Weeks 1-5

Quiz 7: Taxol (Paclitaxel) is a natural compound derived from the Pacific Yew tree. It binds to microtubules and completely inhibits microtubule depolymerization. This compound is used as an anti-cancer drug because cells are unable to undergo cell division in its presence. Which of the following FRAP graphs best describes the effect of taxol on interphase cells?

A

Weekly Quiz 2: Leigh's Syndrome is a mitochondrial disease that affects the function of complexes of the respiratory chain and of ATP Synthase. Below are five genetic pedigrees. Which of this pedigree describes how a mutation in a gene encoded by mitochondrial DNA is passed on between generations? (Note: females are shown as circles, males as squares)

A

Quiz 13: Which of the following proteins/protein complexes is critical for the ubiquitination of a substrate? A: E3 ligase B: Proteosome C: De-ubiquitinase D: Kinase E: Phosphatase

A: E3 ligase

Quiz 4: In an in vitro polymerization reaction of F-actin from its G-actin subunits, there is a lag phase (rate-limiting stage). What happens during this lag phase? A: F-actin is nucleated B: F-actin reaches a steady state C: F-actin exchanges nucleotides D: F-actin hydrolyzes ATP E: F-actin undergoes treadmilling

A: F-actin is nucleated

Quiz 7: Which of the following describes a common feature of F-actin, microtubule, and intermediate filament? A: They are all made of up small subunits B: They all provide tracks for molecular motors C: Their assembly depends on ATP hydrolysis D: Their assembly depends on GTP hydrolysis E: They all have two same ends

A: They are all made of up small subunits

Quiz 4: What is GFP? A: a protein B: a secondary antibody C: a primary antibody D: a lipid E: a chemical

A: a protein

Quiz 1: Which of the following amino acids is least likely to be found in a transmembrane domain? A: Met B: Arg C: Ala D: Phe E: Leu

B: Arg

Quiz 6: What is the function of gamma-Tubulin? A: It is a critical component of the microtubule B: It nucleates microtubule at the centrosome C: It protects the (+) end from dynamic instability D: It binds alongside the microtubule E: It is a critical component of centriole

B: It nucleates microtubule at the centrosome

Quiz 7: Which microtubule (MT) population binds to chromosomes during mitosis? A: Astral MTs B: Kinetochore MTs C: Interpolar MTs D: Either MT population is able to bind chromosome because they are functionally redundant E: MT does not associate with chromosomes at all

B: Kinetochore MTs

Quiz 5: How would inhibition of Rac GEF protein affect cell migration? A: Cells would migrate normally B: Cells would migrate non-directionally C: Cells would not migrate D: Cells would not be able to detect the signal that induces migration E: Cells would be unable to undergo actin treadmilling

C: Cells would not migrate

Weekly Quiz 3: You are examining the behavior of two centrosome proteins Centrin and Cep192 by FRAP analysis inside cells. Both proteins are expressed as GFP-tagged forms and localize to the centrosome (the centrosome is indicated by the red arrow; the plasma membrane is indicated by the dashed line). The small images show a magnified version of these centrosomes (either 1 spot, or 2 spots), p.b. is before bleaching, the subsequent images show time points during recovery from photobleaching (time is indicated in minutes and the time course shows the fluorescent signal at the centrosome over time, always focusing on the centrosome). Which of the following conclusions can you draw from this experiment? A: Both, Centrin and Cep192 are stably associated with the centrosome and do not exchange with cytosolic subunits B: Centrin-GFP displays a more dynamic behavior than Cep192-GFP C: Cep192-GFP is more dynamic than Centrin-GFP D: The dynamic behavior of Cep192-GFP and Centrin-GFP is similar E: The dynamic behavior of these proteins depends on the cell cycle stage

C: Cep192-GFP is more dynamic than Centrin-GFP

Weekly Quiz 3: You are studying the mechanism of assembly and disassembly of the nuclear lamina (made up of lamin A and lamin C) in vitro (i.e., with purified proteins in a test tube). Based on your knowledge from the D103 Cell Bio class, which of the following amino acid changes would you make to prevent assembly of the nuclear lamina? (Please note that phosphorylation of a Ser residue in lamin A at the onset of mitosis leads to disassembly of the nuclear lamina) A: Change the Ser to a Thr B: Change the Ser to an Ala C: Change the Ser to an Asp D: Change the Ser to an Arg E: Change the Seri to a Gly

C: Change the Ser to an Asp

Quiz 2: Imagine a small synthetic vesicle made from pure phospholipids (formed as lipid bilayer). Its lumen contains 1 mM Glucose and 1 mM sodium chloride (NaCl). If the vesicle is placed in pure water, which of the following happens the fastest? A: Na+ diffused out B: Cl- diffused out C: H2O diffused in D: Glucose diffused out E: Nothing happens

C: H2O diffused in

Quiz 10: What is the most likely fate of a protein in which a mutation has led to its misfolding in the ER? A: It is sequestered by the proteasome in the cytosol B: It is first tagged with ubiquitin in the ER and then degraded by the proteasome in the cytosol C: It is first moved out of the ER, tagged with ubiquitin in the cytosol, and then degraded by the proteasome in the cytosol D: It associates with many chaperones in the ER, which guarantee its correct folding E: Its misfolded state is recognized by chaperones in the ER, which will induce the protein's degradation by the proteasome in the ER

C: It is first moved out of the ER, tagged with ubiquitin in the cytosol, and then degraded by the proteasome in the cytosol

Weekly Quiz 4: Which of the following statements best describes a shared characteristic of co-translational protein import into the ER and protein import into the mitochondrial matrix? A: Proteins to be imported are recognized by SRP B: Proteins to be imported are unfolded by a chaperone of the Hsp70 family C: Proteins to be imported into both organelles have to be in an unfolded conformation D: Protein import depends on the activation state of a small GTPase E: Protein import depends on an ATPase that pulls the protein across the membrane

C: Proteins to be imported into both organelles have to be in an unfolded conformation

Quiz 11: Which of the following statements best describes the COPI and COPII vesicles? A: They mediate all the vesicle transports in the cells B: They share some components for vesicle budding C: They both depend on small GTPases to initiate the vesicle formation D: They can deliver proteins to plasma membrane E: All their coat proteins will be degraded after being transported to target membrane

C: They both depend on small GTPases to initiate the vesicle formation

Quiz 5: Which of the following statement best describes an effector of a small GTPase? A: it is a protein that only binds to the small GTPase when that small GTPase is localized to the membrane B: it is a protein that only binds to the small GTPase in its GDP bound form C: it is a protein whose activity is regulated by a small GTPase GTP bound form D: it is a protein that mediates actin nucleation E: it is a protein that is drives GDP/GTP exchange for a small GTPase

