Deck 6: Lipids, membranes, and the First Cells

Question 1

What most distinguishes lipids from other biomolecules is _____.

A)that only lipids contain hydrogen atoms
B)their molecular weight (size)
C)their chemical properties
D)where they are found in the body

Answer 1

C

Question 2

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.

Answer 2

C

Question 3

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

Answer 3

D

Question 4

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 graphs below best represents the data you expect if your null hypothesis is correct?

A)
B)
C)
D)

Question 5

How do phospholipids interact with water molecules?

A)The polar heads avoid water;the nonpolar tails attract water (because water is polar and opposites attract).
B)Phospholipids don't interact with water because water is polar and lipids are nonpolar.
C)The polar heads interact with water;the nonpolar tails do not.
D)Phospholipids dissolve in water.

Question 6

What region of a steroid is hydrophilic?

A)the methyl (-CH₃)groups
B)the terminal hydroxyl group
C)the ring structures
D)the long hydrocarbon chain

Question 7

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 graphs below best represents the data you expect?

A)
B)
C)
D)

Question 8

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.

Question 9

Which of the following is the best explanation for why vegetable oil is a liquid at room temperature while animal fats are solid?

A)Vegetable oil has more double bonds than animal fats.
B)Vegetable oil has fewer double bonds than animal fats.
C)Animal fats have no amphipathic character.
D)Vegetable oil has longer fatty-acid tails than animal fats have.

Question 10

The term phospholipid can best be described by which of the following?

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

Question 11

Phospholipids can form all of the following structures in water except which one?

A)micelles
B)bilayers
C)monolayers
D)vesicles

Question 12

Which aspect of phospholipids is most important to the formation of bilayers?

A)They are amphipathic.
B)Their size is large,relative to cholesterol.
C)Their size is small,relative to fats.
D)Their hydrocarbon tails can consist of fatty acids or isoprene subunits.

Question 13

Which of the following phospholipid membranes would be most permeable to glycerol?

A)one with long and saturated fatty-acid tails
B)one with long and unsaturated tails
C)one with short and saturated tails
D)one with short and unsaturated tails

Question 14

Which of the following substances would most likely require a protein to facilitate its diffusion across a cell membrane?

A)water
B)glycerol
C)fatty acid
D)oxygen gas (O₂)

Question 15

Steroids such as cholesterol are an important component of animal cell membranes but do not actually form the membrane.Why?

A)The ring structure of steroids is too bulky to form a membrane.
B)Lipids that form membranes are amphipathic with a polar region and a nonpolar region.
C)Steroids cannot interact with other molecules,which is required to form a cell membrane.
D)Steroids are too permeable to charged molecules to form a cell membrane.

Question 16

If you mechanically shook a mixture of amphipathic lipids 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)The lipids will have formed tiny vesicles filled with water.
C)The lipids will have formed planar bilayer membranes.
D)The lipids will have completely dissolved in solution because they are partially polar.

Question 17

Lipids that form membranes have what kind of structure?

A)completely nonpolar,because they are lipids
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

Question 18

What type of functional group results when the alcohol group on glycerol reacts with the carboxylic acid group on a fatty acid?

A)ester
B)hydrocarbon
C)peptide bond
D)glycosidic bond

Question 19

What do phospholipids and triglycerides have in common?

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

Question 20

Cooking oil and gasoline (a hydrocarbon)are not amphipathic molecules.Why?

A)They do not have a polar or charged region.
B)They do not have a hydrophobic region.
C)They are highly reduced molecules.
D)They spontaneously form micelles or liposomes in solution.

Question 21

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 nature 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.

Question 22

Why do lipid bilayers form spontaneously?

A)The process is endergonic.
B)The process is exergonic.
C)The process leads to a huge decrease in entropy and no change in potential energy.
D)The process is endothermic.

Question 23

To determine if membrane proteins affect membrane permeability,you could isolate the proteins from the lipid components of the membrane by using detergents.Then you could separate the individual proteins and test each of them in a planar bilayer.What technique could you use to separate the proteins from one another after they have been isolated from the membrane?

A)gel electrophoresis
B)freeze-fracture electron microscopy
C)diffusion
D)amino acid analysis

Question 24

Under what circumstances does membrane transport always require energy?

A)whenever molecules are moved that are too large to pass through the phospholipid bilayer membrane
B)whenever a solute needs to be moved from low concentration to high concentration through a phospholipid bilayer membrane
C)whenever a solute is charged,such as an ion,and is moved through a phospholipid bilayer membrane
D)whenever a molecule is polar and is moved through a phospholipid bilayer membrane

Question 25

Which of the following is true of osmosis?

A)It only takes place in red blood cells.
B)It is an energy-demanding or "active" process.
C)Water moves from areas of low water concentration to areas of high water concentration.

Question 26

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

Question 27

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.

Question 28

Valine,a nonpolar amino acid,shows up in the wrong place in the hemoglobin of sickle-cell anemia,causing the disease.This is due to a genetic mutation.The result of this mutation is that hemoglobin molecules-which transport oxygen in red blood cells-stick together,causing the red blood cells to become distorted,but without having any significant effect on oxygen binding.Based on what you know about protein structure and the polarity of amino acids,predict where the mutated valine would most likely be found.

