Unit 3
15-31 Figure Q15-31 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."
A
`15-34 Figure Q15-34 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?
B
Figure Q16-61 shows that intracellular signaling pathways can be highly interconnected.From the information in Figure Q16-61, which of the following statements is incorrect?(a) The GPCR and the RTK both activate phospholipase C.(b) Activation of either the GPCR or the RTK will lead to activation of transcriptional regulators.(c) CaM-kinase is only activated when the GPCR is active and not when the RTK is active.(d) Ras is activated only when the RTK is active and not when the GPCR is active.
CaM-kinase is only activated when the GPCR is active and not when the RTK is active
5-36 Which of the following choices reflects the appropriate order of locations through which a protein destined for the plasma membrane travels?(a) lysosome í endosome í plasma membrane(b) ER í lysosome í plasma membrane(c) Golgi í lysosome í plasma membrane(d) ER í Golgi í plasma membrane
ER--> golgi-->plasma membrane
You engineer yeast cells that express the M cyclin during S phase by replacing the promoter sequence of the M cyclin gene with that of S cyclin. Keeping in mind that yeast cells have one common Cdk that binds to all cyclins, which of the following outcomes is least likely during this experiment?(a) There will be both M cyclin-Cdk and S cyclin-Cdk complexes in the cell during S phase.(b) Some substrates that are normally phosphorylated in M phase will now be phosphorylated in S phase.(c) G1 cyclins will be expressed during S phase.(d) S-Cdk targets will be phosphorylated during S phase.
G1 cyclins will be expressed during S-phase
Which organelle fragments during mitosis?(a) endoplasmic reticulum(b) Golgi apparatus(c) mitochondrion(d) chloroplast
Golgi
You are interested in Fuzzy, a soluble protein that functions within the ER lumen. Given that information, which of the following statements must be true?(a) Fuzzy has a C-terminal signal sequence that binds to SRP.(b) Only one ribosome can be bound to the mRNA encoding Fuzzy during translation.(c) Fuzzy must contain a hydrophobic stop-transfer sequence.(d) Once the signal sequence from Fuzzy has been cleaved, the signal peptide will be ejected into the ER membrane and degraded.
Once the signal sequence from Fuzzy has been cleaved, the signal peptide will be ejected into the ER membrane and degraded.
Which of the following statements is true?(a) MAP kinase is important for phosphorylating MAP kinase kinase.(b) PI 3-kinase phosphorylates a lipid in the plasma membrane.(c) Ras becomes activated when an RTK phosphorylates its bound GDP to create GTP.(d) STAT proteins phosphorylate JAK proteins, which then enter the nucleus and activate gene transcription.
PI 3-kinase phosphorylates a lipid in the plasma membrane
The lab you work in has discovered a previously unidentified extracellular signal molecule called QGF, a 75,000-dalton protein. You add purified QGF to different types of cells to determine its effect on these cells. When you add QGF to heart muscle cells, you observe an increase in cell contraction. When you add it to fibroblasts, they undergo cell division. When you add it to nerve cells, they die. When you add it to glial cells, you do not see any effect on cell division or survival. Given these observations, which of the following statements is most likely to be true?(a) Because it acts on so many diverse cell types, QGF probably diffuses across the plasma membrane into the cytoplasm of these cells.(b) Glial cells do not have a receptor for QGF.(c) QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed.(d) Heart muscle cells, fibroblasts, and nerve cells must all have the same receptor for QGF. C
QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed.
Which of the following events does not usually occur during interphase?(a) Cells grow in size.(b) The nuclear envelope breaks down.(c) DNA is replicated.(d) The centrosomes are duplicated.
The nuclear envelope breaks down
Adrenaline stimulates glycogen breakdown in skeletal muscle cells by ultimately activating glycogen phosphorylase, the enzyme that breaks down glycogen, as depicted in Figure Q16-36.Which of the following statements is false?(a) A constitutively active mutant form of PKA in skeletal muscle cells would lead to a decrease in the amount of unphosphorylated phosphorylase kinase.(b) A constitutively active mutant form of PKA in skeletal muscle cells would not increase the affinity of adrenaline for the adrenergic receptor.(c) A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glucose available.(d) A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glycogen available.
a constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glycogen available
Figure Q16-18 shows the pathway through which nitric oxide (NO) triggers smooth muscle relaxation in a blood-vessel wall. Which of the following situations would lead to relaxation of the smooth muscle cells in the absence of acetylcholine?(a) a smooth muscle cell that has a defect in guanylyl cyclase such that it cannot bind NO(b) a muscle cell that has a defect in guanylyl cyclase such that it constitutively converts GTP to cyclic GMP(c) a muscle cell that has cyclic GMP phosphodiesterase constitutively active(d) a drug that blocks an enzyme involved in the metabolic pathway from arginine to NO
a muscle cell that has a defect in guanylyl cyclase such that it constitutively converts GTP to cyclicGMP
You are interested in how cyclic-AMP-dependent protein kinase A (PKA) functions to affect learning and memory, and you decide to study its function in the brain. It is known that, in the cells you are studying, PKA works via a signal transduction pathway like the one depicted in Figure Q16-35. Furthermore, it is also known that activated PKA phosphorylates the transcriptional regulator called Nerd that then activates transcription of the gene Brainy. Which situation described below will lead to an increase in Brainy transcription?(a) a mutation in the Nerd gene that produces a protein that cannot be phosphorylated by PKA(b) a mutation in the nuclear import sequence of PKA from PPKKKRKV to PPAAAAAV(c) a mutation in the gene that encodes cAMP phosphodiesterase that makes the enzyme inactive(d) a mutation in the gene that encodes adenylyl cyclase that renders the enzyme unable to interact with the α subunit of the G protein
a mutation in the gene that encodes cAMP phosphodiesterase that makes the enzyme inactive
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) a mutation that prevents dimerization of the receptor(b) a mutation that destroys the kinase activity of the receptor(c) a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor(d) a mutation that prevents the binding of the normal extracellular signal to the receptor
a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor
After isolating the rough endoplasmic reticulum from the rest of the cytoplasm, you purify the RNAs attached to it. Which of the following proteins do you expect the RNA from the rough endoplasmic reticulum to encode?(a) soluble secreted proteins(b) ER membrane proteins(c) plasma membrane proteins(d) all of the above
all of the above (soluble secreted, ER membrane, and plasma membrane proteins)
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) changing the tyrosines that are normally phosphorylated on RGFR dimerization to alanines(d) changing the tyrosines that are normally phosphorylated on RGFR dimerization to glutamic acid
a mutation that prevents RGFR from binding to RGF
Male cockroaches with mutations that strongly decrease the function of an RTK called RTKX are oblivious to the charms of their female comrades. This particular RTK binds to a small molecule secreted by sexually mature females. Most males carrying loss-of-function mutations in the gene for Ras protein are also unable to respond to females. You have just read a paper in which the authors describe how they have screened cockroaches that are mutant in RTKX for additional mutations that partly restore the ability of males to respond to females. These mutations decrease the function of a protein that the authors call Z. Which of the following types of protein could Z be? Explain your answer.(a) a protein that activates the Ras protein by causing Ras to exchange GDP for GTP(b) a protein that stimulates hydrolysis of GTP by the Ras protein(c) an adaptor protein that mediates the binding of the RTKX to the Ras protein(d) a transcriptional regulator required for the expression of the Ras gene
a protein that stimulates hydrolysis of GTP by the Ras protein
Which of the following statements about the unfolded protein response (UPR) is false?(a) Activation of the UPR results in the production of more ER membrane.(b) Activation of the UPR results in the production of more chaperone proteins.(c) Activation of the UPR occurs when receptors in the cytoplasm sense misfolded proteins.(d) Activation of the UPR results in the cytoplasmic activation of gene regulatory proteins.
