Exam 2
Which of the following factors would tend to increase membrane fluidity? A) a greater proportion of unsaturated phospholipids B) a greater proportion of saturated phospholipids C) a lower temperature D) a relatively high protein content in the membrane E) a greater proportion of relatively large glycolipids compared with lipids having smaller molecular masses
A. A greater proportion of unsaturated phospholipids
Which of the following crosses lipid bilayers the slowest? A) a sodium ion B) a small, polar molecule like water C) a large, polar molecule like glucose D) a small, nonpolar molecule like oxygen (O2)
A. A sodium ion
A membrane protein that spans the phospholipid bilayer one or more times is ________. A) a transmembrane protein B) an associated protein C) a peripheral protein D) an integrin E) a glycoprotein
A. A transmembrane protein
Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly? A) CO2 B) an amino acid C) glucose D) K+ E) starch
A. CO2
Centrioles, cilia, flagella, and basal bodies have remarkably similar structural elements and arrangements. Which of the following hypotheses is most plausible in light of such structural similarities? A) Cilia and flagella arise from centrioles. B) Loss of basal bodies should prevent cells from dividing in two. C) Motor proteins such as dynein must have evolved before any of these four kinds of structure. D) Cilia and flagella evolved separately in the same ancestral eukaryotic organism. E) Natural selection for cell motility repeatedly selected for microtubular arrays in circular patterns in the evolution of each of these structures.
A. Cilia and flagella arise from centrioles
In some cells, there are many ion electrochemical gradients across the plasma membrane even though there are usually only one or two proton pumps present in the membrane. The gradients of the other ions are most likely accounted for by ________. A) cotransport proteins B) ion channels C) pores in the plasma membrane D) passive diffusion across the plasma membrane E) cellular metabolic reactions that create or destroy ions
A. Cotransport Proteins
The evolution of eukaryotic cells most likely involved ________. A) endosymbiosis of an aerobic bacterium in a larger host cell-the endosymbiont evolved into mitochondria B) anaerobic archaea taking up residence inside a larger bacterial host cell to escape toxic oxygen-the anaerobic bacterium evolved into chloroplasts C) an endosymbiotic fungal cell evolving into the nucleus D) acquisition of an endomembrane system and subsequent evolution of mitochondria from a portion of the Golgi apparatus
A. Endosymbiosis of an aerobic bacterium in a larger host cell- the endosymbiont evolved into mitochondria
Five dialysis bags constructed of membrane, which is permeable to water and impermeable to sucrose, were filled with various concentrations of sucrose and then placed in separate beakers containing an initial concentration of 0.6 M sucrose solution. At 10-minute intervals, the bags were massed (weighed) and the percentage change in mass of each bag was graphed. Which line in the graph represents the bag with the highest initial concentration of sucrose? A) A B) B C) C D) D E) E
A. Increasing Exponential
The membranes of winter wheat are able to remain fluid when it is extremely cold by ________. A) increasing the percentage of unsaturated phospholipids in the membrane B) increasing the percentage of cholesterol molecules in the membrane C) decreasing the number of hydrophobic proteins in the membrane D) cotransport of glucose and hydrogen E) using active transport
A. Increasing the percentage of unsaturated phospholipids in the membrane
Rhodopsins are light-sensitive molecules composed of a protein (opsin) and retinal (derivative of vitamin A). Opsin is a membrane protein with several α-helical segments that loop back and forth through the plasma membrane. There are two classes of rhodopsins. According to Oded Beje, one class has relatively slow dynamics (a photocycle of approximately 0.5 second) and is well suited for light detection. The second class has faster dynamics (a photocycle of approximately 0.02 seconds) and is well suited for chemiosmosis: pumping of protons or chloride ions across cell membranes. Oded Beje was the first, in September 2000, to report on a rhodopsin (proteorhodopsin) found in the domain Bacteria. Refer to the paragraph on rhodopsins. Which of the following best describes this particular protein? A) integral B) peripheral C) external D) internal
A. Integral
What is the most important factor in explaining why osmosis occurs spontaneously? A) It leads to an increase in entropy. B) It leads to a decrease in entropy. C) The process is exothermic. D) The process is endothermic.
A. It leads to an increase in entropy
What is the function of the nuclear pore complex found in eukaryotes? A) It regulates the movement of proteins and RNAs into and out of the nucleus. B) It synthesizes the proteins required to copy DNA and make mRNA. C) It selectively transports molecules out of the nucleus but prevents all inbound molecules from entering the nucleus. D) It assembles ribosomes from raw materials that are synthesized in the nucleus.
