Chp. 15
Which does NOT normally occur at a nuclear pore complex? (A) A protein complex is imported into the nucleus. (B) A protein containing a nuclear localization signal enters the pore from the cytosol at the same time that a protein containing a nuclear export signal exits the pore from the nucleus. (C) An mRNA molecule is exported to the cytosol. (D) A nuclear import receptor is exported to the cytosol. (E) All of the above are common occurrences. (F) None of the above are common occurrences.
(E) All of the above are common occurrences.
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.
(b) Cytosolic cholesterol levels will decrease relative to normal cells.
Which of the following is true? A common pool of ribosomes is used to synthesize both the proteins that stay in the cytosol and those that are destined for the ER. A special class of ribosomes embedded in the ER translates the proteins destined for that organelle. All ribosomes are attached to the ER when they begin synthesizing a protein. most proteins are synthesized inside the smooth ER
A common pool of ribosomes is used to synthesize both the proteins that stay in the cytosol and those that are destined for the ER.
Which organelle is essentially a small sac of digestive enzymes that functions in degrading worn-out organelles as well as macromolecules and particles taken into the cell by endocytosis? A lysosome A peroxisome An endosome The endoplasmic reticulum The Golgi apparatus
A lysosome
Which organelle contains enzymes used in a variety of oxidative reactions that break down lipids and destroy toxic molecules? A lysosome A mitochondrion A peroxisome An endosome The endoplasmic reticulum
A peroxisome
Which organelle sorts ingested molecules and recycles some of them back to the plasma membrane? A lysosome A peroxisome An endosome The endoplasmic reticulum The Golgi apparatus
An endosome
Which mechanism is used for degrading obsolete parts of a cell, such as a defective mitochondrion? Apoptosis Autophagy Exocytosis Phagocytosis The unfolded protein responses
Autophagy
The interiors of the ER, Golgi apparatus, endosomes, and lysosomes communicate with each other in which of the following ways? By excreting hormones and other small signaling molecules By fusing with one another. By open pores that allow ions to exit and enter the organelle By small vesicles that bud off of one organelle and fuse with another They do not communicate with one another.
By small vesicles that bud off of one organelle and fuse with another
Which type of protein binds to improperly folded or improperly assembled proteins in the ER, holding them there until proper folding occurs? Antibody proteins Chaperone proteins ER retention signal Glycosylating proteins Tethering proteins
Chaperone proteins
at proteins can assemble into a basketlike network that gives budding vesicles their shape? Adaptin Clathrin Dynamin Rab proteins SNAREs
Clathrin
Which best describes a potential pathway followed by a protein destined for secretion? Cytosol → ER → Golgi apparatus → transport vesicle → endosome → secretory vesicle → plasma membrane Cytosol → ER → secretory vesicle → plasma membrane Cytosol → ER → transport vesicle → Golgi apparatus → transport vesicle → plasma membrane ER → Golgi apparatus → secretory vesicle → plasma membrane ER → Golgi apparatus → transport vesicle → endosome → secretory vesicle → plasma membrane
Cytosol → ER → transport vesicle → Golgi apparatus → transport vesicle → plasma membrane
nadh produced in the cytosolic enter the mitochondrion via A) a ligand gated channel B) membrane permeability C) A NADH specific transporter D) None of the above E) an NADH channel
D
The movement of materials from the plasma membrane, through endosomes, and then to lysosomes, describes which type of pathway? Endocytic pathway Endolytic pathway Endosomal pathway Exocytic pathway Secretory pathway
Endocytic pathway
Proteins enter which organelle as they are being synthesized? Chloroplast Endoplasmic reticulum Mitochondrion Nucleus Peroxisome
Endoplasmic reticulum
Which cellular compartment acts as the main sorting station for extracellular cargo molecules taken up by endocytosis? Endosomes Lysosomes The Golgi apparatus Transport vesicles
Endosomes
Which of the following pathways does NOT deliver materials directly to lysosomes? Autophagy Endocytosis Exocytosis Phagocytosis Pinocytosis
Exocytosis
Which of the following organelles is not surrounded by a double membrane? Chloroplast Golgi apparatus Mitochondrion Nucleus
Golgi apparatus
Which of the following is NOT true of receptor-mediated endocytosis? In receptor-mediated endocytosis, extracellular substances are internalized in clathrin-coated vesicles. In receptor-mediated endocytosis, internalized vesicles fuse with lysosomes, which then mature into endosomes. Low-density lipoproteins (LDLs) are taken into cells by receptor-mediated endocytosis. Some viruses are taken into the cell by receptor-mediated endocytosis.
