kinase activity of the receptor
a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor
In which of the following steps does amplification occur? binding of an extracellular signal to a GPCR activation of G proteins by an activated GPCR activation of an enzyme by a G protein activation of protein kinase A (PKA) by cAMP
activation of G proteins by an activated GPCR
Which of the following events is not required for activation of Ras by a receptor tyrosine kinases (RTK)? binding of signal to a RTK phosphorylation of tyrosine residues on a RTK activation of phospholipase C binding of an adapter protein to phosphorylated tyrosine residues binding of Ras-GEF to an adapter
activation of phospholipase C
Pumps are transporters that are able to harness energy provided by other components in the cells to drive the movement of solutes across membranes, against their concentration gradient. This type of transport is called ___________. A. active transport B. simple diffusion C. facilitated diffusion D. passive transport
active transport
extracellular signal -> GPCR -> G protein -> __________ -> cAMP -> protein kinase A (PKA) -> transcription regulator -> change in gene expression Ca2+ adenylyl cyclase phospholipase C calmodulin MAP kinase
adenylyl cyclase
Ion channels _________ A. are not selective for a particular ion B. require an input of energy in order to function C. can transport both negative and positive ions through the same channel D. allow passage of ions in both directions
allow passage of ions in both directions
Type of transport that requires proteins to unfold. transport into the nucleus transport of proteins into the ER transport of proteins into the mitochondria both a and b both b and c
both b and c
Which of the following best describes the function of the signal recognition particle (SRP)? binds to the ribosome brings the ribosome to the SRP receptor stops translocation brings the growing protein to the protein translocator cleaves the N-terminal signal sequence
brings the ribosome to the SRP receptor
Which of the following second messengers is generated by an activated adenylyl cyclase? Ca2+ cAMP DAG IP3 none of the above
cAMP
Indirect signaling effects of Ca2+ are mediated by _______________. MAP kinase G proteins phospholipase C calmodulin
calmodulin
Which of the following types of signaling involves membrane-bound signal molecules?
contact-dependent
Cellular location of a protein that does not contain a signal sequence. A. golgi apparatus. B. plasma membrane C. ER D. cytoplasm E. mitochondria
cytoplasm
Which of the following types of cell signaling involves extracellular signals called hormones? endocrine paracrine contact-dependent neuronal/synaptic
endocrine
Protein kinase C is activated by _______________. interaction with Ca2+ and DAG covalent binding of cAMP phosphorylation by MAP kinase exchange of GDP for GTP
interaction with Ca2+ and DAG
Which of the following statements about protein glycosylation is false? N-linked glycosylation involves the addition of a preformed oligosaccharide to proteins in the ER. The preformed olgiosaccharide is transferred to an asparagine side chain of a protein. The preformed oligosaccharide is attached to the ER membrane via its association with a special lipid in the ER called dolichol. After attachment to the protein, the oligosaccharide is later modified to produce a diverse set of glycoproteins. none of the above
none of the above
All of the following are needed for import of proteins into the ER except: ER signal sequence protein translocators nuclear import receptor signal recognition particle (SRP) SRP receptor
nuclear import receptor
All of the following parts of a eukaryotic cell are connected through vesicular traffic except ER Golgi endosomes plasma membrane nucleus
nucleus
Proteins that are fully translated on ribosomes floating free in the cytosol do not end up in the __________. nucleus mitochondria cytosol chloroplast plasma membrane
plasma membrane
Some cells express aquaporin proteins; they are channel proteins that facilitate the flow of water molecules through the plasma membrane. What regulates the rate and direction of water diffusion across the membrane? A. aquaporin conformation B. resting membrane potential C. solute concentrations on either side of the membrane D. availability of ATP
solute concentrations on either side of the membrane
The hydrophobic amino acid sequence that halts the translocation of a transmembrane protein across the membrane is called a ______________.
stop transfer sequence
v-SNARE proteins on the vesicle surface are recognized by __________ proteins on the target membrane surface. v-SNARE t-SNARE tethering proteins dolichol dynamin
t-SNARE
The length of time a G protein is active is determined by _______. the activity of phosphatases that turn off G proteins by dephosphorylating the alpha subunit the activity of phosphatases that convert GTP into GDP the degradation of the G protein after the alpha subunit separates from the beta gamma complex the GTPase activity of the alpha subunit the GTPase activity of the beta gamma complex
the GTPase activity of the alpha subunit
During activation of a heterotrimeric G protein by a G protein-coupled receptor, ________. the alpha subunit exchanges GDP for GTP the beta subunit with GTP bound dissociates from the alpha gamma complex the alpha subunit phosphorylates its bound GDP to GTP the alpha subunit with GDP bound re-associates with the complex the alpha subunit hydrolyzes its bound GTP to GDP
the alpha subunit exchanges GDP for GTP
Which of the following proteins is a likely target of a signaling pathway that only results in a cellular response 24 hours after exposure of the cell to an extracellular signal molecule? K+ channel transcriptional regulator enzyme involved in respiration cytoskeletal protein enzyme involved in glycogen metabolism
transcriptional regulator
Which of the following describes a transporter known as an antiport?
two substances move in opposite directions across a membrane
Which of the following describes a transporter known as an antiport? two substances move in the same direction across a membrane two substances move in the same direction and one moves in the opposite direction across a membrane two substances move in opposite directions across a membrane movement of a single substance out of a cell
two substances move in opposite directions across a membrane
Which of the following describes a transporter known as an antiport? A. two substances move in the same direction across a membrane B. two substances move in the same direction and one moves in the opposite direction across a membrane C. two substances move in opposite directions across a membrane D. movement of a single substance out of a cell
two substances move in opposite directions across a membrane
Rabs and tethering proteins are important for: A. vesicle formation B. vesicle cargo selection C. vesicle docking D. vesicle fusion E. none of the above
vesicle docking
Function of the vesicle coat protein. A. cargo selection B. vesicle docking C. vesicle fusion D. vesicle formation E. none of the above
vesicle formation