A. It regulates the movement of proteins and RNAs into and out of the nucleus
Which of the following contains hydrolytic enzymes? A) lysosome B) vacuole C) mitochondrion D) Golgi apparatus E) peroxisome
A. Lysosome
Movement of vesicles within the cell depends on what cellular structures? A) microtubules and motor proteins B) actin filaments and microtubules C) actin filaments and ribosomes D) centrioles and motor proteins E) actin filaments and motor proteins
A. Microtubules and motor proteins
Cyanide binds with at least one molecule involved in producing ATP. If a cell is exposed to cyanide, most of the cyanide will be found within the ________. A) mitochondria B) ribosomes C) peroxisomes D) lysosomes E) endoplasmic reticulum
A. Mitochondria
The text states that ribonucleotides can diffuse through some types of liposomes. It is likely that the lipids present early in chemical evolution had short chains. Would liposomes formed from these types of lipids be more or less permeable to ribonucleotides than if early cells formed from long-chained lipids? A) more permeable B) less permeable C) same permeability
A. More permeable
Why is the smooth endoplasmic reticulum unable to synthesize proteins? A) No ribosomes are attached to its surface. B) There is no supply of free amino acids that it can easily access. C) It stores calcium, which is a known inhibitor of protein synthesis. D) It has no DNA to direct synthesis of proteins.
A. No ribosomes are attached to its surface
You have a planar bilayer with equal amounts of saturated and unsaturated phospholipids. After testing the permeability of this membrane to glucose, you increase the proportion of unsaturated phospholipids in the bilayer. What will happen to the membrane's permeability to glucose? A) Permeability to glucose will increase. B) Permeability to glucose will decrease. C) Permeability to glucose will stay the same. D) You cannot predict the outcome; you simply have to make the measurement.
A. Permeability to glucose will increase.
Which structure is the site of the synthesis of proteins that may be exported from the cell? A) rough ER B) lysosomes C) plasmodesmata D) Golgi vesicles E) free cytoplasmic ribosomes
A. Rough ER
Proteins coded for by nuclear DNA but found within mitochondria move from the cytoplasm into mitochondria using ________. A) signal sequences (peptides) B) random transport vesicles C) attachment of ribosomes to outer mitochondrial pores and direct deposition into the inner mitochondrial compartment D) mRNAs that are manufactured in the nucleus but translated by mitochondrial ribosomes
A. Signal sequences (peptides)
Which aspect of phospholipids is most important to the formation of bilayers? A) They are amphipathic. B) Their polar heads can interact with water. C) The length of their hydrocarbon tails can be altered to modulate membrane fluidity. D) Their hydrocarbon tails can consist of fatty acids or isoprene subunits.
A. They are amphipathic
The presence of cholesterol in the plasma of some animal cells ___. A) enables the membranes to stay fluid when cell temperature drops B) enables the cell to remove hydrogen atoms from saturated phospholipids C) enables the cell to add hydrogen atoms to unsaturated phospholipids D) makes the cell membrane less flexible, allowing it to sustain greater intracellular pressure E) reduces mutations to genetic material inside the cell
A. enables the membranes to stay fluid when cell temp. drops
In what way do the membranes of a eukaryotic cell vary? A) Phospholipids are found only in certain membranes. B) Certain proteins are unique to each membrane. C) Only certain membranes of the cell are selectively permeable. D) Only certain membranes are constructed from amphipathic molecules. E) Some membranes have hydrophobic surfaces exposed to the cytoplasm, while others have hydrophilic surfaces facing the cytoplasm.
B. Certain proteins are unique to each membrane
Thylakoids, DNA, and ribosomes are all components found in ________. A) vacuoles B) chloroplasts C) mitochondria D) lysosomes E) nuclei
B. Chloroplasts
You make a phospholipid bilayer with short, saturated hydrocarbon tails. You measure the permeability of this membrane to oxygen. You then double the length of the hydrocarbon tails and remeasure membrane permeability. You then double the length of the hydrocarbon tails again and make a third measurement of membrane permeability. You graph membrane permeability as a function of hydrocarbon tail length. Which of the accompanying graphs best represents the data you expect?
B. Decreasing Linear Line
Lysosomes that lack mannose-6-phosphate receptors ________. A) receive "modified" enzymes and are thus unable to break down carbohydrates B) do not receive enzyme shipments from the Golgi apparatus C) have unstable membranes D) stick to transport vesicles and impede the transfer of enzymes
B. Do not receive enzyme shipments from the Golgi apparatus
Which of the following is a major difference between prokaryotic cells and eukaryotic cells? A) Prokaryotes have cells but eukaryotes do not. B) Eukaryotic cells have more intracellular organelles than prokaryotes. C) Prokaryotes are not able to carry out aerobic respiration, relying instead on anaerobic metabolism. D) Prokaryotes are generally larger than eukaryotes.