activation of the UPR occurs when receptors in the cytoplasm sense misfolded proteins
Molecules to be packaged into vesicles for transport are selected by(a) clathrin.(b) adaptins.(c) dynamin.(d) SNAREs.
adaptins
Which of the following protein families are not involved in directing transport vesicles to the target membrane?(a) SNAREs(b) Rabs(c) tethering proteins(d) adaptins
adaptins
Which of the following statements about transport into mitochondria and chloroplasts is false?(a) The signal sequence on proteins destined for these organelles is recognized by a receptor protein in the outer membrane of these organelles.(b) After a protein moves through the protein translocator in the outer membrane of these organelles, the protein diffuses in the lumen until it encounters a protein translocator in the inner membrane.(c) Proteins that are transported into these organelles are unfolded as they are being transported.(d) Signal peptidase will remove the signal sequence once the protein has been imported into these organelles.
after a protein moves through the protein translocator in the outer membrane of these organelles, the protein diffuses in the lumen until it encounters a protein translocator in the inner membrane
You are interested in further understanding the signal transduction pathway that controls the production of Pig1, a protein important for regulating cell size. Activation of the TRK receptor leads to activation of the GTP-binding protein, Ras, which then activates a protein kinase that phosphorylates the SZE transcription factor. SZE only interacts with the nuclear transport receptor when it is phosphorylated. SZE is a gene activator for the Pig1 gene. This pathway is diagrammed in Figure Q16-50.Normal cells grown under standard conditions (without ligand) are 14 μm in diameter while normal cells exposed to TRK ligand are 10.5 μm in diameter. Given this situation, which of the following conditions do you predict will more likely lead to smaller cells?(a) addition of TRK ligand and a drug that stimulates the GTPase activity of Ras(b) addition of TRK ligand and a drug that inhibits the activity of the phosphatase that acts on SZE(c) addition of TRK ligand and a drug that stimulates the degradation of Pig1(d) addition of TRK ligand and a drug that inhibits Pig1 binding to DNA
addition of TRK ligand and a drug that inhibits the activity of the phosphatase that acts on SZE
Figure Q16-63 shows how normal signaling works with a Ras protein acting downstream of an RTK. You examine a cell line with a constitutively active Ras protein that is always signaling. Which of the following conditions will turn off signaling in this cell line?(a) addition of a drug that prevents protein X from activating Ras(b) addition of a drug that increases the affinity of protein Y and Ras(c) addition of a drug that blocks protein Y from interacting with its target(d) addition of a drug that increases the activity of protein Y
addition of a drug that blocks protein Y from interacting with its target
You are interested in cell-size regulation and discover that signaling through a GPCR called ERC1 is important in controlling cell size in embryonic rat cells. The G protein downstream of ERC1 activates adenylyl cyclase, which ultimately leads to the activation of PKA. You discover that cells that lack ERC1 are 15% smaller than normal cells, while cells that express a mutant, constitutively activated version of PKA are 15% larger than normal cells. Given these results, which of the following treatments to embryonic rat cells should lead to smaller cells?(a) addition of a drug that causes cyclic AMP phosphodiesterase to be hyperactive(b) addition of a drug that prevents GTP hydrolysis by Gα(c) addition of a drug that activates adenylyl cyclase(d) addition of a drug that mimics the ligand of ERC1
addition of a drug that causes cAMP phosphodiesterase to be hyperactive
Acetylcholine binds to a GPCR on heart muscle, making the heart beat more slowly. The activated receptor stimulates a G protein, which opens a K+ channel in the plasma membrane, as shown in Figure Q16-32. Which of the following would enhance this effect of the acetylcholine?(a) addition of a high concentration of a nonhydrolyzable analog of GTP(b) addition of a drug that prevents the α subunit from exchanging GDP for GTP(c) mutations in the acetylcholine receptor that weaken the interaction between the receptor and acetylcholine(d) mutations in the acetylcholine receptor that weaken the interaction between the receptor and the G protein
addition of a high concentration of nonhydrolyzable analog of GTP
When introduced into mitotic cells, which of the following is expected to impair anaphase B but not anaphase A?(a) an antibody against myosin(b) ATPγS, a nonhydrolyzable ATP analog that binds to and inhibits ATPases(c) an antibody against the motor proteins that move from the plus end of microtubules to the minus end(d) an antibody against the motor proteins that move from the minus end of microtubules toward the plus end
an antibody against the motor proteins that move from the minus end of microtubules toward the plus end
Which of the following statements about apoptosis is true?(a) Cells that constitutively express Bcl2 will be more prone to undergo apoptosis.(b) The prodomain of procaspases contains the catalytic activity necessary for procaspase activation.(c) Bax and Bak promote apoptosis by binding to procaspases in the apoptosome.(d) Apoptosis is promoted by the release of cytochrome c into the cytosol from mitochondria.