C: it is a protein whose activity is regulated by a small GTPase GTP bound form

Quiz 7: You would like to determine the functional relationship between nuclear lamina disassembly and chromosome condensation, which both happen at the beginning of mitosis. Which of the following experiments would most help with your study? A: tag lamin A with GFP and monitor by live imaging B: mark the DNA fluorescently and monitor by live imaging (this can be done by expressing a fluorescent histone) C: prevent the disassembly of the nuclear lamina and monitor chromosome condensation D: perform immunofluorescence analysis with antibodies that detect the nuclear lamina and chromosomes E: prevent the assembly of the nuclear lamina and examine gene transcription

C: prevent the disassembly of the nuclear lamina and monitor chromosome condensation

Quiz 5: What is the most likely consequence of expressing a dominant negative form of the small GTPase Rac1 in a human neutrophil? (Note: dominant negative mutant displays inhibitory effect on the wildtype protein) A: the GEF for Rac will be inactivated B: the GAP for Rac will be inactivated C: the lamellipodia formation will be blocked D: the formation of linear stress fibers will be blocked E: the formation of branched actin fibers will be enhanced

C: the lamellipodia formation will be blocked

Quiz 12: Which of the following describes the most direct way for disrupting LDL-receptor-dependent delivery of cholesterol to the lysosome? A: to block the formation of ER-derived vesicles B: to block the formation of Golgi-derived vesicles C: to prevent acidification of the endosome D: to prevent the formation of the mannose 6-Phophate sorting signal E: to prevent the co-translational transport of proteins into the ER

C: to prevent acidification of the endosome

Quiz 2: You have identified a novel sodium channel: this protein forms a homo-tetramer, with each subunit containing 5 transmembrane domains. How many hydrophobic domains to you predict to see in a hydrophobicity plot of this sodium channel? A: 5 B: 10 C: 15 D: 20 E: Hydrophobicity plot cannot be generated for this protein

D: 20

Weekly Quiz 1: The nicotinic acetylcholine receptor is a cation channel in the plasma membrane of some neurons. It is composed of five subunits, each of which is a transmembrane protein. The hydropathy plot of one of the subunits is shown. How many membrane-spanning alpha helices do you predict for this protein subunit? (The plasma membrane of a neuron is 3.5 nm thick) A: 1 B: 2 C: 3 D: 4 E: 6 F: 8

D: 4

Quiz 2: Which of the following molecules is most likely to induce a conformational change in a uniporter that transports glucose across the plasma membrane? A: An extracellular ligand B: An intracellular ligand C: There is no need for a ligand, as the transporter changes conformation spontaneously D: A molecule of glucose E: A Na+ ion

D: A molecule of glucose

Quiz 1: Which factors are likely to lead to a decrease in membrane fluidity? A: An increase in the number of unsaturated bonds in the hydrophobic tail of phospholipids B: An increase in the activity of a transmembrane protein C: A change in the molar ratio of PC to PE D: An increase in the number of phospholipids with long hydrophobic tails

D: An increase in the number of phospholipids with long hydrophobic tails

Quiz 1: Why is cholesterol able to integrate into a lipid bilayer? A: Because it is a small molecule B: Because it is a fully hydrophobic molecule C: Because it is abundant D: Because it has an amphipathic organization, similar to membrane lipids E: Because it can bind covalently to phospholipids

D: Because it has an amphipathic organization, similar to membrane lipids

Quiz 6: Which statement best describes a feature that is shared between kinesin and dynein? A: Both proteins "walk" towards the (+) end of a microtubule B: Both proteins "walk" towards the (-) end of a microtubule C: Both proteins bind ATP and F-actin D: Both proteins function in the positioning of organelles inside of cell E: Both proteins associate with the same regulatory factors

D: Both proteins function in the positioning of organelles inside of cell

Weekly Quiz 3: Which of the following graphs best describes the behavior of GFP-Centrin and Cep192-GFP? A: Centrin: B, Cep192: C B: Centrin: A: Cep192: C C: Centrin: C: Cep192: B D: Centrin: C Cep192: A E: Centrin: A, Cep192: D

D: Centrin: C Cep192: A

Weekly Quiz 4: Changes in integrin function can lead to cancer cell metastasis because... A: Integrins are important for the formation of cell-cell contact B: Integrins bind to actin via specific actin binding proteins C: Integrins signal from the outside to the cytosol, but also from the cytosol to the outside of the cell D: Integrins mediate adhesion of cells to the basal membrane E: Integrins undergo a conformational change upon activation

D: Integrins mediate adhesion of cells to the basal membrane

Weekly Quiz 3: You are comparing microtubules (MTs) and intermediate filaments. Which of the statements below provides as correct description of the difference between these two cytoskeletal structures? A: Energy - intermediate filaments and MTs both need energy inputs to polymerize B: Accessory proteins - intermediate filaments don't associate with other proteins, while accessory MT binding proteins are critical regulators of MT dynamics C: Building block - in contrast to the alpha/beta tubulin heterodimer, the intermediate filament dimer is ATP bound during its assembly D: Motor protein - while MTs associate two different types of motor proteins, motor proteins that move along intermediate filaments are rarely known E: Role in cell cycle - MTs play critical roles in mitosis while intermediate filaments are not

D: Motor protein - while MTs associate two different types of motor proteins, motor proteins that move along intermediate filaments are rarely known

Quiz 1: Which of the following organisms is most likely to have the highest percentage of unsaturated fatty acid chains in their membranes? (hint: organisms try to preserve the balance for their membrane dynamics) A: Antarctic bacterium B: Desert iguana C: Human being D: Polar bear E: Thermophilic bacterium

A: Antarctic bacterium

Quiz 8: Which feature is shared between adherens junctions and desmosomes? A: Both needs Ca2+ to function B: Both connect the intermediate filaments of neighboring cells C: Both only contain cadherin and cytoskeleton D: Both promote cell migration E: Both have outside-in and inside-out signaling

A: Both needs Ca2+ to function

Quiz 9: Which of the following statements best describes the protein interactions during nuclear import? A: During nuclear import, a cargo protein interacts with the importin receptor via its NLS B: During nuclear import, a cargo protein interacts with Ran-GDP in the cytosol C: During nuclear import, a cargo protein interacts with Ran-GTP in the cytosol D: During nuclear import, a cargo protein interacts with Ran-GTP in the nucleus E: During nuclear import, a cargo protein interacts with the components of the nuclear pore F: During nuclear import, a cargo protein interacts with a protease that removes the NLS

A: During nuclear import, a cargo protein interacts with the importin receptor via its NLS

Quiz 4: You have performed an immunofluorescence experiment in which you have stained the Golgi (white) and microtubules (red). Which information does this image give you? (the nucleus is stained in blue with a DNA dye) A: Golgi membranes are localized next to the nucleus B: Golgi membranes depend on microtubule for their localization C: Microtubules are nucleated and anchored at the centrosome, the major microtubule organizing center of the cell D: Golgi membranes function in protein sorting E: Golgi membranes are dynamic during the cell cycle