B. Eukaryotic cells have more intracellular organelles than prokaryotes
Five dialysis bags constructed of membrane, which is permeable to water and impermeable to sucrose, were filled with various concentrations of sucrose and then placed in separate beakers containing an initial concentration of 0.6 M sucrose solution. At 10-minute intervals, the bags were massed (weighed) and the percentage change in mass of each bag was graphed. Which line or lines in the graph represent(s) bags that contain a solution that is hypertonic at 50 minutes? A) A and B B) B C) C D) D E) D and E
B. Increasing Linear
Which of the following is a characteristic feature of a carrier protein in a plasma membrane? A) It is a peripheral membrane protein. B) It exhibits a specificity for a particular type of molecule. C) It requires the expenditure of cellular energy to function. D) It works against diffusion. E) It has no hydrophobic regions.
B. It exhibits a specificity for a particular type of molecule
What can you infer about a high-molecular-weight protein that cannot be transported into the nucleus? A) It is too large. B) It lacks a nuclear localization signal (NLS). C) It contains errors in its amino acid sequence. D) It lacks a signal sequence.
B. It lacks a nuclear localization signal (NLS)
A cell with a predominance of free ribosomes is most likely ________. A) primarily producing proteins for secretion B) primarily producing proteins in the cytosol C) constructing an extensive cell wall or extracellular matrix D) digesting large food particles E) enlarging its vacuole
B. Primarily producing proteins in the cytosol
Which of the following is present in a prokaryotic cell? A) mitochondrion B) ribosome C) nuclear envelope D) chloroplast E) ER
B. Ribosome
The solutions in the arms of a U-tube are separated at the bottom of the tube by a selectively permeable membrane. The membrane is permeable to sodium chloride but not to glucose. Side A is filled with a solution of 0.4 M glucose and 0.5 M sodium chloride (NaCl), and side B is filled with a solution containing 0.8 M glucose and 0.4 M sodium chloride. Initially, the volume in both arms is the same. Refer to the figure. At the beginning of the experiment, A) side A is hypertonic to side B. B) side A is hypotonic to side B. C) side A is isotonic to side B. D) side A is hypertonic to side B with respect to glucose. E) side A is hypotonic to side B with respect to NaCl.
B. Side A is hypotonic to Side B
The liver is involved in detoxification of many poisons and drugs. Which of the following structures is primarily involved in this process and, therefore, abundant in liver cells? A) rough ER B) smooth ER C) Golgi apparatus D) nuclear envelope E) transport vesicles
B. Smooth ER
If you mechanically shook a mixture of phospholipids and water, what would you expect to see when you observe the solution using an electron microscope? A) The lipids and water will have separated into two distinct layers because the lipids are partially nonpolar. B) Some lipids will have formed tiny vesicles filled with water. C) All the lipids will have formed planar bilayer membranes. D) Most lipids will have completely dissolved in solution because they are partially polar.
B. Some lipids will have formed tiny vessicles filled with water.
A cell with an extensive area of smooth endoplasmic reticulum is specialized to ________. A) play a role in storage B) synthesize large quantities of lipids C) actively export protein molecules D) import and export protein molecules
B. Synthesize large quantities of lipids
Scientists have found that polypeptides which are normally synthesized in the endoplasmic reticulum are about 20 amino acids longer when they are synthesized by ribosomes not attached to the endoplasmic reticulum. What is a possible explanation for the greater length of these polypeptides? A) Ribosomes attached to the endoplasmic reticulum require fewer amino acids to function. B) The 20 amino acids serve as a signal (peptide) sequence that directs the forming polypeptides to the endoplasmic reticulum, where they are cleaved off during processing. C) The 20-amino-acid sequence helps the endoplasmic reticulum package these proteins for shipping to the Golgi. D) The protein has a different function in the cytosol than in the endoplasmic reticulum.
B. The 20 amino acids serve as a signal (peptide) seq. that directs the forming polypeptides to the endoplasmic reticulum, where they are cleaved off during processing
Steroid hormones are large communication molecules that are modified cholesterol molecules. How do you think they enter a cell? A) Their size probably allows them to diffuse through the plasma membrane. B) Their lipid nature probably allows them to diffuse through the plasma membrane. C) Their protein structure probably allows them to diffuse through the plasma membrane. D) They must require a protein transporter, because the plasma membrane is completely impermeable to molecules.