apoptosis is promoted by the release of Cyt C into the cytosol from the mitochondria
Condensins ________________.(a) are degraded when cells enter M phase.(b) assemble into complexes on the DNA when phosphorylated by M-Cdk.(c) are involved in holding sister chromatids together.(d) bind to DNA before DNA replication begins.
assemble into complexes on the DNA when phosphorylated by M-Cdk
Which of the following precede the re-formation of the nuclear envelope during M phase in animal cells?(a) assembly of the contractile ring(b) decondensation of chromosomes(c) reassembly of the nuclear lamina(d) transcription of nuclear genes
assembly of the contractile ring
In which phase of the cell cycle do cells check to determine whether the DNA is fully and correctly replicated?(a) at the transition between G1 and S(b) when cells enter G0(c) during M(d) at the end of G2
at the end of G2
Most proteins destined to enter the endoplasmic reticulum _________.(a) are transported across the membrane after their synthesis is complete.(b) are synthesized on free ribosomes in the cytosol.(c) begin to cross the membrane while still being synthesized.(d) remain within the endoplasmic reticulum.
begin to cross the membrane while still being synthesized
During the mating process, yeast cells respond to pheromones secreted by other yeast cells. These pheromones bind GPCRs on the surface of the responding cell and lead to the activation of G proteins inside the cell. When a wild-type yeast cell senses the pheromone, its physiology changes in preparation for mating: the cell stops growing until it finds a mating partner. If yeast cells do not undergo the appropriate response after sensing a pheromone, they are considered sterile. Yeast cells that are defective in one or more components of the G protein have characteristic phenotypes in the absence and presence of the pheromone, which are listed in Table 16-34.Which of the following models is consistent with the data from the analysis of these mutants? Explain your answer.(a) α activates the mating response but is inhibited when bound to βγ(b) βγ activates the mating response but is inhibited when bound to α(c) the G protein is inactive; either free α or free βγ complex is capable of activating the mating response(d) the G protein is active; both free α and free βγ complex are required to inhibit the mating response
beta-gamma activates the mating response but it is inhibited when bound to alpha
Programmed cell death occurs ________________.(a) by means of an intracellular suicide program.(b) rarely and selectively only during animal development.(c) only in unhealthy or abnormal cells.(d) only during embryonic development.
by means of intracellular suicide program
Apoptosis differs from necrosis in that necrosis ________________.(a) requires the reception of an extracellular signal.(b) causes DNA to fragment.(c) causes cells to swell and burst, whereas apoptotic cells shrink and condense.(d) involves a caspase cascade.
causes cells to swell and burst, whereas apoptotic cells shrink and condense
Which of the following does not occur during M phase in animal cells?(a) growth of the cell(b) condensation of chromosomes(c) breakdown of nuclear envelope(d) attachment of chromosomes to microtubules
cell growth
You create cells with a version of Cdc6 that cannot be phosphorylated and thus cannot be degraded. Which of the following statements describes the likely consequence of this change in Cdc6?(a) Cells will enter S phase prematurely.(b) Cells will be unable to complete DNA synthesis.(c) The origin recognition complex (ORC) will be unable to bind to DNA.(d) Cdc6 will be produced inappropriately during M phase
cells will be unable to complete DNA synthesis
The principal microtubule-organizing center in animal cells is the ____________.(a) centrosome.(b) centromere.(c) kinetochore.(d) cell cortex
centrosome
Which of the following statements is true?(a) The signal sequences on mitochondrial proteins are usually at the C-terminus.(b) Most mitochondrial proteins are not imported from the cytosol but are synthesized inside the mitochondria.(c) Chaperone proteins in the mitochondria facilitate the movement of proteins across the outer and inner mitochondrial membranes.(d) Mitochondrial proteins cross the membrane in their native, folded state.
chaperone proteins in the mitochondria facilitate the movement of proteins across the inner and outer mitochondrial membranes
Where are proteins in the chloroplast synthesized?(a) in the cytosol(b) in the chloroplast(c) on the endoplasmic reticulum(d) in both the cytosol and the chloroplast
chloroplast and cytosol
Vesicles from the ER enter the Golgi at the ______.(a) medial cisternae.(b) trans Golgi network.(c) cis Golgi network.(d) trans cisternae.
cis Golgi network
Which of the following statements about vesicle budding from the Golgi is false?(a) Clathrin molecules are important for binding to 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 membrane.
clathrin molecules are important for binding to and selecting cargoes for transport
At the end of DNA replication, the sister chromatids are held together by the ___________.(a) kinetochores.(b) securins.(c) cohesins.(d) histones.
cohesins
MPF activity was discovered when cytoplasm from a Xenopus M-phase cell was injected into Xenopus oocytes, inducing the oocytes to form a mitotic spindle. In a control experiment, Xenopus interphase cytoplasm was injected into oocytes and shown not to induce the formation of a mitotic spindle. Which of the following statements is not a legitimate conclusion from the control experiment?(a) The piercing of the oocyte membrane by a needle is insufficient to cause mitotic spindle formation.(b) An increased volume of cytoplasm is insufficient to cause mitotic spindle formation.(c) Injection of extra RNA molecules is insufficient to cause mitotic spindle formation.(d) Components of an interphase nucleus are insufficient to cause mitotic spindle formation.
components of an interphase nucleus are insufficient to cause mitotic spindle formation
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
The activation of the serine/threonine protein kinase Akt requires phosphoinositide 3-kinase (PI 3-kinase) to _________.(a) activate the RTK.(b) create phosphorylated lipids that serve as docking sites that localize Akt to the plasma membrane.(c) directly phosphorylate Akt.(d) to create DAG.