A: Golgi membranes are localized next to the nucleus

Quiz 3: Which of the following statements best describes properties of mitochondrial DNA? A: It is circular B: It contains more nucleotides than nuclear DNA C: It encodes all proteins found in mitochondria D: It is transported into the cytosol for transcription and translation E: It is replicated in parallel with nuclear DNA

A: It is circular

Quiz 11: Which of the following statements best describes the role of a vesicle coat proteins? A: It recruits cargo protein to the site of vesicle budding B: It selects specific phospholipids for inclusion into the vesicles C: It mediates the fusion of the vesicle with the target membrane D: It induces the activation of the small GTPase E: It interacts with microtubules for efficient transport

A: It recruits cargo protein to the site of vesicle budding

Quiz 8: Which of the following factors is NOT a component of the extracellular matrix (ECM)? A: Keratin B: Collagen C: Fibronectin D: Fibroblasts E: Proteoglycans

A: Keratin

Quiz 13: Which of the following situations is a potential consequence of a phospho-mimetic mutation (mimic phosphorylation) in lamin A? A: Nuclear envelope does not assemble properly B: Protein import into the nucleus is blocked C: Protein export is blocked D: Cell division is blocked E: Transcription is blocked

A: Nuclear envelope does not assemble properly

Quiz 8: Which of the following experiments would allow you to test if an assembled keratin network exchanges subunits with keratin monomers in the cytosol? A: Perform a FRAP experiment in cells that express GFP-tagged keratin B: Perform immunofluorescence analysis using primary antibodies to keratin and the matching secondary antibody. C: Express a GFP-tagged keratin tetramer D: Express a keratin mutant that cannot assemble into a network E: Express GFP-tagged keratin and monitor this protein over time in a live imaging experiment

A: Perform a FRAP experiment in cells that express GFP-tagged keratin

Quiz 7: Which of the following signals induces the disassembly of the nuclear lamina, a structure assembled by lamin proteins? A: Phosphorylation by a mitotic kinase B: Activation of a small GTPase C: A conformational change of nuclear pore D: DNA condensation E: DNA replication

A: Phosphorylation by a mitotic kinase

Quiz 4: How would you test whether actin cytoskeleton promotes mitochondrial fission process? A: Prevent F-actin assembly and examine mitochondria dynamics by monitoring a GFP-tagged ATP synthase B: Prevent F-actin assembly and stain cells with an antibody to actin C: Stabilize F-actin and stain cell with an antibody to actin D: Increase F-actin treadmilling and monitor mitochondria organization by immunofluorescence with an ATP Synthase antibody E: Express an ATP-bound G-actin sequestering protein and visualize actin organization by immunofluorescence

A: Prevent F-actin assembly and examine mitochondria dynamics by monitoring a GFP-tagged ATP synthase

Quiz 1: Which information can you obtain from a hydrophobicity plot? A: The number of potential hydrophobic transmembrane domain B: The topology of the protein C: Where the protein localizes in the cell D: Its interaction partner E: The protein's function

A: The number of potential hydrophobic transmembrane domain

Quiz 1: Which of the following statement best describes how bacteria in a hot spring control the fluidity of their plasma membrane? A: They decrease the percentage of lipids with unsaturated fatty acid tails in their plasma membrane B: Because they don't synthesize cholesterol, they cannot control membrane fluidity and therefore have a very fluid plasma membrane. C: They reduce cholesterol production to prevent membranes from becoming too fluid. D: They form lipid rafts in their membranes to prevent too much fluidity E: They increase the percentage of lipids with unsaturated fatty acid tails in their plasma membrane

A: They decrease the percentage of lipids with unsaturated fatty acid tails in their plasma membrane

Quiz 12: The formation of the mannose 6 phosphate (M6P) sorting signal in the cis-Golgi is mediated by the enzyme N-acetylglucosamine phosphotransferase. How would an inhibitor of N-acetylglucosamine phosphotransferase affect lysosomal protein sorting? As a result of the treatment, lysosomal proteins ... A: are secreted to cell plasma membrane or outside of cells via the default secretory pathway B: are retained in the Golgi network C: are retained in the ER D: remain tightly bound to M6P receptors E: accumulate in the lysosome as non-functional precursor proteins

A: are secreted to cell plasma membrane or outside of cells via the default secretory pathway

Quiz 1: Which of these three 20 amino acid-long sequences is the most likely candidate for a transmembrane domain? (Different amino acids are highlighted) A: ile thr cys ile tyr phe gly val met ala gly val ile gly thr ile leu leu ile ser B: ile thr pro ile tyr phe gly tyr met ala gly val ile gly thr asn leu leu ile ser C: ile thr glu ile tyr phe gly arg met ala gly val ile gly thr glu leu leu ile ser

A: ile thr cys ile tyr phe gly val met ala gly val ile gly thr ile leu leu ile ser

Quiz 5: During skeleton muscle contraction, tropomodulin consistently binds to F-actin (-) end. What is the consequence of this tropomodulin binding? A: the F-actin (-) end is stabilized B: the depolymerization at the F-actin (+) end is blocked C: myosin binding to F-actin is blocked D: ATP hydrolysis by myosin is blocked E: Ca2+ can stimulate the contraction

A: the F-actin (-) end is stabilized

Quiz 1: How many transmembrane domains does this transmembrane protein have? A: none B: 4 C: 8 D: 1 E: 3

B: 4

Quiz 3: Immunofluorescence analysis of mitochondria in control and mutant cells gives you the following images. Mitochondria in wildtype cells are more linear than those in mutant cells. Which of the following proteins is most likely defective in this mutant? Mitochondrial protein TOM20 is labeled in red. A: ATP Synthase B: A mitochondrial fusion factor C: A mitochondrial fission factor D: A complex I component E: a TCA cycle enzyme

B: A mitochondrial fusion factor

Weekly Quiz 4: You have been invited to work as a Bio199 student in a developmental biology lab whose focus is early embryogenesis. All studies are performed in zebrafish, a powerful vertebrate model organism. You have identified a mutant fish that show early embryonic lethality. Under the microscope, the embryo looks disorganized, and the cells appear to adhere poorly to each other. Which protein do you hypothesize has lost its function because of this mutation? A: Integrin B: Cadherin C: Talin D: Alpha tubulin E: Collagen

B: Cadherin

Quiz 2: In contrast to transporters, channel proteins in cellular membrane: A: Undergo a conformational change every time they transport an ion solute B: Can only mediate passive transport C: Form pores that are always open D: Are always controlled by voltage

B: Can only mediate passive transport

Weekly Quiz 3: What do you expect to see if you fixed the cells from question 7 (after the FRAP experiment has been completed) and performed immunofluorescence microscopy staining, using specific primary antibodies to Centrin and Cep192, followed by staining with appropriate secondary antibodies? A: Centrin and Cep192 IF signals will be absent from the centrosome B: Centrin and Cep192 IF signals will both be present at the centrosome C: Cep192 IF signal, but not that of Centrin, will display a high level of motility at the centrosome D: Only Centrin IF signal will be absent from the centrosome, but Cep192 IF signal will still be present at the centrosome

