Chapter 6 flash cards

B) Passive transport

In order for molecule X to cross the plasma membrane of a cell, it must first bind to an integral membrane protein. The binding of molecule X to the integral membrane protein immediately causes a conformational change to the integral membrane protein, which exposes molecule X to the other side of the membrane where it is then released. What is this an example of? A) Active transport B) Passive transport C) Neutral transport

C) have a glycerol backbone

Phospholipids and triglycerides both A) contain serine or some other organic compound B) have three fatty acids C) have a glycerol backbone D) have a phosphate

E) cotransport.

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

B. Whenever a solute is moved against its electrochemical gradient

46) 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 bilaver membrane D) Whenever oxygen moves through a phospholipid bilayer membrane

C) the phosphate group

A major feature of phospholipids that causes a portion of their structure to be hydrophilic is A) the glycerol backbone B) the unsaturated fatty acid tails C) the phosphate group D) the ester linkages E) the saturated fatty acid tails

A) a transmembrane protein

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

C) ATPase activity must be pumping calcium from the cytosol to the SR against the concentration gradient

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 svstem 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 P; 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) The patient's red blood cells will swell and possibly burst because the blood has become hypotonic compared to the cells.

A patient was involved in a serious accident and lost a large quantity of blood. An inexperienced observer suggests replenishing body fluids by adding distilled water to the blood directly via one of their veins. What would 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. WwW "IBSM. Ws E) The patient's red blood cells will burst because the blood has become hypertonic compared to the cells.

B. A nonpolar lipid molecule that is made amphipathic by the addition of a phosphate.

A phospholipid is a A) nonpolar lipid molecule that is made polar by the addition of a phosphate B) nonpolar lipid molecule that is made amphipathic by the addition of a phosphate C) polar lipid molecule that fully interacts with water D) polar lipid molecule that fully repels water

A) on the side of the membrane that has a lower concentration of the cargo molecule

Carrier proteins release their cargo molecules A) on the side of the membrane that has a lower concentration of the cargo molecule B) on the side of the membrane that has a higher concentration of the cargo molecule C) immediately after a phosphate has been added to the carrier protein D) immediately after a phosphate has been removed from the carrier protein

C. is hypotonic and the salt solution is hypertonic to the cells of the celery stalks

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

A) do not have a polar or charged region

Cooking oil and gasoline (a hydrocarbon) are NOT amphipathic molecules because they A) do not have a polar or charged region B) do not have a nonpolar region C) have hydrophobic and hydrophilic regions D) are highly reduced molecules

C) amphipathic, with at least one hydrophobic region

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

E) facilitated diffusion

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

C) It forms a channel in the membrane.

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.

B) Some lipids will have formed tiny vesicles filled with water.

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.

D) Ions cannot cross planar bilayers.

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 do 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.

A) cotransport proteins

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

B) Certain proteins are unique to each membrane.

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.

D) their electrochemical gradients

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

A) are insoluble in water

Lipids A) are insoluble in water B) are made from glycerol, fatty acids, and nitrogen C) contain less energy than proteins and carbohydrates D) are made by dehydration reactions E) contain sulfur polymers.

D) likely be liquid at room temperature

Lipids that contain a high number of double bonds in their fatty acid chains will A) contain more hydrogens than lipids that contain few double bonds in their fatty acid chains B) have a higher melting temperature than lipids that contain few double bonds in their fatty acid chains C) pack very tightly together at room temperature D) likely be liquid at room temperature E) have more carbons that rotate freely than lipids that contain few double bonds in their fatty acid chains

d. polar heads and nonpolar tails; the polar heads interact with water

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 nompolar tails; the nonpolar tails interact with water. D) Polar heads and nonpolar tails; the polar heads interact with water.

D) It will prevent potassium from being released from the pump.

Preventing the release of the phosphate from the Nat/K+-ATPase will have which of the following effects? A) It will prevent sodium from binding the pump. B) It will prevent sodium from being released from the pump. C) It will prevent potassium from binding the pump. D) It will prevent potassium from being released from the pump.

A) More permeable

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

D) Integral

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 a-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. [Figure adapted from K. Palezewski et al., Science 289 (2000): 739.] 45) Which term best describes the type of membrane protein in the figure? A) Peripheral B) External C) Internal D) Integral

B) Their lipid nature probably allows them to diffuse through the plasma membrane.