In receptor-mediated endocytosis, internalized vesicles fuse with lysosomes, which then mature into endosomes.
In the process of translocating a polypeptide across the membrane of the endoplasmic reticulum, a stop-transfer sequence halts the process. What eventually becomes of the stop-transfer sequence? It forms an α-helical membrane-spanning segment of the protein. It is cleaved from the protein. It is translocated into the lumen of the endoplasmic reticulum. It remains in the cytosol.
It forms an α-helical membrane-spanning segment of the protein.
What would happen to a protein that is engineered to contain both a nuclear localization signal and a nuclear export signal? It would be unable to fold properly and would be targeted for destruction. It would bind to nuclear import receptors and nuclear export receptors, forming a nonfunctional complex. It would shuttle in and out of the nucleus. It would spend most of its time in the cytosol. It would spend most of its time in the nucleus.
It would shuttle in and out of the nucleus.
Which statement about receptor-mediated endocytosis of LDL particles is true? LDL receptors are normally degraded in the lysosome along with LDL. LDL receptors are not taken up by receptor-mediated endocytosis unless they are carrying LDL. LDL receptors in the plasma membrane associate with clathrin-coated pits. Mutations that impair the endocytosis of LDL receptors cause a drop in blood cholesterol levels. The high pH inside endosomes allows LDL to dissociate from its receptor.
LDL receptors in the plasma membrane associate with clathrin-coated pits.
Which of the following is true of lysosomes? Lysosomal enzymes are optimally active in the acidic conditions maintained within lysosomes. Lysosomes form from vesicles that pinch off from the endoplasmic reticulum. Lysosomes have a pH that is higher than that of the cytosol. Most of the lysosomal membrane proteins have glycosylated regions on the cytosolic side of the membrane. The products of digestion in lysosomes leave the lysosome by transport vesicles.
Lysosomal enzymes are optimally active in the acidic conditions maintained within lysosomes.
Which proteins bind to nuclear localization signals on newly synthesized proteins? Cytosolic fibrils Nuclear export receptors Nuclear import receptors Nuclear pore proteins Signal-recognition particles
Nuclear import receptors
In the unfolded protein response, the accumulation of misfolded proteins in the ER serves as a signal for the cell to do which of the following? Export the misfolded proteins to the cytosol Glycosylate the misfolded protein Produce more ER membrane and ER proteina
Produce more ER membrane and ER proteina
Mitochondria and peroxisomes do NOT have what in common? Proteins need to unfold to enter them. Their membranes contain a protein translocator. They are present in eukaryotic cells. They must import proteins to function.
Proteins need to unfold to enter them.