B: Centrin and Cep192 IF signals will both be present at the centrosome

Quiz 9: Which of the following statements describes a typical feature of protein import into mitochondria? A: Proteins are imported in a fully folded state B: Protein import involves a chaperone that keeps the protein unfolded in the cytoplasm C: The entire process (from signal sequence recognition to signal peptide cleavage) does not require any energy D: Protein depends on diffusion of proteins through porins, followed by an active transport through a translocation channel E: All the mitochondria proteins require the protein import

B: Protein import involves a chaperone that keeps the protein unfolded in the cytoplasm

Quiz 13: Which of the following processes can be readily studied in the budding yeast Saccaromyces cerevisae? A: Heart development B: Protein transport C: Immune response D: Organ size control E: Cancer metastasis

B: Protein transport

Quiz 9: Which of the following statements best describes how the activity of the small GTPase Ran is regulated during nuclear import and export? A: Ran is activated by its GEF in the cytosol B: Ran is activated by its GEF in the nucleus C: Ran is activated by its GAP in the nucleus D: Ran is activated by its GAP in the nucleus E: Ran is inactivated by GDI, which extracts the small GTPase from the membrane

B: Ran is activated by its GEF in the nucleus

Weekly Quiz 2: Under which of the following conditions do you expect to see treadmilling of an actin filament? The critical concentrations of F-actin are: (+)end: 0.12 microM(-)end: 0.6 microM A: The cytosolic concentration of G-actin-ATP is 0.4 microM, but you have added 0.3 microM of the sequestering protein thymosin to your reaction. Thymosin binds to G-actin ATP at a ratio of 1:1 B: The cytosolic concentration of G-actin-ATP is 0.15 microM and of G-actin ADP is 0.6 microM C: The cytosolic concentration of G-actin-ATP is 0.7 microM, but your reaction also contains profilin, an enzyme that converts G-actin-ADP into G-actin-ATP D: The cytosolic concentration of G-actin-ATP is 0.4 microM, but you have added the (-)-end capping protein tropomodulin to your reaction E: The cytosolic concentration of G-actin-ATP is 0.1 microM

B: The cytosolic concentration of G-actin-ATP is 0.15 microM and of G-actin ADP is 0.6 microM

Weekly Quiz 1: Following up on the above question: Which of the following statements best describes how the mutations listed below would affect this protein? Ala in position 220 is mutated to Asp Met in position 221 to Glu Leu in position 222 to Lys Trp in position 223 to Pro Phe in position 224 to Arg Ile in position 225 to Ala Ser in position 226 to Thr (All these mutations are present in the mutant protein at the same time!) A: The mutant protein would not have any potential transmembrane domains B: The mutant protein would have 3 potential transmembrane domains C: The mutant protein would have 4 potential transmembrane domains D: The mutant protein would have 2 potential transmembrane domains E: The mutant protein would bind to each other to form a dimer

B: The mutant protein would have 3 potential transmembrane domains

Quiz 13: What is the most likely consequence of addition of the K48 polyubiquitin chain to a protein? A: it leads to the protein's export from the ER by retro-translocation B: it leads to degradation of the protein by the proteasome in the cytosol C: it leads to degradation of the protein by the lysosome D: it leads to a protein's stabilization in the cytosol E: it leads to recognition of the protein clathrin-coated vesicles

B: it leads to degradation of the protein by the proteasome in the cytosol

Quiz 4: Under which of the following conditions does F-actin grow at both ends? A: when Ccyto < Cc(-) and Cc(+) B: when Ccyto > Cc(-) and Cc(+) C: when there are a lot of ATP G-actin sequestering proteins in the reaction D: when Ccyto > Cc(-) but the (+) end is capped E: when Ccyto < Cc(+) but the (-) end is capped

B: when Ccyto > Cc(-) and Cc(+)

Quiz 4: Please indicate the identity of the cytoskeleton elements in the following cells? A: (1) actin; (2) microtubule; (3) intermediate filaments B: (1) microtubule; (2) actin; (3) intermediate filaments C: (1) microtubule; (2) intermediate filaments; (3) actin D: (1) intermediate filaments; (2) microtubule; (3) actin E: (1) intermediate filaments; (2) actin; (3) microtubule

C: (1) microtubule; (2) intermediate filaments; (3) actin

Weekly Quiz 1: You have identified a novel protein that associates with the plasma membrane. You do not know whether this protein is a peripheral or a transmembrane protein. You therefore analyze the primary amino acid sequence (listed in the three-letter code) for the presence of a transmembrane domain. Met - Asp - Leu - Lys - Ile - Pro - Gly - Val - Glu - Arg - Met - Phe - Leu - Ile - Ser - Lys - Gly - Thr - Asp - Tyr - His - Asn - Gln - Val - Asp - Met - Asp - Glu - Gly - Met - Arg - Trp - Lys - Cys - Met - Phe - Val - Thr - Val - Glu - Glu - Gly - Asp - Met - Val - Leu - Pro - Lys - Arg - Trp - Gly - Phe - Ala - Leu - Val - Ala - Val - Leu - Ile - Leu - Met - Ala - Trp - Leu - Val - Phe - Val - Ile - Leu - Ala - Arg - Lys - His - Ala - Val - Ile - Leu - Trp - Tyr - Ala - Gly - Gln - Gly - Asn - Arg - His - Cys - Lys - Met - Ser - Pro - Gly - Ala - Met - Asp - Ser - Glu - Ile - Leu - Met - Phe - Trp - Gly - Lys - Cys - Met - Leu - Trp - Phe - Arg - Met - Leu Can you predict which region can form a potential transmembrane domain in this protein? A: 1 B: 2 C: 3 D: 4 E: 5

C: 3

Weekly Quiz 1: Ca2+is a critical signaling molecule in muscle cells. Its cytosolic concentration is very low, but high concentrations of Ca2+ can be found in the sarcoplasmic reticulum where Ca2+ is stored. Which of the following statements is most correct to explain the FAST release of Ca2+ from the sarcoplasmic reticulum into the cytosol? A: A Ca2+ uniporter that takes advantage of the steep electrochemical gradient for Ca2+ is necessary for this regulated transport step B: An ATP-driven Ca2+ pump is necessary to transport Ca2+ from the sarcoplasmic reticulum into the cytosol C: A stimulus promotes the opening of a Ca2+ channel present in the membrane of the sarcoplasmic reticulum. D: Ca2+ moves across the membrane by diffusion, which is made possible by the steep electrochemical gradient across the membrane of the sarcoplasmic reticulum and the reduced thickness of the membrane of this ER-like organelle. E: A Ca2+ channel with a selectivity filter for Ca2+ is necessary in the plasma membrane

C: A stimulus promotes the opening of a Ca2+ channel present in the membrane of the sarcoplasmic reticulum.