B. Their lipid nature probably allows them to diffuse through the plasma membrane
Eukaryotic cells manufacture cytoskeletal proteins, which help to maintain cell shapes and functions. What would you predict about these proteins? A) They initially contain signal sequences that allow their entrance into the endoplasmic reticulum. B) They are manufactured on free ribosomes in the cytoplasm. C) They are glycosylated in the Golgi apparatus. D) They travel to the nucleus in a transport vesicle with a specific signal.
B. They are manufactured on free ribosomes in the cytoplasm
Which organelle often takes up much of the volume of a plant cell? A) lysosome B) vacuole C) mitochondrion D) Golgi apparatus E) peroxisome
B. Vacuole
Under what circumstances does membrane transport require energy? A) wherever large molecules are moved within a cell B) whenever a solute is moved against its electrochemical gradient C) whenever an ion moves through a phospholipid bilayer membrane D) whenever oxygen moves through a phospholipid bilayer membrane
B. Whenever a solute is moved against its electrochemical gradient
Gramicidin is an antibiotic that increases the permeability of bacterial cell walls to inorganic ions. What is the most likely mode of action of gramicidin? A) It acts by active transport. B) It causes membranes to fuse with one another. C) It forms a channel in the membrane. D) It removes electrical charges from solutes.
C. It forms a channel in the membrane
Which organelle is the primary site of ATP synthesis in eukaryotic cells? A) lysosome B) vacuole C) mitochondrion D) Golgi apparatus E) peroxisome
C. Mitochondrion
The nuclear lamina is an array of filaments on the inner side of the nuclear membrane. If a method were found that could cause the lamina to fall into disarray, what would you most likely expect to be the immediate consequence? A) the loss of all nuclear function B) the inability of the nucleus to divide during cell division C) a change in the shape of the nucleus D) failure of chromosomes to carry genetic information E) inability of the ribosomes to produce proteins
C. A change in the shape of the nucleus
Which of the following is NOT found in a prokaryote? A) DNA B) a cell wall C) a mitochondrion D) a plasma membrane
C. A mitochondrion
A number of systems for pumping ions across membranes are powered by ATP. Such ATP-powered pumps are often called ATPases, although they do not often hydrolyze ATP unless they are simultaneously transporting ions. Because small increases in calcium ions in the cytosol can trigger a number of different intracellular reactions, cells keep the cytosolic calcium concentration quite low under normal conditions, using ATP-powered calcium pumps. For example, muscle cells transport calcium from the cytosol into the membranous system called the sarcoplasmic reticulum (SR). If a resting muscle cell's cytosol has a free calcium ion concentration of 10−7 while the concentration in the SR is 10−2, then how is the ATPase acting? A) ATPase activity must be powering an inflow of calcium from the outside of the cell into the SR. B) ATPase activity must be transferring i to the SR to enable this to occur. C) ATPase activity must be pumping calcium from the cytosol to the SR against the concentration gradient. D) ATPase activity must be opening a channel for the calcium ions to diffuse back into the SR along the concentration gradient. E) ATPase activity must be routing calcium ions from the SR to the cytosol and then to the cell's environment.
C. ATPase activity must be pumping calcium from the cytosol to the SR against the concentration gradient
For a protein to be an integral membrane protein, it would have to be ________. A) hydrophilic B) hydrophobic C) amphipathic, with at least one hydrophobic region D) completely covered with phospholipids E) exposed on only one surface of the membrane
C. Amphipathic, with at least one hydrophobic region
Lysosomes are considered to be part of the endomembrane system because they ________. A) deposit end-products of digestion in the endoplasmic reticulum B) facilitate movement between stacks of the Golgi C) are formed from products synthesized by the endoplasmic reticulum and processed by the Golgi D) are composed largely of phospholipids
C. Are formed from products synthesized bu the endoplasmic reticulum and processed by the Golgi
Which of the following is the best explanation for why cholesterol decreases the permeability of biological membranes? A) Cholesterol binds to the outside surface of a membrane, thus blocking the movement of solutes. B) Because cholesterol is amphipathic, it forms tiny vesicles that trap solutes. C) Because cholesterol is amphipathic, it fits in between the phospholipids and blocks diffusion through the membrane. D) Cholesterol has four rings in its structure that can sequester ("trap") solutes.