In a typical human secretory cell, which of the following membranes has the largest surface area? Lysosomes Nuclear inner membrane Plasma membrane Rough ER Smooth ER
Rough ER
Which proteins play a central role in the fusion of a vesicle with a target membrane? Adaptin proteins Clathrin proteins Rab proteins SNARE proteins Tethering proteins
SNARE proteins
In muscle cells, which organelle sequesters Ca2+ from the cytosol? Endosomes Lysosomes Mitochondria Peroxisomes Smooth ER
Smooth ER
Which organelle cannot receive proteins directly from the cytosol? Chloroplast Mitochondrion Nucleus Peroxisome The Golgi apparatus
The Golgi apparatus
Which organelle receives proteins and lipids from the endoplasmic reticulum, modifies them, and then dispatches them to other destinations in the cell? A mitochondrion A peroxisome An endosome The Golgi apparatus The nucleus
The Golgi apparatus
Proteins that lack a sorting signal remain as permanent residents of which part of a eukaryotic cell? A lysosome The cytosol The endoplasmic reticulum The Golgi apparatus The nucleus
The cytosol
The outer membrane of the nucleus is continuous with the membrane of which other organelle? Endosomes Mitochondria Peroxisomes The endoplasmic reticulum The Golgi apparatus
The endoplasmic reticulum
Where in the cell are some proteins initially decorated with an oligosaccharide tree on asparagine residues? Mitochondria Peroxisomes The cytosol The endoplasmic reticulum The Golgi apparatus
The endoplasmic reticulum
Which organelle is the major site of new membrane synthesis in a cell? A mitochondrion A peroxisome The endoplasmic reticulum The Golgi apparatus The nucleus
The endoplasmic reticulum
Proteins have to unfold during their transport across the membranes of all but which of the following organelles? Chloroplasts Mitochondria The endoplasmic reticulum The nucleus
The nucleus
Which membrane-enclosed organelles most likely evolved in a similar manner? Chloroplasts and peroxisomes Mitochondria and the ER Mitochondria and the Golgi apparatus Mitochondria and the nucleus The nucleus and the ER
The nucleus and the ER
Ricin is one of the most powerful toxins known. The protein consists of two subunits: the A chain is an enzyme that inhibits translation and the B chain is a lectin that binds to carbohydrates on the cell surface. What is the most likely mechanism by which ricin enters the cell? The A chain binds to clathrin. The A chain stimulates autophagy. The B chain interacts with SNAREs. The protein enters through pore complexes in the plasma membrane. The protein is internalized by endocytosis.
The protein is internalized by endocytosis.
Investigators have engineered a gene that encodes a protein bearing an ER signal sequence followed by a nuclear localization signal. What would be the likely fate of that protein? Because of its conflicting signals, the protein will be degraded in the cytosol. Because of the conflicting signals, the protein will remain in the cytosol. The protein will be recognized by a nuclear import receptor and escorted into the nucleus. The protein will be recognized by an SRP and enter the ER. The protein will be sent to a lysosome for destruction.
The protein will be recognized by an SRP and enter the ER.
Which of the following statements is NOT true of mitochondrial proteins that are synthesized in the cytosol? Chaperone proteins help draw the proteins inside the mitochondrion. The proteins are unfolded as they are transported into the mitochondria. The proteins cross both the inner and outer mitochondrial membranes as they are imported. The proteins must be transported across the mitochondrial membranes while being synthesized. The proteins usually have a signal sequence at their N-terminus.
The proteins must be transported across the mitochondrial membranes while being synthesized.
What distinguishes proteins destined for regulated secretion? Their surface properties allow them to form aggregates that are packaged into secretory vesicles. They are cleaved from membrane domains in the Golgi apparatus prior to being packed into secretory vesicles. They are produced in small amounts and then concentrated in secretory vesicles. They bind to clathrin. They have a series of amino acids that acts as a tag that marks them for packaging into secretory vesicles.
Their surface properties allow them to form aggregates that are packaged into secretory vesicles.
Proteins entering the cis Golgi network can do which of the following? They are either sent to the nucleus or to the plasma membrane for secretion. They are sorted according to whether they are destined for lysosomes or for the cell surface. They can either move backward through the Golgi stack or be sent to the plasma membrane. They can either move onward through the Golgi stack or be returned to the ER.
They can either move onward through the Golgi stack or be returned to the ER.
hich of the following is NOT a role for the oligosaccharides on glycosylated proteins? They can guide the protein to the appropriate organelle by serving as a transport signal for packaging the protein into appropriate transport vesicles. They can protect the protein from degradation and hold it in the ER until it is properly folded. They can provide a source of energy for the cell. When displayed on the cell surface, oligosaccharides form part of the cell's carbohydrate layer. When displayed on the cell surface, they promote cell-cell recognition.
They can provide a source of energy for the cell.