Quiz 13: Which of the following provides a great example for regulation of a process by a posttranslational modification (PTM)? A: Microtubule assembly B: F-actin assembly C: ER-associated protein degradation (ERAD) D: Lamellipodium formation E: Skeletal muscle contraction

C: ER-associated protein degradation (ERAD)

Weekly Quiz 4: A mutation in a keratin protein in an epithelial cell leads to a highly fragile epithelial cell layer. Interestingly, this mutation does not appear to impact the overall organization of the cell. Which of the following processes do you predict to be blocked by this mutation? A: Binding of cadherin to cadherin of a neighbor cell B: Assembly of the nuclear lamina C: Formation of desmosome D: Formation of adherent junctions E: Assembly of keratin fibers

C: Formation of desmosome

Quiz 5: Which of the following answers describes the most direct consequence of tropomyosin binding to F-actin in a muscle cell? A: The (-) end of F-actin is stabilized B: Loss of actin-ADP subunits from the (+) end is prevented C: Myosin binding to F-actin is blocked D: ATP hydrolysis by myosin is blocked E: The movement of myosin towards the (+) end is blocked

C: Myosin binding to F-actin is blocked

Weekly Quiz 3: In melanocytes, pigment-containing granules are either dispersed throughout the cell or aggregated in the cell center, next to the centrosome. This specific localization depends on the regulated activity of the motor proteins kinesin and dynein. "Headless" kinesin mutants only contain the stalk (middle) and tail domains and can therefore dimerize with their wild-type kinesin partners. However, since they lack the motor (head) domain, the resulting dimers are unable to carry out processive transport of their cargoes and the mutation thus behaves as "dominant negative," meaning that the mutant not only is nonfunctional, but can also interfere with the function of its wild-type counterparts. If a headless mutant of a kinesin heavy chain involved in melanosome movement is overexpressed in fish melanocytes, what would you predict to happen in these cells? A: Pigment dispersion would be inhibited and there would be more tug-of-war between the motors B: Pigment aggregation would be inhibited and there would be more tug-of-war between the motors C: Pigment dispersion would be inhibited and there would be less tug-of-war between the motors D: Pigment aggregation would be inhibited and there would be less tug-of-war between the motors E: It is hard to conclude based on the information provided

C: Pigment dispersion would be inhibited and there would be less tug-of-war between the motors

Quiz 4: GFP tagging is a commonly used method to label cells for visualization by fluorescence microscopy. Which of the following statement is most correct? A: The GFP tag can only be placed on the N-terminus of a protein B: The GFP tag can attach to the phospholipids of any membrane C: The GFP tag allows for visualizing the dynamic behavior of a protein in a living cell D: The GFP tag disrupts the function of the protein to which it is attached E: The GFP tag can be visualized only in fixed cells

C: The GFP tag allows for visualizing the dynamic behavior of a protein in a living cell

Weekly Quiz 1: Which of the following statements is NOT correct? (Tip: A drawing may help you!) A: A eukaryotic cell is surrounded by a lipid bilayer B: A prokaryotic cell is surrounded by a lipid bilayer C: The two leaflets of the lipid bilayer of a eukaryotic cell always face the cytosol D: The matrix of the mitochondrion is surrounded by two lipid bilayer membrane E: The outer leaflet of the lipid bilayer surrounding the ER and the inner leaflet of the plasma membrane both face the cytosol

C: The two leaflets of the lipid bilayer of a eukaryotic cell always face the cytosol

Quiz 9: What does it mean that a sorting signal is necessary for the transport of a protein to a new location? A: Without the sorting signal, the protein will be degraded B: Without the sorting signal, the protein will be transported to the ER C: Without the sorting signal, the protein will remain in the cytosol D: Without the sorting signal, the protein cannot function E: Without the sorting signal in one protein, other proteins will not be transported to their destination

C: Without the sorting signal, the protein will remain in the cytosol

Quiz 8: The following schematic drawing shows two integrin molecules. Which one (a or b) is under the active configuration? Which side of the plasma membrane (1 or 2) represents cytoplasm? A: a; 1 B: a; 2 C: b; 1 D: b; 2

C: b; 1

Quiz 9: As a result of a mutation that disrupts the nuclear localization signal of a protein, the protein will now ... A: be translocated into the ER B: be ubiquitinated and degraded C: be remained in the cytoplasm D: be exported into extracellular matrix (ECM) E: be stuck in the nuclear pore

C: be remained in the cytoplasm

Quiz 3: Which of the following statements is most correct? (mito: mitochondria) The electron transport chain - A: generates a pH gradient that reduces O2 to H2O B: generates a proton gradient across the outer mito membrane C: generates a proton gradient across the inner mito membrane D: uses the energy stored in high energy electron carriers to synthesize ATP E: establishes a membrane potential across the outer mito membrane

C: generates a proton gradient across the inner mito membrane

Quiz 3: Which of the following pedigrees describes a mitochondrial mutation?

D

Quiz 12: Which of the following structures is not an organelle of the secretory pathway? A: ER B: Golgi C: Endosome D: Centrosome E: Lysosome

D: Centrosome

Quiz 12: Which of the following pathways describes the trafficking route through which a lysosomal enzyme would reach the lysosome to function there? A: ER --> Golgi --> cell surface --> lysosome B: Cell surface --> Golgi --> endosome --> lysosome C: Golgi --> ER --> Golgi --> lysosome D: ER --> Golgi --> endosome --> lysosome E: Cell surface --> endosome --> lysosome

D: ER --> Golgi --> endosome --> lysosome

Weekly Quiz 3: Which of the following conditions would specifically prevent a cell from forming the lamellipodia at its leading edge? A: Inhibition of a cell surface receptor that "sees" the migration inducing signal B: Inhibition of formin, a protein inducing linearized F-actin polymerization C: Overexpression of a G-actin ATP sequestering protein D: Expression of a dominant negative form of the small GTPase Rac E: Disrupting the function of Rho-GEF

D: Expression of a dominant negative form of the small GTPase Rac

Weekly Quiz 4: Which of the following statements describes the most suitable technique to test if the keratin 18 network inside the cell (see immunofluorescence image below) is dynamic? A: Western blot analysis to see if keratin 18 is phosphorylated B: Immunofluorescence analysis with primary antibodies to keratin 18 and appropriate fluorophore-tagged secondary antibodies C: Express RFP-tagged keratin 18 and perform immunofluorescence assay to visualize keratin 18 in cells D: FRAP experiment in cells that express RFP-tagged keratin 18 E: Micro-injection of untagged keratin 18 monomers

D: FRAP experiment in cells that express RFP-tagged keratin 18

Quiz 8: In the lab, we commonly grow eukaryotic cell lines on plastic dishes that are coated with fibronectin. Why does this fibronectin coat help with the growth of cells? A: Fibronectin makes the surface softer for the cells B: Fibronectin can directly interact with F-actin to support cell attachment to the dish C: Fibronectin provides structural support for the cells D: Fibronectin can directly bind cell surface receptors (integrins) for better cell adhesion to the dish E: Fibronectin is a critical component of the extracellular matrix