C. Because cholesterol is amphipathic, it gits in between the phospholipids and blocks diffusion through the membrane.
The difference in lipid and protein composition between the membranes of the endomembrane system is largely determined by the ________. A) interconnection of most intracellular membranes to the nuclear envelope B) transportation of membrane lipids among the membranes of the endomembrane system by small membrane vesicles C) function of the Golgi apparatus in sorting and directing membrane components D) modification of the membrane components once they reach their final destination E) synthesis of different lipids and proteins in each of the organelles of the endomembrane system
C. Function of the Golgi apparatus in sorting and directing membrane components
Five dialysis bags constructed of membrane, which is permeable to water and impermeable to sucrose, were filled with various concentrations of sucrose and then placed in separate beakers containing an initial concentration of 0.6 M sucrose solution. At 10-minute intervals, the bags were massed (weighed) and the percentage change in mass of each bag was graphed. Which line in the graph represents the bag that contained a solution isotonic to the 0.6 M solution at the beginning of the experiment? A) A B) B C) C D) D E) E
C. Horizontal Line
Which of the following is TRUE of osmosis? A) Osmosis only takes place in red blood cells. B) Osmosis is an energy-demanding or "active" process. C) In osmosis, water moves across a membrane from areas of lower solute concentration to areas of higher solute concentration. D) In osmosis, solutes move across a membrane from areas of lower water concentration to areas of higher water concentration.
C. In osmosis, water moves across a membrane from areas of lower concentration to areas of higher solute concentration
Celery stalks that are immersed in freshwater for several hours become stiff. Similar stalks left in a 0.15 M salt solution become limp. From this we can deduce that the freshwater ________. A) and the salt solution are both hypertonic to the cells of the celery stalks B) and the salt solution are both hypotonic to the cells of the celery stalks C) is hypotonic and the salt solution is hypertonic to the cells of the celery stalks D) is hypertonic and the salt solution is hypotonic to the cells of the celery stalks E) is isotonic and the salt solution is hypertonic to the cells of the celery stalks
C. Is hypotonic and the salt solution is hypertonic to the cells of the celery stalks
Which plant cell organelle contains its own DNA and ribosomes? A) glyoxysome B) vacuole C) mitochondrion D) Golgi apparatus E) peroxisome
C. Mitochondrion
Which of the following membrane activities requires energy from ATP? A) facilitated diffusion of chloride ions across the membrane through a chloride channel B) movement of water into a cell C) movement of Na+ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid D) movement of glucose molecules into a bacterial cell from a medium containing a higher concentration of glucose than that inside the cell E) movement of carbon dioxide out of a paramecium
C. Movement of Na+ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid
Suppose a cell has the following molecules and structures: enzymes, DNA, ribosomes, plasma membrane, and mitochondria. It could be a cell from ________. A) a bacterium B) an animal but not a plant C) nearly any eukaryotic organism D) a plant but not an animal E) any kind of prokaryotic organism
C. Nearly any eukaryotic organism
In receptor-mediated endocytosis, receptor molecules initially project to the outside of the cell. Where do they end up after endocytosis? A) on the outside of vesicles B) on the inside surface of the cell membrane C) on the inside surface of the vesicle D) on the outer surface of the nucleus E) on the ER
C. On the inside surface of the vesicle
Which of the following affects the osmolarity of a solution? I) concentration of cations II) concentration of anions III) concentration of water A) only I B) only III C) only I and II D) only II and III E) I, II, and III
C. Only I and II
Which of the following types of molecules are the major structural components of the cell membrane? A) phospholipids and cellulose B) nucleic acids and proteins C) phospholipids and proteins D) proteins and cellulose E) glycoproteins and cholesterol
C. Phospholipids and Proteins
Large numbers of ribosomes are present in cells that specialize in producing which of the following molecules? A) lipids B) glycogen C) proteins D) cellulose E) nucleic acids
C. Proteins
Which type of organelle or structure is primarily involved in the synthesis of oils, phospholipids, and steroids? A) ribosome B) lysosome C) smooth endoplasmic reticulum D) mitochondrion E) contractile vacuole
C. Smooth endoplasmic reticulum
Tay-Sachs disease is a human genetic abnormality that results in cells accumulating and becoming clogged with very large, complex, undigested lipids. Which cellular organelle must be involved in this condition? A) the endoplasmic reticulum B) the Golgi apparatus C) the lysosome D) mitochondrion E) membrane-bound ribosomes
C. The lysosome
You have just discovered an organism that lives in extremely cold environments. Which of the following would you predict to be TRUE about the phospholipids in its membranes, compared to phospholipids in the membranes of organisms that live in warmer environments? A) The membrane phospholipids of cold-adapted organisms will have longer hydrocarbon tails. B) The membrane phospholipids of cold-adapted organisms will have more saturated hydrocarbon tails. C) The membrane phospholipids of cold-adapted organisms will have more unsaturated hydrocarbon tails.