create phosphorylated lipids that serve as docking sites that localize Akt to the plasma membrane
Levels of Cdk activity change during the cell cycle, in part because ________________.(a) the Cdks phosphorylate each other.(b) the Cdks activate the cyclins.(c) Cdk degradation precedes entry into the next phase of the cell cycle.(d) cyclin levels change during the cycle.
cyclin levels change during the cycle
You are working in a biotech company that has discovered a small-molecule drug called H5434. H5434 binds to LDL receptors when they are bound to cholesterol. H5434 binding does not alter the conformation of the LDL receptor's intracellular domain. Interestingly, in vitro experiments demonstrate that addition of H5434 increases the affinity of LDL for cholesterol and prevents cholesterol from dissociating from the LDL receptor even in acidic conditions. Which of the following is a reasonable prediction of what may happen when you add H5434 to cells?(a) Cytosolic cholesterol levels will remain unchanged relative to normal cells.(b) Cytosolic cholesterol levels will decrease relative to normal cells.(c) The LDL receptor will remain on the plasma membrane.(d) The uncoating of vesicles will not occur.
cytosolic cholesterol levels will decrease relative to normal cells
A cell with nuclear lamins that cannot be phosphorylated in M phase will be unable to ________________.(a) reassemble its nuclear envelope at telophase.(b) disassemble its nuclear lamina at prometaphase.(c) begin to assemble a mitotic spindle.(d) condense its chromosomes at prophase.
disassemble its nuclear lamina at prometaphase
The local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by ________________.(a) activating a G protein.(b) activating a receptor tyrosine kinase.(c) diffusing into cells and stimulating the cyclase directly.(d) activating an intracellular protein kinase.
diffusing into cells and stimulating the cyclase directly
Which of the following mechanisms is not directly involved in inactivating an activated RTK?(a) dephosphorylation by serine/threonine phosphatases(b) dephosphorylation by protein tyrosine phosphatases(c) removal of the RTK from the plasma membrane by endocytosis(d) digestion of the RTK in lysosomes
dephosphorylation by serine/threonine phosphatases
Which of the following statements is false?(a) Nucleotides and amino acids can act as extracellular signal molecules.(b) Some signal molecules can bind directly to intracellular proteins that bind DNA and regulate gene transcription.(c) Some signal molecules are transmembrane proteins.(d) Dissolved gases such as nitric oxide (NO) can act as signal molecules, but because they cannot interact with proteins they must act by affecting membrane lipids.
dissolved gases such as NO can act as signal molecules, but because they cannot interact with proteins they must act by affecting membrane lipids
Which of the following statements about disulfide bond formation is false?(a) Disulfide bonds do not form under reducing environments.(b) Disulfide bonding occurs by the oxidation of pairs of cysteine side chains on the protein.(c) Disulfide bonding stabilizes the structure of proteins.(d) Disulfide bonds form spontaneously within the ER because the lumen of the ER is oxidizing.
disulfide bonds form spontaneously within the ER because the lumen of the ER is oxidizing
Cells in the G0 state ________________.(a) do not divide.(b) cannot re-enter the cell cycle.(c) have entered this arrest state from either G1 or G2.(d) have duplicated their DNA.
do not divide
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. He wants to start designing some experiments but wasn't listening carefully when he was told about the molecular defect of this cell line. He's too embarrassed to ask and comes to you for help. He does recall that 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) adaptin
dynamin
Signal sequences that direct proteins to the correct compartment are _________.(a) added to proteins through post-translational modification.(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
The Retinoblastoma (Rb) protein blocks cells from entering the cell cycle by ______.(a) phosphorylating Cdk.(b) marking cyclins for destruction by proteolysis.(c) inhibiting cyclin transcription.(d) activating apoptosis.
inhibiting cyclin transcription
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 receptor across the plasma membrane into the cytosol.(c) A cell-surface receptor capable of binding only one type of signal molecule can mediate only one kind of cell response.(d) Any foreign substance that binds to a receptor for a normal signal molecule will always induce the same response that is produced by that signal molecule on the same cell type.
extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior
Mitogens are _____.(a) extracellular signals that stimulate cell division.(b) transcription factors important for cyclin production.(c) kinases that cause cells to grow in size.(d) produced by mitotic cells to keep nearby neighboring cells from dividing.
extracellular signals that stimulate cell division
The concentration of mitotic cyclin (M cyclin) ________________.(a) rises markedly during M phase.(b) is activated by phosphorylation.(c) falls toward the end of M phase as a result of ubiquitylation and degradation.(d) is highest in G1 phase.
falls toward the M phase as a result of ubiquitylation and degradation
Acetylcholine is a signaling molecule that elicits responses from heart muscle cells, salivary gland cells, and skeletal muscle cells. Which of the following statements is false?(a) Heart muscle cells decrease their rate and force of contraction when they receive acetylcholine, whereas skeletal muscle cells contract.(b) Heart muscle cells, salivary gland cells, and skeletal muscle cells all express an acetylcholine receptor that belongs to the transmitter-gated ion channel family.(c) Active acetylcholine receptors on salivary gland cells and heart muscle cells activate different intracellular signaling pathways.(d) Heart muscle cells, salivary gland cells, and skeletal muscle cells all respond to acetylcholine within minutes of receiving the signal.
heart muscle cells, salivary gland cells, and skeletal muscles all express an acetylcholine receptor that belongs to the transmitter-gated ion channel family
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) dissolved gas.(d) scaffold.
hormone
Which of the following statements about membrane-enclosed organelles is true?(a) In a typical cell, the area of the endoplasmic reticulum membrane far exceeds the area of plasma membrane.(b) The nucleus is the only organelle that is surrounded by a double membrane.(c) Other than the nucleus, most organelles are small and thus, in a typical cell, only about 10% of a cell's volume is occupied by membrane-enclosed organelles; the other 90% of the cell volume is the cytosol.(d) The nucleus is the only organelle that contains DNA.