D: Fibronectin can directly bind cell surface receptors (integrins) for better cell adhesion to the dish

Weekly Quiz 3: You have learned that GDI is an important regulator of small GTPases, but its function in cell migration is not clear. A wound healing assay shows that expression of high GDI levels prevents cell migration. To assess actin organization in these cells, you perform immunofluorescence microscopy analysis with primary antibodies to actin and an appropriate secondary antibody. This experiment shows that actin organization at the leading edge of the cell is normal, but that there are fewer stress fibers in the cell body and the rear of the cell. Which of following answers is most consistent with your observation? A: GDI overexpression reduces the cytosolic concentration of G-actin ATP so that F-actin is rapidly depolymerized B: GDI overexpression stimulates the activity of Rho, which then binds to the actin nucleator formin to nucleate linear actin filaments C: GDI prevents a chemoattractant in the medium to bind to the receptor so that migration cannot occur D: GDI sequesters the small GTPase Rho in the cytosol so that it cannot be activated by its GEF E: GDI blocks the activation of Rac at the leading edge of the cell

D: GDI sequesters the small GTPase Rho in the cytosol so that it cannot be activated by its GEF

Weekly Quiz 1: After release into the synaptic cleft, the neurotransmitter dopamine is actively taken up by the cells via specific dopamine transporters. The drug cocaine interferes with this process and is therefore called a reuptake inhibitor. The inhibition of the transporter at a certain cocaine concentration is qualitatively represented in the following graph. Based on this graph, which of the following describes the effect of cocaine on the kinetics of dopamine reuptake by the transporter? A: In the presence of cocaine, the maximal rate of transport (Vmax) is reduced, but the apparent affinity of the transporter for dopamine is unaffected B: In the presence of cocaine, the maximal rate of transport (Vmax) is enhanced, but the apparent affinity of the transporter for dopamine is unaffected C: In the presence of cocaine, both the maximal rate of transport (Vmax) and the apparent affinity of the transporter for dopamine are both increased D: In the presence of cocaine, the maximal rate of transport (Vmax) is unaffected, but the apparent affinity of the transporter for dopamine is reduced E: In the presence of cocaine, both the maximal rate of transport (Vmax) and the apparent affinity of the transporter for dopamine are unaffected, but the transporter is nevertheless inhibited

D: In the presence of cocaine, the maximal rate of transport (Vmax) is unaffected, but the apparent affinity of the transporter for dopamine is reduced

Quiz 11: What is the most likely fate of a v-SNARE after the fusion of a vesicle with the target membrane? A: It is recycled back to the donor membrane in a complex with the t-SNARE B: It is transported to the cell surface in a complex with the t-SNARE C: It is degraded after ubiquitin-mediated targeting to the proteasome D: It is recycled back to the donor membrane after separation from the t-SNARE via an ATPase E: It is involved in the vesicle transport that originates from the target membrane

D: It is recycled back to the donor membrane after separation from the t-SNARE via an ATPase

Quiz 6: Which of the following statements best describes the GTP cap in the microtubule? A: A microtubule binding protein that caps the (+) end of a microtubule B: A microtubule binding protein that caps the (-) end of a microtubule C: It promotes microtubule shrinkage at the (+) end D: It is required for microtubule (+) end growth E: It stabilizes the microtubule (-) end

D: It is required for microtubule (+) end growth

Weekly Quiz 2: Through a genome wide screen, you have identified a protein that appears to be involved in ATP production. Because you love cell biology so much, you name your protein D103. You hypothesize that D103 localizes to mitochondria and hope to test it via experiments. Which of the following experiments would be most suitable to test your hypothesis? A: Tag D103 with GFP and observe its movement using time-lapse fluorescent microscope B: Perform immunofluorescence microscopy analysis in which you detect D103 with an antibody raised in rabbit (secondary antibody: goat- anti-rabbit green fluorophore) C: Perform a co-staining immunofluorescence microscopy analysis in which you detect D103 with an antibody raised in rabbit (secondary antibody: goat- anti-rabbit green fluorophore), and ATP synthase with an antibody raised in rabbit (secondary antibody: goat-anti-rabbit-red fluorophore). D: Perform a co-staining immunofluorescence microscopy analysis in which you detect D103 with an antibody raised in rabbit (secondary antibody: goat- anti-rabbit green fluorophore), and ATP synthase with an antibody raised in mouse (secondary antibody: goat-anti-mouse-red fluorophore). E: Perform a co-staining immunofluorescence microscopy analysis in which you detect D103 with an antibody raised in rabbit (secondary antibody: goat- anti-rabbit green fluorophore), and ATP synthase with an antibody raised in mouse (secondary antibody: goat-anti-mouse-green fluorophore).

D: Perform a co-staining immunofluorescence microscopy analysis in which you detect D103 with an antibody raised in rabbit (secondary antibody: goat- anti-rabbit green fluorophore), and ATP synthase with an antibody raised in mouse (secondary antibody: goat-anti-mouse-red fluorophore).

Quiz 10: Which of the following cytosolic factors is most likely to associate with the signal sequence of a protein that is targeted co-translationally to the ER? A: A chaperone of the HSP70 family B: The translocation channel C: The ribosome D: Signal recognition particle (SRP) E: Signal peptidase

D: Signal recognition particle (SRP)

Weekly Quiz 4: A screen has identified a mutant cell that is unable to migrate. Sequence analysis reveals the presence of two mutations in the integrin transmembrane domain. The mutations are as follows: Leu --> Asp and Trp --> Lys. Which of the following statements best describes a reason for why the mutant cell does not migrate in a fibronectin-coated dish? A: The cell cannot form desmosomes B: The cell cannot form stress fiber C: The cell cannot form the branched actin cytoskeleton at the leading edge D: The cell cannot adhere to the fibronectin that has been used to coat the dish E: The cell is unable to link its actin to the ECM

D: The cell cannot adhere to the fibronectin that has been used to coat the dish

Quiz 10: What is the most likely fate of a protein with an N-terminal hydrophobic sorting signal and an additional internal hydrophobic domain of 22 amino acids? A: The protein stays in the cytosol B: The protein is transported to mitochondria C: Because the protein has an N-terminal sorting signal, the protein is translocated all the way into the ER lumen D: The hydrophobic domain is recognized as a transmembrane domain once it is in the translocation channel and released sideways into the ER membrane E: The internal hydrophobic domain is cleaved off by signal peptidase

D: The hydrophobic domain is recognized as a transmembrane domain once it is in the translocation channel and released sideways into the ER membrane