C. The membrane phospholipids of cold - adapted organisms will have more unsaturated hydrocarbon tails
A patient was involved in a serious accident and lost a large quantity of blood. In an attempt to replenish body fluids, distilled water—equal to the volume of blood lost—is added to the blood directly via one of his veins. What will be the most probable result of this transfusion? A) It will have no unfavorable effect as long as the water is free of viruses and bacteria. B) The patient's red blood cells will shrivel up because the blood has become hypotonic compared to the cells. C) The patient's red blood cells will swell and possibly burst because the blood has become hypotonic compared to the cells. D) The patient's red blood cells will shrivel up because the blood has become hypertonic compared to the cells. E) The patient's red blood cells will burst because the blood has become hypertonic compared to the cells.
C. The patients red blood cells will swell and possibly burst because the blood has become hypotonic compared to the cells
Which of the following macromolecules leaves the nucleus of a eukaryotic cell through pores in the nuclear membrane? A) DNA B) amino acids C) mRNA D) phospholipids
C. mRNA
When a potassium ion (K+) moves from the soil into the vacuole of a cell on the surface of a root, it must pass through several cellular structures. Which of the following correctly describes the order in which these structures will be encountered by the ion? A) plasma membrane → primary cell wall → cytoplasm → vacuole B) secondary cell wall → plasma membrane → primary cell wall → cytoplasm → vacuole C) primary cell wall → plasma membrane → cytoplasm → vacuole D) primary cell wall → plasma membrane → lysosome → cytoplasm → vacuole E) primary cell wall → plasma membrane → cytoplasm → secondary cell wall → vacuole
C. primary cell wall → plasma membrane → cytoplasm → vacuole
The solutions in the arms of a U-tube are separated at the bottom of the tube by a selectively permeable membrane. The membrane is permeable to sodium chloride but not to glucose. Side A is filled with a solution of 0.4 M glucose and 0.5 M sodium chloride (NaCl), and side B is filled with a solution containing 0.8 M glucose and 0.4 M sodium chloride. Initially, the volume in both arms is the same. Refer to the figure. If you examine side A after three days, you should find ________. A) a decrease in the concentration of NaCl and glucose and an increase in the water level B) a decrease in the concentration of NaCl, an increase in the water level, and no change in the concentration of glucose C) no net change in the system D) a decrease in the concentration of NaCl and a decrease in the water level E) no change in the concentration of NaCl and glucose and an increase in the water level
D. A decrease in the concentration of NaCl and a decrease in the water level
Which of the following crosses lipid bilayers the fastest? A) a sodium ion B) a small, polar molecule like water C) a large, polar molecule like glucose D) a small, nonpolar molecule like oxygen (O2)
D. A small, nonpolar molecule like oxygen (O2)
A biologist ground up some plant leaf cells and then centrifuged the mixture to fractionate the organelles. Organelles in one of the heavier fractions could produce ATP in the light, whereas organelles in the lighter fraction could produce ATP in the dark. The heavier and lighter fractions are most likely to contain, respectively, ________. A) mitochondria and chloroplasts B) chloroplasts and peroxisomes C) peroxisomes and chloroplasts D) chloroplasts and mitochondria E) mitochondria and peroxisomes
D. Chloroplasts and Mitochondria
Motor proteins provide for molecular motion in cells by interacting with what types of cellular structures? A) mitochondria and chloroplasts B) membrane proteins of the inner nuclear envelope C) free ribosomes and ribosomes attached to the ER D) components of the cytoskeleton E) cellulose fibers in the cell wall
D. Components of the cytoskeleton
What is the most likely pathway taken by a newly synthesized protein that will be secreted by a cell? A) ER → Golgi → nucleus B) Golgi → ER → lysosome C) nucleus → ER → Golgi D) ER → Golgi → vesicles that fuse with plasma membrane E) ER → lysosomes → vesicles that fuse with plasma membrane
D. ER → Golgi → vesicles that fuse with plasma membrane
Where are proteins produced other than on ribosomes free in the cytosol or ribosomes attached to the ER? A) in the extracellular matrix B) in the Golgi apparatus C) in lysosomes D) in mitochondria E) in the nucleolus
D. In Mitochondria
In a plant cell, DNA may be found ________. A) only in the nucleus B) only in the nucleus and mitochondria C) only in the nucleus and chloroplasts D) in the nucleus, mitochondria, and chloroplasts E) in the nucleus, mitochondria, chloroplasts, and peroxisomes
D. In the nucleus, mitochondria, and chloroplasts, and peroxisomes
Which of the following increases the strength of the hydrophobic interactions in lipid bilayers and thus makes them less permeable to polar molecules? A) the presence of double bonds B) increasing temperature C) removing cholesterol D) increasing length of the hydrocarbon chains
D. Increasing lengths of the hydrocarbon chains