How can proteins travel from one cisterna to the next in the Golgi apparatus? Through bridges that link the cisternae Through osmosis Through pores in the membranes of cisternae Through transport vesicles that bud from one cisterna and fuse with the next Through transporters in the membranes of cisternae
Through transport vesicles that bud from one cisterna and fuse with the next
Which molecule is displaced when a vesicle and its target membrane fuse? Cholesterol Phospholipids SNAREs Tethering proteins Water
Water
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.
a
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.
a
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.
a
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.
a
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.
a
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.
a
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.
a
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.
a
Lysosomal enzymes are directed to lysosomes by: a C-terminal, hydrophobic, membrane-spanning amino acid sequence. a phosphorylated sugar group. an N-terminal signal sequence. their ability to fold properly and function at high pH. their ability to fold properly and function at low pH.
a phosphorylated sugar group.
The final products of the digestion of macromolecules: are expelled from the lysosome by H+ pumps in the lysosomal membrane. are removed from the lysosome by transport vesicles that carry them to where they are needed. are secreted from the cell when lysosomes fuse with the plasma membrane. are transferred to the cytosol through transporters in the lysosomal membrane. are ultimately destroyed by lysosomal enzymes.
are transferred to the cytosol through transporters in the lysosomal membrane.
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.
b
Molecules to be packaged into vesicles for transport are selected by ________. (a) clathrin. (b) adaptins. (c) dynamin. (d) SNAREs.
b
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.
b
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
b
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.
b
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.
b
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
c
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.
c
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.
c
Vesicles from the ER enter the Golgi at the ______. (a) medial cisternae. (b) trans Golgi network. (c) cis Golgi network. (d) trans cisternae.
c
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
c
Which of the following organelles is not part of the endomembrane system? (a) Golgi apparatus (b) the nucleus (c) mitochondria (d) lysosomes
c
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.
c
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.
c
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.
c
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.
c
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.
c
Your friend has just joined a lab that studies vesicle budding from the Golgi and has been given a cell line that does not form mature vesicles. 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
c
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.
c
The low pH inside endosomes: causes cargo proteins to bind to their receptors. causes internalized receptors to release their cargo. destroys internalized cargo proteins. destroys internalized receptors.
causes internalized receptors to release their cargo.
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
d
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.
d
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.
d
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.
d
Which of the following choices reflects the appropriate order of locations through which a protein destined for the plasma membrane travels? (a) lysosome endosome plasma membrane (b) ER lysosome plasma membrane (c) Golgi lysosome plasma membrane (d) ER Golgi plasma membrane
d
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
d
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.
d
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.
d
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.
d
Eukaryotic cells continually ingest bits of their plasma membrane, along with small amounts of extracellular fluid. The lost pieces of membrane are replaced by the process of: endocytosis. exocytosis. phagocytosis. pinocytosis.
exocytosis.
The ER signal sequence on a growing polypeptide chain is recognized by a signal-recognition particle (SRP) in the cytosol. This interaction: cleaves the ER signal sequence from the polypeptide chain. guides the ribosome and its polypeptide to the ER membrane. releases the polypeptide chain from the ribosome. speeds the synthesis of the polypeptide chain.
guides the ribosome and its polypeptide to the ER membrane.
Most mitochondrial and chloroplast proteins are made: in the cell cytosol. in the endoplasmic reticulum. in the Golgi apparatus. within the mitochondrion or chloroplast.
in the cell cytosol.
Phagocytic cells include: macrophages and neutrophils. neutrophils and red blood cells. protozoa and bacteria. red blood cells and liver cells.
macrophages and neutrophils.
Human cells ingest large particles by: macrocytosis. nutricytosis. phagocytosis. pinocytosis. pseudocytosis.
phagocytosis.
Proteins with no signal sequence that are made in the cytosol: are degraded by proteases. are returned to their organelle of origin. are secreted. are taken up by a lysosome. remain in the cytosol.
remain in the cytosol.
Proteins in the cytosol that are destined for other organelles must first enter: the endoplasmic reticulum. the Golgi apparatus. the lysosomes. the nucleus.
the endoplasmic reticulum.
If a signal sequence is removed from an ER protein: the protein can enter any organelle other than the ER the protein will be escorted to the ER by chaperone proteins. the protein will be immediately degraded. the protein will be unable to exit the ER. the protein will remain in the cytosol.
the protein will remain in the cytosol.
In the endocrine cells of the adrenal gland, steroid hormones are synthesized in: the Golgi apparatus. the cytosol. the nucleus. the rough ER. the smooth ER.
the smooth ER.
