Deck 6: Lipids, membranes, and the First Cells

Question 1

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

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

Answer 1

C

Question 2

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.

Answer 2

C

Question 3

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)

Answer 3

C

Question 4

You want to view the surface of a particular cell or tissue (group of related cells)at magnifications above 1000x.What tool would you use?

A)scanning electron microscope
B)transmission electron microscope
C)light microscope
D)confocal microscope

Question 5

If you mechanically shook a mixture of amphipathic lipids and water,what would you expect to see when the solution is observed with 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 the solution because they are partially polar.

Question 6

Which characteristic would be expected in the plasma membranes of a plant that can survive winters in Northern Ontario,compared to a plant growing in a warmer region?

A)a higher percentage of saturated fatty acids
B)a higher percentage of unsaturated fatty acids
C)higher levels of cholesterol
D)additional glycerol molecules packed in between fatty acid tails

Question 7

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 8

Phospholipid bilayer membranes are selectively permeable.What does that mean?

A)They allow everything but water to cross.
B)They allow only water to cross.
C)They allow everything nonpolar to cross.
D)They allow some things to cross while restricting others.

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

You want to view a cross section of a particular cell at extremely high magnification.What tool would you use?

A)scanning electron microscope
B)transmission electron microscope
C)light microscope
D)confocal microscope

Question 11

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 12

In marshes and other wet areas where vegetation is rotting,the water surface often has an oily sheen due to insoluble compounds.What are these molecules?

A)nucleic acids
B)proteins
C)lipids
D)carbohydrates

Question 13

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.

Question 14

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 15

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 16

Steroids are

A)a class of lipid with a four-ring structure.
B)a class of transmembrane transport proteins.
C)a portion of all phospholipids.
D)powered by ATP.

Question 17

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 18

Which characteristic would be expected in the plasma membranes of a plant that can survive winters in Northern Ontario,compared to a plant growing in a warmer region?

A)a higher percentage of saturated fatty acids
B)a higher percentage of unsaturated fatty acids
C)higher levels of cholesterol
D)additional glycerol molecules packed in between fatty acid tails

Question 19

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.

Question 20

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 21

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 22

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 23

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 24

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 25

Which of the following is not true of osmosis?

A)It is a special case of diffusion.
B)It is an energy-demanding or "active" process.
C)Water moves from areas of high water concentration to areas of low water concentration.

Question 26

Why does cholesterol lower membrane permeability?

A)It is polar.
B)It fills gaps in membranes and increases hydrophobic interactions.
C)It participates in hydrogen bonding in the membrane interior.
D)It is small relative to most phospholipids.

Question 27

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 28

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 29

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

Question 30

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 31

Suppose some blood cells were in an isotonic solution.What would happen to them?

A)They would shrink.
B)They would expand.
C)They would remain the same size.
D)The outcome is not predictable.

Question 32

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 33

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 34

You make two sucrose solutions,one of 0.5M and one of 2M and go out for lunch.When you return,you realize that you forgot to label the beakers! You remake the solutions,but give the undergrads in your lab an experiment to determine which beaker holds which solution.They fill two balloons,which are semi-permeable to water,but not to sucrose,with a 0.75M sucrose solution.One balloon is then placed in each of the unknown sucrose solution beakers.After several hours,they observe that the balloon in beaker 1 has swelled,while the balloon in beaker 2 has shrivelled.This indicates that beaker one contained the ________ sucrose solution,while beaker 2 contained the ________ sucrose solution.

A)0)5M,2M
B)2M,0,5M
C)unable to determine given the information provided.

Question 35

You make two sucrose solutions,one 0.5M and one of 2M and go out for lunch.When you return,you realize that you forgot to label the beakers! You remake the solutions,but give the undergrads in your lab an experiment to determine which beaker holds which solution.They fill two balloons,which are semi-permeable to water,but not to sucrose,with a 0.75M sucrose solution.One balloon is then placed in each of the unknown sucrose solution beakers.After several hours,they observe that the balloon in beaker 1 has swelled,while the balloon in beaker 2 has shriveled.This indicates that the solution in beaker 1 was ________ relative to the solution in the balloon,while beaker 2's solution was ________ relative to the solution in the balloon.

A)hypertonic,hypotonic
B)hypotonic,hypertonic
C)hypotonic,isotonic
D)hypertonic,isotonic

Question 36

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 37

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 38

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 39

The cell membrane is often referred to as asymmetrical or "mosaic".This means that

A)both layers of the phospholipid bilayer are not identical in terms of protein type or number and phospholipid type.
B)only certain substances can pass through the phospholipid bilayer freely,while others require the help of membrane proteins.
C)the phospholipids of the membrane can flip-flop such that phospholipids from the inner layer are exchanged with those from the outer layer.

Question 40

You have a planar bilayer at a relatively warm temperature.After testing the permeability of this membrane to glucose,you increase the quantity of cholesterol in the bilayer.What will happen?

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 41

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 42

Which of the following best describes this particular protein?

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

Question 43

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

What is the name of the currently accepted model of membrane structure,and where does it place membrane proteins?

A)fluid-mosaic;on the surfaces of the membrane only
B)fluid-mosaic;embedded within the membrane and on the surfaces of the membrane
C)sandwich;on the outside and inside surfaces of the membrane only
D)sandwich;embedded within the membrane and on the surfaces of the membrane

Question 45

Which of the following best describes how gramicidin functions?

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 46

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 47

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 48

In secondary active transport

A)two molecules are simultaneously moved across the cell membrane down their concentration gradients with the help of transport proteins.
B)water is moved across the cell membrane based on solute concentration.
C)a gradient is set up by a pump which then provides the potential energy to move a different molecule against its concentration gradient.
D)Molecules are able to cross the plasma membrane unassisted with the help of ATP.

Question 49

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 50

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 51

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 52

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

Question 53

Which of the following is not a difference between passive facilitated transport and active transport?

A)Active transport requires energy input in the form of ATP,while facilitated transport does not.
B)Active transport moves substances against their concentration gradient,while facilitated transport moves substances down their concentrations gradient.
C)Active transport requires a membrane protein to move molecules across the plasma membrane,while facilitated transport does not.
D)Active transport and facilitated transport both play a role in maintaining proper concentrations of substances in the intra- and extracellular environments.

Question 54

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 because it opens 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