in a typical cell, the area of the endoplasmic reticulum membrane far exceeds the area of the plasma membrane
Which of the following statements is true?(a) Anaphase A must be completed before anaphase B can take place.(b) In cells in which anaphase B predominates, the spindle will elongate much less than in cells in which anaphase A dominates.(c) In anaphase A, both kinetochore and interpolar microtubules shorten.(d) In anaphase B, microtubules associated with the cell cortex shorten.
in anaphase B, microtubules associated with the cell cortex shorten
Akt promotes the survival of many cells by affecting the activity of Bad and Bcl2, as diagrammed in Figure Q16-58.Which of the following statements is false?(a) In the presence of a survival signal, Akt is phosphorylated.(b) In the absence of a survival signal, Bad inhibits the cell-death inhibitor protein Bcl2.(c) In the presence of a survival signal, the cell-death inhibitory protein Bcl2 is active.(d) In the absence of a survival signal, Bad is phosphorylated.
in the absence of a survival signal, Bad is phosphorylated
In which cellular location would you expect to find ribosomes translating mRNAs that encode ribosomal proteins?(a) the nucleus(b) on the rough ER(c) in the cytosol(d) in the lumen of the ER
in the cytosol
You have isolated a strain of mutant yeast cells that divides normally at 30°C but cannot enter M phase at 37°C. You have isolated its mitotic cyclin and mitotic Cdk and find that both proteins are produced and can form a normal M-Cdk complex at both temperatures. Which of the following temperature-sensitive mutations could not be responsible for the behavior of this strain of yeast?(a) inactivation of a protein kinase that acts on the mitotic Cdk kinase(b) inactivation of an enzyme that ubiquitylates M cyclin(c) inactivation of a phosphatase that acts on the mitotic Cdk kinase(d) a decrease in the levels of a transcriptional regulator required for producing sufficient amounts of M cyclin
inactivation of an enzyme that ubiquitylates M cyclin
All members of the steroid hormone receptor family __________________.(a) are cell-surface receptors.(b) do not undergo conformational changes.(c) are found only in the cytoplasm.(d) interact with signal molecules that diffuse through the plasma membrane.
interact with signal molecules that diffuse through the plasma membrane
Foreign substances like nicotine, morphine, and menthol exert their initial effects by _____.(a) killing cells immediately, exerting their physiological effects by causing cell death.(b) diffusing through cell plasma membranes and binding to transcription factors to change gene expression.(c) interacting with cell-surface receptors, causing the receptors to transduce signal inappropriately in the absence of the normal stimulus.(d) removing cell-surface receptors from the plasma membrane.
interacting with cell-surface receptors, causing the receptors to transduce signal inappropriately in the absence of the normal stimulus
The G1 DNA damage checkpoint ________________.(a) causes cells to proceed through S phase more quickly.(b) involves the degradation of p53.(c) is activated by errors caused during DNA replication.(d) involves the inhibition of cyclin-Cdk complexes by p21.
involves the inhibition of cyclin-Cdk complexes by p21
A protein kinase can act as an integrating device in signaling if it ___________________.(a) phosphorylates more than one substrate.(b) catalyzes its own phosphorylation.(c) is activated by two or more proteins in different signaling pathways.(d) initiates a phosphorylation cascade involving two or more protein kinases.
is activated by two or more proteins in different signaling pathways
What is the role of the nuclear localization sequence in a nuclear protein?(a) It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore.(b) It is a hydrophobic sequence that enables the protein to enter the nuclear membranes.(c) It aids in protein unfolding so that the protein can thread through nuclear pores.(d) It prevents the protein from diffusing out of the nucleus through nuclear pores.
it is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore
Which of the following statements about the anaphase-promoting complex (APC) is false?(a) It promotes the degradation of proteins that regulate M phase.(b) It inhibits M-Cdk activity.(c) It is continuously active throughout the cell cycle.(d) M-Cdk stimulates its activity.
it is continuously active throughout the cell cycle
How does S-Cdk help guarantee that replication occurs only once during each cell cycle?(a) It blocks the rise of Cdc6 concentrations early in G1.(b) It phosphorylates and inactivates DNA helicase.(c) It phosphorylates the Cdc6 protein, marking it for destruction.(d) It promotes the assembly of a prereplicative complex.
it phosphorylates the Cdc6 protein, marking it for destruction
Which of the following statements about kinetochores is true?(a) Kinetochores assemble onto chromosomes during late prophase.(b) Kinetochores contain DNA-binding proteins that recognize sequences at the telomere of the chromosome.(c) Kinetochore proteins bind to the tubulin molecules at the minus end of microtubules.(d) Kinetochores assemble on chromosomes that lack centromeres.
kinetochores assemble onto chromosomes during late prophase
Which of the following organelles is not part of the endomembrane system?(a) Golgi apparatus(b) the nucleus(c) mitochondria(d) lysosomes
mitochondria
Which of the following statements about peroxisomes is false?(a) Most peroxisomal proteins are synthesized in the ER.(b) Peroxisomes synthesize phospholipids for the myelin sheath.(c) Peroxisomes produce hydrogen peroxide.(d) Vesicles that bud from the ER can mature into peroxisomes.
most peroxisomal proteins are synthesized in the ER
Which of the following statements is false?(a) Cytokinesis in plant cells is mediated by the microtubule cytoskeleton.(b) Small membrane vesicles derived from the Golgi apparatus deliver new cell-wall material for the new wall of the dividing cell.(c) The phragmoplast forms from the remains of interpolar microtubules of the mitotic spindle.(d) Motor proteins walking along the cytoskeleton are important for the contractile ring that guides formation of the new cell wall.
motor proteins walking along the cytoskeleton are important for the contractile ring that guides formation of the new cell wall
Disassembly of the nuclear envelope ________________.(a) causes the inner nuclear membrane to separate from the outer nuclear membrane.(b) results in the conversion of the nuclear envelope into protein-free membrane vesicles.(c) is triggered by the phosphorylation of integrins.(d) must occur for kinetochore microtubules to form in animal cells.