Since structure correlates well with function, look for new ways to probe the complex structure of proteins in order to understand what they do and how they do it. One of the most powerful techniques in existence today is X-ray crystallography. The main difficulty with this technique is getting the protein to crystallize. Once crystallized, the protein is bombarded with X-rays to create a pattern that can be analyzed mathematically to determine the three-dimensional structure of the protein. This analysis has been performed by Palczewski (2000) on the protein rhodopsin, which is a light-sensitive protein found in species ranging from ancient bacteria (archaea) to humans. The structure (schematically shown above, where each letter represents an amino acid) is characterized by a single polypeptide chain with several α-helical segments that loop back and forth across the cell membrane. Another notable feature is the disulfide bond (—S—S—) that can be seen at the bottom of the third transmembrane segment. Which term best describes the type of membrane protein in the figure? A) peripheral B) external C) internal D) integral
D. Integral
When a membrane is freeze-fractured, the bilayer splits down the middle between the two layers of phospholipids. In an electron micrograph of a freeze-fractured membrane, the bumps seen on the fractured surface of the membrane are ________. A) peripheral proteins B) phospholipids C) carbohydrates D) integral proteins E) cholesterol molecules
D. Integral Proteins
In an experiment involving planar bilayers, a solution of table salt (sodium and chloride ions in water) is added on the left side of the membrane while pure water is added on the right side. After 30 minutes, the researchers test for the presence of ions on each side of the membrane. The right side tests negative for ions. What can you conclude? A) The experiment failed. B) The water somehow blocked the movement of ions across the membrane. C) The left side would probably also test negative for ions. D) Ions cannot cross planar bilayers.
D. Ions cannot cross planar bilayers
Asbestos is a material that was once used extensively in construction. One risk from working in a building that contains asbestos is the development of asbestosis caused by the inhalation of asbestos fibers. Cells will phagocytize asbestos but are not able to degrade it. As a result, asbestos fibers accumulate in ________. A) mitochondria B) ribosomes C) peroxisomes D) lysosomes
D. Lysosomes
Suppose a young boy is always tired and fatigued, suffering from a metabolic disease. Which of the following organelles is most likely involved in this disease? A) lysosomes B) Golgi apparatus C) ribosomes D) mitochondria
D. Mitochondria
When yeast cells are transferred from anaerobic to aerobic growth conditions, which of these organelles become much more numerous? A) lysosomes B) Golgi apparatus C) ribosomes D) mitochondria
D. Mitochondria
Which structure is common to plant and animal cells? A) chloroplast B) wall made of cellulose C) central vacuole D) mitochondrion E) centriole
D. Mitochondrion
Which of the following processes includes all others? A) osmosis B) diffusion of a solute across a membrane C) facilitated diffusion D) passive transport E) transport of an ion down its electrochemical gradient
D. Passive transport
Which of the following produces and modifies polysaccharides that will be secreted? A) lysosome B) vacuole C) mitochondrion D) Golgi apparatus E) peroxisome
D. Peroxisome
An organism with a cell wall would most likely be unable to take in materials through ________. A) diffusion B) osmosis C) active transport D) phagocytosis E) facilitated diffusion
D. Phagocytosis
Lipids that form membranes have what kind of structure? A) polar heads and polar tails, which allows them to interact with water on both sides of the membrane B) completely polar, which allows them to dissolve in water C) polar heads and nonpolar tails; the nonpolar tails interact with water D) polar heads and nonpolar tails; the polar heads interact with water
D. Polar heads and nonpolar tails; the polar heads interact with water.
A primary objective of cell fractionation (including differential centrifugation) is to ________. A) view the structure of cell membranes B) sort cells based on their size and weight C) determine the size of various organelles D) separate the major organelles E) separate lipid-soluble from water-soluble molecules
D. Separate the major organelles
Where would you most likely find an integral membrane protein? A) on the inside surface of the cell membrane B) on the outside surface of the cell membrane C) floating freely in the cytoplasm D) spanning the cell membrane, with parts of the protein visible from both the inside and the outside of the cell
D. Spanning the cell membrane, with parts of the protein visible from both the inside and the outside of the cell
You make a phospholipid bilayer with short, saturated hydrocarbon tails. You measure the permeability of this membrane to oxygen. You are going to change the length of the hydrocarbon tails and remeasure membrane permeability, but first your boss asks you to graph the data you expect if there is no effect of hydrocarbon tail length on membrane permeability (your null hypothesis). Which of the accompanying graphs best represents the data you expect if your null hypothesis is correct?