Weekly Quiz 4: It was discussed in class that sailors in the last century often suffered from scurvy. Which of the following statements provides the best explanation for why vitamin C would have helped these individuals? A: Vitamin C promotes the synthesis of the fibronectin homodimer B: Vitamin c promotes the formation of the collagen triple helix by changing the collagen amino acid sequence C: Vitamin C promotes collagen secretion by inducing its cleavage D: Vitamin C promotes proline and lysine hydroxylation, which is necessary for collagen fibril assembly E: Vitamins C induces the formation of collagen homo-trimers

D: Vitamin C promotes proline and lysine hydroxylation, which is necessary for collagen fibril assembly

Quiz 7: What is a typical feature of an intermediate filament monomer? A: it contains an ATP binding site B: it contains a GTP binding site C: it has a transmembrane domain D: it can spontaneously polymerize E: it has many known protein regulators

D: it can spontaneously polymerize

Quiz 3: What is the role of cardiolipin in the inner mitochondrial membrane? A: it increases the fluidity of the membrane B: it induces membrane curvature to form the cristae C: it transports electrons across the membrane D: it limits the permeability of the membrane E: it activates porins

D: it limits the permeability of the membrane

Quiz 13: Which of the following describes a posttranslational modification? A: NLS binding to an import receptor B: GTP hydrolysis on the small GTPase Sar1, which controls the formation of COPII-coated vesicles C: binding of a small GTPase with an effector D: lamin A phosphorylation E: Glucose-induced conformational change in the GLUT1 transporter

D: lamin A phosphorylation

Quiz 2: Which of the following transporters that moves the two solutes in the direction indicated by the arrow is most likely to be a ATP-driven pump? The concentration of both solutes (red and blue) is higher outside of the cell.

E

Quiz 3: Which of the following statements best describes a factor(s) that is required for efficient ATP synthesis by mitochondria? (mito: mitochondria) A: An ATP-driven proton pump in the inner mito membrane. B: An electron gradient across the inner mito membrane. C: The Na+/K+ pump, which establishes an electrochemical gradient for Na+, that then drives proton movement. D: A proton gradient and membrane potential across the outer mito membrane. E: A steep electrochemical gradient for protons, made up of a pH gradient and a membrane potential across the inner mito membrane

E: A steep electrochemical gradient for protons, made up of a pH gradient and a membrane potential across the inner mito membrane

Quiz 8: In which of the following molecules does Ca2+induce a conformational change? A: Keratin B: Lamin C: Integrin D: Collagen E: Cadherin

E: Cadherin

Quiz 12: The dissociation of a mannose-6-phophate-containing (M6P) cargo protein from its receptor is regulated by which of the following factors? A: GTP hydrolysis B: ATP hydrolysis C: GDP for GTP exchange on the small GTPase Sar1 D: Protein degradation E: Change in the pH

E: Change in the pH

Quiz 11: What would be the most direct consequence of a mutation in Sar1 that prevents its recruitment to the ER membrane? (Note: Sar1 is the small GTPase that is required for the formation of COPII-coated vesicles; TM = transmembrane) A: A protein with a TM domain will not be released laterally into the membrane by the translocon B: Sar1-GEF is mis-localized from the ER membrane C: Cargo with one or several TM domains will not be sorted into the forming vesicle D: Soluble cargo will not be sorted into the forming vesicle E: Coat proteins will not be recruited to the ER membrane

E: Coat proteins will not be recruited to the ER membrane

Quiz 5: How would you determine if protein X is required for cell migration? A: Express the GAP of a small GTPase and measure cell migration B: Express the GEF of a small GTPase and measure cell migration C: Overexpress protein X and measure small GTPase activity D: Disrupt protein X and measure small GTPase activity E: Disrupt protein X and measure cell migration

E: Disrupt protein X and measure cell migration

Quiz 11: Which of the following transport route does an integrin take to reach the plasma membrane (PM), where it functions in linking the cell to the extracellular matrix? A: ER --> lysosome --> PM B: cytosol --> Golgi --> PM C: ER --> PM D: cytosol --> PM E: ER --> Golgi --> PM

E: ER --> Golgi --> PM

Quiz 4: Which of the following statements describes a correct fact about cytoskeletons (microtubules, F-actin and intermediate filaments)? A: All the three major cytoskeletons are non-hollow structure B: Intermediate filaments are typically thinner than actin filaments but thicker than microtubules. C: All three cytoskeletons share similar cellular localization D: All three cytoskeletal filaments provide support for the nucleus E: Each of the filaments is formed through the non-covalent assembly of their respective subunits.

E: Each of the filaments is formed through the non-covalent assembly of their respective subunits.

Weekly Quiz 2: Which of the following reagents would you use to achieve the following staining? Green shows mitochondria; red shows the microtubule cytoskeleton; blue shows the nucleus. (Note: DNA was detected with the DNA dye DAPI and does not have to be listed in your description. GFP, green fluorescent protein; RFP, red fluorescent protein) A: Use a primary antibody to a-tubulin (generated in mouse) and a secondary antibody (Goat anti-mouse) with a red fluorochrome; co-stain the same cells with a primary antibody to an ATP Synthase subunit (generated in rabbit) and a secondary antibody (Goat anti-rabbit) with a red fluorochrome B: Use a primary antibody to a-tubulin (generated in mouse) and a secondary antibody (Goat anti-mouse) with a red fluorochrome; co-stain the same cells with a primary antibody to an ATP Synthase subunit (generated in mouse) and a secondary antibody (Goat anti-mouse) with a green fluorochrome C: Express a GFP-tagged a-tubulin and an RFP-tagged form of an ATP synthase subunit in a cell D: Express a GFP-tagged a-tubulin in a cell and co-stain the cell with a primary antibody to an ATP Synthase subunit (generated in rabbit) and a secondary antibody (Goat anti-Rabbit) with a green fluorochrome E: Express an RFP-tagged a-tubulin in a cell and co-stain the cell with a primary antibody to an ATP Synthase subunit (generated in rabbit) and a secondary antibody (Goat anti-Rabbit) with a green fluorochrome

E: Express an RFP-tagged a-tubulin in a cell and co-stain the cell with a primary antibody to an ATP Synthase subunit (generated in rabbit) and a secondary antibody (Goat anti-Rabbit) with a green fluorochrome

Weekly Quiz 2: You would like to test if F-actin is required for the organization of ER. Which of the following experiments would most likely provide you with an answer to your question? A: Disrupt ER organization and examine the polymerization state of F-actin by immunofluorescence microscopy with suitable antibodies. B: Inhibit ER function and examine ER organization by immunofluorescence microscopy with suitable antibodies. C: Induce F-actin depolymerization and check for actin organization by immunofluorescence microscopy with suitable antibodies D: Use myosin inhibitor to inhibit F-actin tension and examine the dynamics of GFP-tagged actin subunit E: Induce F-actin depolymerization and examine ER organization by immunofluorescence with suitable antibodies

E: Induce F-actin depolymerization and examine ER organization by immunofluorescence with suitable antibodies