must occur for kinetochore microtubules to form in animal cells
Which of the following statements about nuclear transport is true?(a) mRNAs and proteins transit the nucleus through different types of nuclear pores.(b) Nuclear import receptors bind to proteins in the cytosol and bring the proteins to the nuclear pores, where the proteins are released from the receptors into the pores for transit into the nucleus.(c) Nuclear pores have water-filled passages that small, water-soluble molecules can pass through in a nonselective fashion.(d) Nuclear pores are made up of many copies of a single protein.
nuclear pores have water-filled passages that small, water-soluble molecules can pass through in a non-selective fashion
Your friend works in a biotechnology company and has discovered a drug that blocks the ability of Ran to exchange GDP for GTP. What is the most likely effect of this drug on nuclear transport?(a) Nuclear transport receptors would be unable to bind cargo.(b) Nuclear transport receptors would be unable to enter the nucleus.(c) Nuclear transport receptors would be unable to release their cargo in the nucleus.(d) Nuclear transport receptors would interact irreversibly with the nuclear pore fibrils.
nuclear transport receptors would be unable to release their cargo in the nucleus
Different glycoproteins can have a diverse array of oligosaccharides. Which of the statements below about this diversity is true?(a) Extensive modification of oligosaccharides occurs in the extracellular space.(b) Different oligosaccharides are covalently linked to proteins in the ER and the Golgi.(c) A diversity of oligosaccharyl transferases recognizes specific protein sequences, resulting in the linkage of a variety of oligosaccharides to proteins.(d) Oligosaccharide diversity comes from modifications that occur in the ER and the Golgi of the 14-sugar oligosaccharide added to the protein in the ER.
oligosaccharide diversity comes from modifications that occur in the ER and the golgi of the 14-sugar oligosaccharide added to the protein in the ER
Which of the following statements about the cell cycle is false?(a) Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic cells.(b) An unfavorable environment can cause cells to arrest in G1.(c) A cell has more DNA during G2 than it did in G1.(d) The cleavage divisions that occur in an early embryo have short G1 and G2 phases.
once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic cells
Which of the following statements about phagocytic cells in animals is false?(a) Phagocytic cells are important in the gut to take up large particles of food.(b) Phagocytic cells scavenge dead and damaged cells and cell debris.(c) Phagocytic cells can engulf invading microorganisms and deliver them to their lysosomes for destruction.(d) Phagocytic cells extend pseudopods that surround the material to be ingested.
phagocytic cells are important in the gut to take up large particles of food
Which of the following statements about molecular switches is false?(a) Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off.(b) Protein kinases transfer the terminal phosphate from ATP onto a protein.(c) Serine/threonine kinases are the most common types of protein kinase.(d) A GTP-binding protein exchanges its bound GDP for GTP to become activated.
phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off
Which of the following statements is true?(a) Proteins destined for the ER are translated by a special pool of ribosomes whose subunits are always associated with the outer ER membrane.(b) Proteins destined for the ER translocate their associated mRNAs into the ER lumen where they are translated.(c) Proteins destined for the ER are translated by cytosolic ribosomes and are targeted to the ER when a signal sequence emerges during translation.(d) Proteins destined for the ER are translated by a pool of cytosolic ribosomes that contain ER-targeting sequences that interact with ER-associated protein translocators.
proteins destined for the ER are translated by cytosolic ribosomes and are targeted to the ER when a signal sequence emerges during translation
Which of the following statements about the protein quality control system in the ER is false?(a) Chaperone proteins help misfolded proteins fold properly.(b) Proteins that are misfolded are degraded in the ER lumen.(c) Protein complexes are checked for proper assembly before they can exit the ER.(d) A chaperone protein will bind to a misfolded protein to retain it in the ER.
proteins that are misfolded are degraded in the ER lumen
Which of the following statements about the endoplasmic reticulum (ER) is false?(a) The ER is the major site for new membrane synthesis in the cell.(b) Proteins to be delivered to the ER lumen are synthesized on smooth ER.(c) Steroid hormones are synthesized on the smooth ER.(d) The ER membrane is contiguous with the outer nuclear membrane.
proteins to be delivered to the ER lumen are synthesized on smooth ER
Cell lines A and B both survive in tissue culture containing serum but do not proliferate. Factor F is known to stimulate proliferation in cell line A. Cell line A produces a receptor protein (R) that cell line B does not produce. To test the role of receptor R, you introduce this receptor protein into cell line B, using recombinant DNA techniques. You then test all of your various cell lines in the presence of serum for their response to factor F, with the results summarized in Table Q16-1.Which of the following cannot be concluded from your results above?(a) Binding of factor F to its receptor is required for proliferation of cell line A.(b) Receptor R binds to factor F to induce cell proliferation in cell line A.(c) Cell line A expresses a receptor for factor F.(d) Factor F is not required for proliferation in cell line B.
receptor R binds to factor F to induce cell proliferation in cell line A
Cytokinesis in animal cells ________________.(a) requires ATP.(b) leaves a small circular "scar" of actin filaments on the inner surface of the plasma membrane.(c) is often followed by phosphorylation of integrins in the plasma membrane.(d) is assisted by motor proteins that pull on microtubules attached to the cell cortex.
requires ATP
Which of the following statements about a protein in the lumen of the ER is false?(a) A protein in the lumen of the ER is synthesized by ribosomes on the ER membrane.(b) Some of the proteins in the lumen of the ER can end up in the extracellular space.(c) Some of the proteins in the lumen of the ER can end up in the lumen of an organelle in the endomembrane system.(d) Some of the proteins in the lumen of the ER can end up in the plasma membrane.
some of the proteins in the lumen of the ER can end up in the plasma membrane
A large protein that passes through the nuclear pore must have an appropriate _________.(a) sorting sequence, which typically contains the positively charged amino acids lysine and arginine.(b) sorting sequence, which typically contains the hydrophobic amino acids leucine and isoleucine.(c) sequence to interact with the nuclear fibrils.(d) Ran-interacting protein domain.
