Exam 3 Biol 302 University of South Carolina spring 2023

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.

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.

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. A mutation in the alpha subunit of the G protein that prevents GTP hydrolysis.

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. All proteins exhibit functions after being transported to certain compartments of the cell.

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

Cargo receptors

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.

Channels can perform active transport.

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

Dynamin

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

Glycosylation starts in the ER and continues in the cytosol.

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

Hormone

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

Hydrophillic

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.

It performs active transport.

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

Lys-Asp-Glu-Leu (KDEL) at the C-terminus

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)

Lysine (K) and Arginine (R)

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.

Misfolded proteins in the ER activate the UPR by activating proteins in the ER lumen.

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

PKC (protein kinase C)

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

Rabs

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

Ras

The figure below shows the organization of a protein that normally resides in the plasma membrane. The boxes labeled 1 and 2 represent membrane-spanning sequences and the arrow represents a site of action of signal peptidase. Given this diagram, which of the following statements must be true? a. The N-terminus of this protein is cytoplasmic. b. The C-terminus of this protein is cytoplasmic. c. The mature version of this protein will span the membrane twice, with both the N- and C- terminus in the cytoplasm. d. None of the above.

The C-terminus of this protein is cytoplasmic.

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.

The Na+/K+ pump moves one Na+ out of the cell and one K+ into the cell.

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.

The glucose-Na+ symport pumps Na+ outside the cell while glucose goes down its concentration gradient.

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.

The protein would remain in the cytosol.

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.

The uphill transport of a solute is coupled to movement of ATP across a membrane.

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.

They are single pass transmembrane proteins.

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.

Transport of an ion across a membrane depends on only its concentration gradient.

. 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.

Upon activation, the beta subunit dissociates from the alpha/gamma complex.

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. Clathrin molecules are important for binding and selecting cargoes for transport.

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. Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior.

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. specific binding to solutes

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

activation of an enzyme by a G protein

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

antiport

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. Activated G proteins can activate cytosolic enzymes and ion channels.

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.

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. Oxygen, glucose, sodium ions

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. Protein kinases transfer the terminal phosphate from ATP to a protein.

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. a mutation that prevents RGFR from binding to RGF

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. mutant Ras protein unable to hydrolyze its bound GTP

3. 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. reception, transduction, activation of cellular response

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. receptor tyrosine kinases

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

binds to an ER signal sequence

8. 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

both c and d

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. 4, 1, 5, 3, 2

Which of the following is not a second messenger important in the inositol phospholipid pathway? a. IP3 b. DAG (diacylglycerol) c. cAMP d. Ca2+

cAMP

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

contact-dependent

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. 3, 5, 4, 6, 1, 2

Which of the following choices reflects the appropriate order of locations through which a secretory protein travels? a. lysosome à endosome à plasma membrane b. ER à lysosome à plasma membrane c. Golgi à lysosome à plasma membrane d. ER à Golgi à plasma membrane e. Golgi à ER à plasma membrane

d. ER à Golgi à plasma membrane

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

encoded in the amino acid sequence and sufficient for targeting a protein to its correct destination

Proteins required in the cytosol, like the enzymes of glycolysis, 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

free ribosomes in the cytosol

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

import receptor protein

The figure below shows the organization of a protein that resides on the ER membrane. The N- and C-termini of the protein are labeled. Boxes 1, 2, and 3 represent membrane-spanning sequences. Non-membrane-spanning regions of the protein are labeled "X," "Y," and "Z." Where will region Y be when translocation is completed? a. in the cytosol b. in the ER lumen c. inserted into the ER membrane d. degraded by signal peptidase

in the cytosol

Import into which of the following cell compartments does not require protein unfolding? a. chloroplasts b. ER c. nucleus d. mitochondria

nucleus

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

one of the membrane-bound organelles because it is being transported via a vesicle

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

paracrine

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

protein translocator

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

ribosomes on endoplasmic reticulum

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

short peptide sequences that serve as an address for transporting newly synthesized proteins to their correct cellular location

1. 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

via vesicular traffic