Quiz 9: What is the role of a sorting receptor? A: It binds to the signal sequence of a protein and targets the protein for degradation B: It cleaves off the signal sequence C: It binds the signal sequence only in the presence of ATP D: It recognizes a hydrophobic patch within the protein E: It binds to the signal sequence of a protein and targets the protein to a machinery that moves the protein into a new location

E: It binds to the signal sequence of a protein and targets the protein to a machinery that moves the protein into a new location

Quiz 6: Which of the following statements is a correct description of microtubule? A: Microtubule is composed of only alpha-Tubulin B: During polymerization, GTP on both alpha and beta Tubulin is hydrolyzed C: Microtubule depolymerization needs energy D: Microtubule can reach treadmilling E: Microtubule in cells is mostly depolymerized from one end but not the other

E: Microtubule in cells is mostly depolymerized from one end but not the other

Quiz 13: Which of the following size relationships is most correct? A: The membrane thickness: vesicle> E. Coli > mitochondria B: Yeast cell size > E.Coli size > epithelial cell size C: Oocyte size > E.Coli size > yeast cell size D: Oocyte size > sperm (head) size > epithelial cell size E: Mitochondrion size > vesicle size > membrane thickness

E: Mitochondrion size > vesicle size > membrane thickness

Quiz 13: Which of the following post-translational modifications is irreversible? A: Glycosylation B: Phosphorylation C: Methylation D: Poly-ubiquitination E: None of the above

E: None of the above

Quiz 12: Cell growth is commonly regulated by signaling receptors, whose levels at the cell surface are tightly controlled. Receptor reduction on the cell surface occurs by clathrin-mediated endocytosis and degradation in the lysosome, leading to decreased cell growth. What would be the consequences of a mutation in the AP2 adaptor, which is necessary for clathrin-mediated endocytosis? A: Receptor is taken up but cannot be degraded B: Receptor is endocytosed and degraded by alternative pathways C: Receptor is transported to the TGN D: Receptor is blocked in the ER during its intracellular transport E: Receptor remains at the cell surface leading to enhanced cell growth

E: Receptor remains at the cell surface leading to enhanced cell growth

Quiz 10: Which of the following statements best describes N-glycosylation? A: The addition of a pre-formed sugar tree to a serine or threonine present in the cytosolic domain of a protein B: The addition of a pre-formed sugar tree to a phospholipid to make a glycolipid C: The addition of individual sugar to selected amino acids in a protein D: The addition of a pre-formed sugar tree to an asparagine residue found within the consensus sequence Asn-X-Ser/Thr in the cytosolic domain of a protein E: The addition of a pre-formed sugar tree to an asparagine residue found within the consensus sequence Asn-X-Ser/Thr in an ER lumenal domain of a protein

E: The addition of a pre-formed sugar tree to an asparagine residue found within the consensus sequence Asn-X-Ser/Thr in an ER lumenal domain of a protein

Weekly Quiz 1: Which of the following processes will most likely occur when you transfer a bacterial culture from 37 degree C to 10 degree C? A: The bacteria will start synthesizing cholesterol B: The bacteria will remove cholesterol from their membranes C: The bacteria will reduce the number of unsaturated bonds in the fatty acid tails of their phospholipids D: The bacteria will increase the synthesis of phospholipids with very long fatty acid tails and insert these into their membranes E: The bacteria will increase the synthesis of phospholipids with unsaturated fatty acid tails and insert these into their membranes

E: The bacteria will increase the synthesis of phospholipids with unsaturated fatty acid tails and insert these into their membranes

Weekly Quiz 4: In the protein from question 3, Arg in position 8 is mutated to Asp, Lys in position 6 is mutated to a Leu, and Lys in position 9 is mutated to His. Which of the following statements best describes the most direct consequence produced by this mutation? A: The nucleus will be misshaped because many proteins, including lamin A, are no longer imported into the nucleus B: This mutation leads to a general disruption of nuclear import, which ultimately leads to the absence of many transcription factors from the nucleus and an overall defect in gene expression C: The mutated protein will remain in the cytosol, where it will now regulate gene expression D: Ran-GTP will remain in the cytosol because it cannot be converted into the GDP bound state E: The cells may transform to be cancerous because the tumor suppressor genes controlled by this protein will not be transcribed

E: The cells may transform to be cancerous because the tumor suppressor genes controlled by this protein will not be transcribed

Quiz 1: With which amino acid would you replace a Val in a transmembrane domain to maintain the hydrophobic character of this domain? A: Asp B: Lys C: Arg D: Glu E: Ala

E: Ala

Weekly Quiz 4: Studies from your lab have shown that a novel nuclear protein controls the transcription of several critical tumor suppressor genes. This protein was found to be downregulated in breast cancer cells. Careful sequence analysis reveals the following sequence in the N-terminus of this protein (the positions of the amino acids are indicated): Pro(1)-Pro(2)-Val (3)-Ala(4)-Arg(5)-Lys(6)-Lys(7)-Arg(8)-Lys(9)-Lys(10)-Lys(11)-Tyr(12)-Ile(13). A construct in which amino acids 1-10 are deleted does not localize to the nucleus. However, when you fuse amino acids 1-10 to GFP, GFP remains in the cytosol. Which of the following statements best describes the conclusion that you would draw from this experiment? A: Amino acids 1-10 are necessary and sufficient to target the protein into the nucleus B: The protein is imported into the nucleus C: Amino acids 1-10 are sufficient for the nuclear import of this protein D: Amino acids 1-10 are necessary for nuclear import because they interact with the Ran GTPase E: Amino acids 1-10 are necessary for nuclear import

E: Amino acids 1-10 are necessary for nuclear import

Quiz 2: What is the most likely consequence of a mutation in the acetylcholine binding site of an acetylcholine-gated Na+ channel in the post-synaptic nerve terminal? (Note: This mutation prevents the binding of acetylcholine to the channel) A: There is no effect B: The channel will not insert properly into the membrane C: The channel will now transport K+ D: The channel will stay in an open conformation E: The channel will not open when acetylcholine is present

E: The channel will not open when acetylcholine is present

Weekly Quiz 1: Which part of the Na+/Glucose symporter in the apical surface of an epithelial cell would you mutate so that it cannot transport glucose into the cell without affecting Na+ transport? A: The glucose binding site B: The Na+-binding site C: All the transmembrane domains D: The ATP-binding site E: There is no way the specificity of this transporter can be changed

E: There is no way the specificity of this transporter can be changed

Quiz 5: Which of the following statement best describes the role of Ca2+ during muscle contraction? A: it induces a conformational change in F-actin B: in induces a conformational change in myosin C: it induces a conformational change in the capping protein D: it activates myosin ATP hydrolysis E: it induces the binding of myosin to F-actin

E: it induces the binding of myosin to F-actin

Quiz 10: What is the overall goal of the unfolded protein response? A: to phosphorylate ER proteins B: to cleave ER proteins C: to decrease the protein modifications in the ER D: to increase the flux of proteins into the ER E: to increase the folding capabilities of the ER

E: to increase the folding capabilities of the ER