sorting sequence, which typically contains the positively charged amino acids lysine and arginine
Which of the following statements about vesicular membrane fusion is false?(a) Membrane fusion does not always immediately follow vesicle docking.(b) The hydrophilic surfaces of membranes have water molecules associated with them that must be displaced before vesicle fusion can occur.(c) The GTP hydrolysis of the Rab proteins provides the energy for membrane fusion.(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.
the GTP hydrolysis of Rab proteins provides the energy for membrane fusion
The length of time a G protein will signal is determined by _______.(a) the activity of phosphatases that turn off G proteins by dephosphorylating Gα.(b) the activity of phosphatases that turn GTP into GDP.(c) the degradation of the G protein after Gα separates from Gβγ(d) the GTPase activity of Gα
the GTPase activity of Galpha
Which of the following statements is false?(a) Mitotic Cdk must be phosphorylated by an activating kinase (Cak) before it is active.(b) Phosphorylation of mitotic Cdk by the inhibitory kinase (Wee1) makes the Cdk inactive, even if it is phosphorylated by the activating kinase.(c) Active M-Cdk phosphorylates the activating phosphatase (Cdc25) in a positive feedback loop.(d) The activating phosphatase (Cdc25) removes all phosphates from mitotic Cdk so that M-Cdk will be active.
the activating phosphatase (Cdc25) removes all phosphates from mitotic Cdk so that M-Cdk will be active
The following happens when a G-protein-coupled receptor activates a G protein.(a) The β subunit exchanges its bound GDP for GTP.(b) The GDP bound to the α subunit is phosphorylated to form bound GTP.(c) The α subunit exchanges its bound GDP for GTP.(d) It activates the α subunit and inactivates the βγ complex.
the alpha subunit exchanges its bound GDP for GTP
N-linked oligosaccharides on secreted glycoproteins are attached to(a) nitrogen atoms in the polypeptide backbone.(b) the serine or threonine in the sequence Asn-X-Ser/Thr.(c) the N-terminus of the protein.(d) the asparagine in the sequence Asn-X-Ser/Thr.
the asparagine in the sequence Asn-X-Ser/Thr
Progression through the cell cycle requires a cyclin to bind to a Cdk because _________.(a) the cyclins are the molecules with the enzymatic activity in the complex.(b) the binding of a cyclin to Cdk is required for Cdk enzymatic activity.(c) cyclin binding inhibits Cdk activity until the appropriate time in the cell cycle.(d) without cyclin binding, a cell-cycle checkpoint will be activated.
the binding of a Cdk is required for Cdk enzymatic activity
Which of the following descriptions is consistent with the behavior of a cell that lacks a protein required for a checkpoint mechanism that operates in G2?(a) The cell would be unable to enter M phase.(b) The cell would be unable to enter G2.(c) The cell would enter M phase under conditions when normal cells would not.(d) The cell would pass through M phase more slowly than normal cells
the cell would enter M phase under normal conditions when normal cells would not
What would be the most obvious outcome of repeated cell cycles of S and M phase only? (a) Cells would not be able to replicate their DNA.(b) The mitotic spindle could not assemble.(c) Cells would get larger and larger.(d) The cells produced would get smaller and smaller.
the cells would get smaller and smaller
When Ras is activated, cells will divide. A dominant-negative form of Ras clings too tightly to GDP. You introduce a dominant-negative form of Ras into cells that also have a normal version of Ras. Which of the following statements is true?(a) The cells you create will divide less frequently than normal cells in response to the extracellular signals that typically activate Ras.(b) The cells you create will run out of the GTP necessary to activate Ras.(c) The cells you create will divide more frequently compared to normal cells in response to the extracellular signals that typically activate Ras.(d) The normal Ras in the cells you create will not be able to bind GDP because the dominant-negative Ras binds to GDP too tightly.
the cells you create will divide less frequently than normal cells in response to the extracellular signals that typically activate Ras
Which of the following statements is false?(a) The cleavage furrow is a puckering of the plasma membrane caused by the constriction of a ring of filaments attached to the plasma membrane.(b) The cleavage furrow will not begin to form in the absence of a mitotic spindle.(c) The cleavage furrow always forms perpendicular to the interpolar microtubules.(d) The cleavage furrow always forms in the middle of the cell.
the cleavage furrow always forms in the middle of the cell
Proteins that are fully translated in the cytosol and lack a sorting signal will end up in ____.(a) the cytosol.(b) the mitochondria.(c) the interior of the nucleus.(d) the nuclear membrane.
the cytosol
Which of the following statements about G-protein-coupled receptors (GPCRs) is false?(a) GPCRs are the largest family of cell-surface receptors in humans.(b) GPCRs are used in endocrine, paracrine, and neuronal signaling.(c) GPCRs are found in yeast, mice, and humans.(d) The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains.
the diff. classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains
Activated protein kinase C (PKC) can lead to the modification of the membrane lipids in the vicinity of the active PKC. Figure Q16-38 shows how G proteins can indirectly activate PKC. You have discovered the enzyme activated by PKC that mediates the lipid modification. You call the enzyme Rafty and demonstrate that activated PKC directly phosphorylates Rafty, activating it to modify the plasma membrane lipids in the vicinity of the cell where PKC is active; these lipid modifications can be detected by dyes that bind to the modified lipids. Cells lacking Rafty do not have these modifications, even when PKC is active. Which of the following conditions would lead to signal-independent modification of the membrane lipids by Rafty?(a) the expression of a constitutively active phospholipase C(b) a mutation in the GPCR that binds the signal more tightly(c) a Ca2+ channel in the endoplasmic reticulum with an increased affinity for IP3(d) a mutation in the gene that encodes Rafty such that the enzyme can no longer be phosphorylated by PKC
the expression of a constitutively active phospholipase C
A friend declares that chromosomes are held at the metaphase plate by microtubules that push on each chromosome from opposite sides. Which of the following observations does not support your belief that the microtubules are pulling on the chromosomes?(a) the jiggling movement of chromosomes at the metaphase plate(b) the way in which chromosomes behave when the attachment between sister chromatids is severed(c) the way in which chromosomes behave when the attachment to one kinetochore is severed(d) the shape of chromosomes as they move toward the spindle poles at anaphase
the jiggling movement of chromosomes at the metaphase plate
Which of the following statements is false?(a) DNA synthesis begins at origins of replication.(b) The loading of the origin recognition complexes (ORCs) is triggered by S-Cdk.(c) The phosphorylation and degradation of Cdc6 help to ensure that DNA is replicated only once in each cell cycle.(d) DNA synthesis can only begin after prereplicative complexes assemble on the ORCs.