A)on the surface of hemoglobin
B)in the deep interior of hemoglobin
C)in the oxygen binding site of hemoglobin
D)along a nonpolar region of a β-pleated sheet

Question 29

What preserves the structural integrity of phospholipid bilayers?

A)Peptide bonds form between the phosphate groups of the phosopholipids.
B)Sugars associated with the cell membrane covalently cross-link.
C)hydrophobic and hydrophilic interactions between nearby phospholipids
D)van der Waals interactions between the glycerol molecule and fatty acids of a single phospholipid

Question 30

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)

Question 31

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.

Question 32

What will happen to a red blood cell (RBC),which has an internal ion concentration of about 0.9 percent,if it is placed into a beaker of pure water?

A)nothing
B)The cell would shrink because the water in the beaker is hypotonic relative to the cytoplasm of the RBC.
C)The cell would shrink because the water in the beaker is hypertonic relative to the cytoplasm of the RBC.
D)The cell would swell because the water in the beaker is hypotonic relative to the cytoplasm of the RBC.

Question 33

What is the most important factor in explaining why diffusion 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.

Question 34

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)

Question 35

Which of the following functions do lipids provide in a cell?

A)structural
B)cell identification
C)information storage
D)neither structural,cell identification,nor information storage

Question 36

You place yeast cells in a glucose solution and plot the rate of glucose uptake.You see an increase in glucose uptake over time (that is,the longer the yeast are in the sugar solution,the faster they can take sugar into the cell).The most likely explanation for this is the cell membrane is becoming more permeable because _____.

A)the yeast is inserting more cholesterol into the membrane
B)the difference in glucose concentration between the inside of the cell and outside of the cell is increasing
C)the difference in glucose concentration between the inside of the cell and outside of the cell is decreasing
D)the yeast is inserting more glucose protein transporters into its membrane

Question 37

Integral membrane proteins stay in membranes because of _____.

A)osmotic pressure from proteins outside the cell
B)diffusion of proteins from the cytoplasm to the membrane
C)the locations of their polar and nonpolar amino acids
D)their small size,which does not allow them to pass through the membrane

Question 38

Which of the following observations made with freeze-fracture electron microscopy provides evidence for the fluid-mosaic model of membrane structure?

A)The middle of the membrane viewed under the electron microscope was smooth and regular.
B)The exterior surface of the membrane contained pits and mounds.
C)The inner surfaces of the membrane contained pits and mounds.
D)The exterior surface of the membrane contained pits only.

Question 39

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)You can't predict the outcome.You simply have to make the measurement.
B)Permeability to glucose will increase.
C)Permeability to glucose will decrease.
D)Permeability to glucose will stay the same.

Question 40

The text states that ribonucleotides can diffuse through some types of liposomes.It's 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

Question 41

Use the following information when answering the corresponding question(s).
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.[Source: O.Beje et al. ,Science 289 (2000): 1902.]
Refer to the paragraph on Rhodopsins.Which of the following best describes this particular protein?

A)integral
B)peripheral
C)external
D)internal

Question 42

Use the following information when answering the corresponding question(s).
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.[Source: O.Beje et al. ,Science 289 (2000): 1902.]
GLUT-1 is an example of what?

A)a membrane-bound pump that moves large molecules against a gradient by using ATP
B)a protein that is toxic to cells by opening channels in membranes
C)a recognition protein that identifies cells as belonging to the body
D)a transport protein that facilitates diffusion of a large molecule across cell membranes

Question 43

Use the following information when answering the corresponding question(s).
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.[Source: O.Beje et al. ,Science 289 (2000): 1902.]
Sodium-potassium pumps _____.

A)move three potassium ions and two sodium ions while producing an ATP for each cycle
B)move two potassium ions and three sodium ions while consuming an ATP for each cycle
C)produce ATP for cells while making the outside of cell membranes negatively charged
D)use ATP molecules to move protons to the inner side of cell membranes

Question 44

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.

Question 45

Use the following information when answering the corresponding question(s).
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.[Source: O.Beje et al. ,Science 289 (2000): 1902.]
Cystic fibrosis (CF)is a membrane-transport disease that is caused by an allele found primarily in Caucasian populations.What mechanism fails in CF patients?

A)production of ATP
B)movement of sodium and potassium across cell membranes
C)movement of chloride ions across cell membranes
D)phospholipids in the cell membrane that are not formed properly

Question 46

Use the following information when answering the corresponding question(s).
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.[Source: O.Beje et al. ,Science 289 (2000): 1902.]
Proteorhodopsin consists of a single polypeptide chain.What is the highest level of structure found in this protein?

A)primary
B)secondary
C)tertiary
D)quaternary

Question 47

Which of the following means of transport would most likely be used for moving a medium-sized molecule (like a monosaccharide or an amino acid)from a low concentration on the outside of a cell to a high concentration on the inside of a cell?

A)facilitated diffusion through an ion channel protein
B)facilitated diffusion through a transporter protein
C)active transport through a "pump" protein
D)passive transport