D. Straight Horizontal Line
In a bacterium, we will find DNA in ________. A) a membrane-enclosed nucleus B) mitochondria C) the endoplasmic reticulum D) the nucleoid E) ribosomes
D. The nucleoid
Ions diffuse across membranes through specific ion channels down ________. A) their chemical gradients B) their concentration gradients C) their electrical gradients D) their electrochemical gradients E) the osmotic potential gradients
D. Their electrochemical gradients
Why are lipids and proteins free to move laterally in membranes? A) The interior of the membrane is filled with liquid water. B) Lipids and proteins repulse each other in the membrane. C) Hydrophilic portions of the lipids are in the interior of the membrane. D) There are only weak hydrophobic interactions in the interior of the membrane. E) Molecules such as cellulose can pull them in various directions.
D. There are only weak hydrophobic interactions in the interior of the membrane
Which of the following is most likely TRUE of a protein that cotransports glucose and sodium ions into the intestinal cells of an animal? A) Sodium and glucose compete for the same binding site in the cotransporter. B) Glucose entering the cell down its concentration gradient provides energy for uptake of sodium ions against the electrochemical gradient. C) Sodium ions can move down their electrochemical gradient through the cotransporter whether or not glucose is present outside the cell. D) The cotransporter can also transport potassium ions. E) A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose.
E. A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose
The Golgi apparatus has a polarity, or sidedness, to its structure and function. Which of the following statements correctly describes this polarity? A) Transport vesicles fuse with one side of the Golgi and leave from the opposite side. B) Proteins in the membrane of the Golgi may be sorted and modified as they move from one side of the Golgi to the other. C) Lipids in the membrane of the Golgi may be sorted and modified as they move from one side of the Golgi to the other. D) Soluble proteins in the cisternae (interior) of the Golgi may be sorted and modified as they move from one side of the Golgi to the other. E) All of the listed responses correctly describe polarity characteristics of the Golgi function.
E. All of the listed responses correctly describe polarity characteristics of the Golgi function
All of the following are part of a prokaryotic cell EXCEPT ________. A) DNA B) a cell wall C) a plasma membrane D) ribosomes E) an endoplasmic reticulum
E. An endoplasmic reticulum
Which of the following allows water to move much faster across cell membranes? A) the hydrophobic interior of a cell membrane B) the sodium—potassium pump C) ATP D) peripheral proteins E) aquaporins
E. Aquaporins
The phosphate transport system in bacteria imports phosphate into the cell even when the concentration of phosphate outside the cell is much lower than the cytoplasmic phosphate concentration. Phosphate import depends on a pH gradient across the membrane-more acidic outside the cell than inside the cell. Phosphate transport is an example of ________. A) passive diffusion B) facilitated diffusion C) active transport D) osmosis E) cotransport
E. Cotransport
Glucose diffuses slowly through artificial phospholipid bilayers. The cells lining the small intestine, however, rapidly move large quantities of glucose from the glucose-rich food into their glucose-poor cytoplasm. Using this information, which transport mechanism is most probably functioning in the intestinal cells? A) simple diffusion B) phagocytosis C) active transport pumps D) exocytosis E) facilitated diffusion
E. Facilitated Diffusion
Which of the following correctly matches a component of the cytoskeleton to one of its functions? A) Microfilaments form the nuclear lamina. B) Microtubules help animal cells divide in two. C) Microfilaments cause ciliary bending. D) Intermediate filaments contribute to cytoplasmic streaming. E) Microtubules move chromosomes.
E. Microtubules move chromosomes
Which animal cell organelle contains enzymes that transfer hydrogen from various substrates to oxygen? A) lysosome B) vacuole C) mitochondrion D) Golgi apparatus E) peroxisome
E. Peroxisome
When biological membranes are frozen and then fractured, they tend to break along the middle of the bilayer. The best explanation for this is that ________. A) the integral membrane proteins are not strong enough to hold the bilayer together B) water that is present in the middle of the bilayer freezes and is easily fractured C) hydrophilic interactions between the opposite membrane surfaces are destroyed on freezing D) the carbon—carbon bonds of the phospholipid tails are easily broken E) the hydrophobic interactions that hold the membrane together are weakest at this point
E. The hydrophobic interactions that hold the membrane together are weakest at this point