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. are not soluble in water

Steroids are considered to be lipids because they A) are essential components of cell membranes B) are not soluble in water C) are made of fatty acids D) are hydrophilic compounds E) contribute to atherosclerosis

A) increasing the percentage of unsaturated phospholipids in the membrane

The membranes of winter wheat remain fluid when it is extremely cold by A) increasing the percentage of unsaturated phospholipids in the membrane B) increasing the percentage of saturated phospholipids in the membrane C) decreasing the number of hydrophobic proteins in the membrane D) cotransport of glucose and hydrogen E) using active transport

A) enables the membranes to stay fluid when cell temperature drops

The presence of cholesterol in the plasma membranes 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) Integral

Use the following information when answering the corresponding question. Rhodopsins are light-sensitive molecules composed of a protein (opsin) and retinal (derivative of vitamin A). Opsin is a membrane protein with several a-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. [Source: O. Beje et al., Science 289 (2000): 1902.7 Refer to the paragraph on rhodopsins. Which of the following best describes rhodopsin? A) Integral B) Peripheral C) External D) Internal

A) It leads to an increase in entropy.

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.

B) The terminal hydroxyl group

What region of the steroid cholesterol is hydrophilic? A) The methyl (-CH3) groups B) The terminal hydroxyl group C) The ring structures D) The long hydrocarbon chain

D) integral and peripheral proteins

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 and peripheral proteins E) cholesterol molecules

E) the hydrophobic interactions that hold the membrane together are weakest at this point.

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

d. spanning the cell membrane, with parts of the protein visible from both the inside and the outside of the cell

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

A) They are amphipathic.

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.

B) Compared to carbohydrates, fatty acid chains have a higher ratio of bonds with high potential energy to bonds with low potential energy.

Which of the following accurately describes a reason why fats store more energy than carbohydrates? A) Fats molecules are always larger than carbohydrate molecules. B) Compared to carbohydrates, fatty acid chains have a higher ratio of bonds with high potential energy to bonds with low potential energy. C) Fatty acid chains have more carbon-carbon bonds than carbohydrates. D) Carbohydrates can be incorporated into polymers through dehydration reactions, while fats cannot form polymers. E) Fats contain more polar groups than carbohydrates.

E) Aquaporins

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

D) A small, nonpolar molecule like oxygen (02)

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 (02)

A) A sodium ion

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 (02)

A) A greater proportion of unsaturated phospholipids

Which of the following factors 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

D) Increasing length of the hydrocarbon chains

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

C) In osmosis, water moves across a membrane from areas of lower solute concentration to areas of higher solute concentration.

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) At low temperatures, cholesterol increases membrane fluidity and permeability by reducing the extent to which phospholipids pack tightly together.

Which of the following is TRUE regarding how cholesterol affects the fluidity and permeability of biological membranes? A) At low temperatures, cholesterol causes phospholipids to pack more tightly together, and therefore, decreases membrane fluidity and permeability. B) At high temperatures, cholesterol increases the spacing between phospholipids and therefore, increases membrane fluidity and permeability. C) At low temperatures, cholesterol increases membrane fluidity and permeability by reducing the extent to which phospholipids pack tightly together. D) At high temperatures, cholesterol decreases membrane fluidity by reducing the extent to which phospholipids pack tightly together!.

B) It exhibits a specificity for a particular type of molecule.

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.

A) A steroid

Which of the following is a large organic molecule that is NOT assembled by polymerization of a few kinds of simple subunits? A) A steroid B) Cellulose C) DNA D) An enzyme E) A contractile protein

E) A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose.

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.

c. Because cholesterol is amphipathic, it fits in between the phospholipids and blocks diffusion through the membrane.

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) Movement of Nations from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid

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 Nations 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

D) passive transport

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

A) Saturated lipids have a higher melting temperature than polyunsaturated lipids.

Which of the following statements is true? A) Saturated lipids have a higher melting temperature than polyunsaturated lipids. B) Unsaturated lipids have fewer carbon-carbon double bonds than saturated lipids. C) Current research suggests that polyunsaturated lipids may induce heart disease. D) Unsaturated lipids pack more tightly together than saturated lipids. E) Saturated lipids are typically liquid at room temperature.

C) Phospholipids and proteins

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

A) COz

Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly? A) COz B) An amino acid C) Glucose D)K+ E) Starch

D) There are only weak hydrophobic interactions in the interior of the membrane.

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.

A) Permeability to glucose will increase.

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 must measure the permeability.

C) The membrane phospholipids of cold-adapted organisms will have more unsaturated hydrocarbon tails.

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.