the loading of the ORCs is triggered S-Cdk
Which of the following statements about secretion is true?(a) The membrane of a secretory vesicle will fuse with the plasma membrane when it discharges its contents to the cell's exterior.(b) Vesicles for regulated exocytosis will not bud off the trans Golgi network until the appropriate signal has been received by the cell.(c) The signal sequences of proteins destined for constitutive exocytosis ensure their packaging into the correct vesicles.(d) Proteins destined for constitutive exocytosis aggregate as a result of the acidic pH of the trans Golgi network.
the membrane of a secretory vesicle will fuse with the plasma membrane when it discharges its contents to the cell's exterior
Which of the following statements is true?(a) The mitotic spindle is largely made of intermediate filaments.(b) The contractile ring is made largely of microtubules and actin filaments.(c) The contractile ring divides the nucleus in two.(d) The mitotic spindle helps segregate the chromosomes to the two daughter cells.
the mitotic spindle helps segregate the chromosomes to the two daughter cells
Which of the following statements is true?(a) Lysosomes are believed to have originated from the engulfment of bacteria specialized for digestion.(b) The nuclear membrane is thought to have arisen from the plasma membrane invaginating around the DNA.(c) Because bacteria do not have mitochondria, they cannot produce ATP in a membrane-dependent fashion.(d) Chloroplasts and mitochondria share their DNA.
the nuclear membrane is thought to have arisen from the plasma membrane invaginating around the DNA
Cells have oligosaccharides displayed on their cell surface that are important for cell-cell recognition. Your friend discovered a transmembrane glycoprotein, GP1, on a pathogenic yeast cell that is recognized by human immune cells. He decides to purify large amounts of GP1 by expressing it in bacteria. To his purified protein he then adds a branched 14-sugar oligosaccharide to the asparagine of the only Asn-X-Ser sequence found on GP1 (Figure Q15-48). Unfortunately, immune cells do not seem to recognize this synthesized glycoprotein. Which of the following statements is a likely explanation for this problem?(a) The oligosaccharide should have been added to the serine instead of the asparagine.(b) The oligosaccharide should have been added one sugar at a time.(c) The oligosaccharide needs to be further modified before it is mature.(d) The oligosaccharide needs a disulfide bond.
the oligosaccharide needs to be further modified before it is mature
Which of the following statements is true?(a) Because endocrine signals are broadcast throughout the body, all cells will respond to the hormonal signal.(b) The regulation of inflammatory responses at the site of an infection is an example of paracrine signaling.(c) Paracrine signaling involves the secretion of signals into the bloodstream for distribution throughout the organism.(d) The axons of neurons typically signal target cells using membrane-bound signaling molecules that act on receptors in the target cells.
the regulation of inflammatory responses at the site of an infection is an example of paracrine signaling
Proteins that are fully translated in the cytosol do not end up in _______.(a) the cytosol.(b) the mitochondria.(c) the interior of the nucleus.(d) transport vesicles.
transport vesicles
The ethylene response in plants involves a dimeric transmembrane receptor. When the receptor is not bound to ethylene, the receptor binds to and activates a protein kinase, which activates an intracellular signaling pathway that leads to the degradation of a transcriptional regulator important for transcribing the ethylene-responsive genes (see Figure Q16-60). You discover a phosphatase that is important for ethylene signaling, and you name it PtpE. Plants lacking PtpE never turn on ethylene-responsive genes, even in the presence of ethylene. You find that PtpE dephosphorylates serine 121 on the transcriptional regulator. Furthermore, plants lacking PtpE degrade the transcriptional regulator in the presence of ethylene. Which of the following statements is inconsistent with your data?(a) When the transcriptional regulator is phosphorylated, it activates transcription of the ethylene-responsive genes.(b) When the transcriptional regulator is not phosphorylated, it binds to DNA.(c) Activation of the protein kinase that binds to the ethylene receptor leads to inactivation of PtpE.(d) Binding of ethylene to its receptor leads to the activation of PtpE.
when the transcriptional regulator is not phosphorylated, it binds to DNA
Figure Q15-57 shows the orientation of the Krt1 protein on the membrane of a Golgi-derived vesicle that will fuse with the plasma membrane. Given this diagram, which of the following statements is true?(a) When this vesicle fuses with the plasma membrane, the entire Krt1 protein will be secreted into the extracellular space.(b) When this vesicle fuses with the plasma membrane, the C-terminus of Krt1 will be inserted into the plasma membrane.(c) When this vesicle fuses with the plasma membrane, the N-terminus of Krt1 will be in the extracellular space.(d) When this vesicle fuses with the plasma membrane, the N-terminus of Krt1 will be cytoplasmic.
when this vesicle fuses with the plasma membrane, the N-terminus of Krt1 will be in the extracellular space
An individual transport vesicle(a) contains only one type of protein in its lumen.(b) will fuse with only one type of membrane.(c) is endocytic if it is traveling toward the plasma membrane.(d) is enclosed by a membrane with the same lipid and protein composition as the membrane of the donor organelle.
will fuse with only one type of membrane
Which of the following is not good direct evidence that the cell-cycle control system is conserved through billions of years of divergent evolution?(a) A yeast cell lacking a Cdk function can use the human Cdk to substitute for its missing Cdk during the cell cycle.(b) The amino acid sequences of cyclins in plants are similar to the amino acid sequences of cyclins in humans.(c) The Cdk proteins in humans share conserved phosphorylation sites with the Cdk proteins in yeast.(d) Yeast cells have only one Cdk, whereas humans have many Cdks.
yeast cells have only one Cdk, whereas humans have many Cdks