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 chemical properties.
C) their molecular weight size).
D) where they are found in the body.

Answer 1

B

Question 2

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

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

Answer 2

B

Question 3

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

Answer 3

D

Question 4

Which of the following increases the strength of the hydrophobic interactions in lipid bilayers and thus makes them less permeable to polar molecules?

A) removing cholesterol
B) increasing length of the hydrocarbon chains
C) the presence of double bonds
D) increasing temperature

Question 5

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

Question 6

Steroids are

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

Question 7

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

Question 8

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

Question 9

What do phospholipids and triglycerides have in common?

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

Question 10

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

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

Question 11

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 will have formed planar bilayer membranes.
B) The lipids will have formed tiny vesicles filled with water.
C) The lipids will have completely dissolved in the solution because they are partially polar.
D) The lipids and water will have separated into two distinct layers because the lipids are partially nonpolar.

Question 12

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

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

Question 13

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

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

Question 14

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

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

Question 15

Which of the following is the best explanation for why cholesterol decreases the permeability of biological membranes?

A) Because cholesterol is amphipathic, it forms tiny vesicles that trap solutes.
B) Because cholesterol is amphipathic, it fits in between the phospholipids and blocks diffusion through the membrane.
C) Cholesterol binds to the outside surface of a membrane, thus blocking the movement of solutes.
D) Cholesterol has four rings in its structure that can sequester trap) solutes.

Question 16

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 water somehow blocked the movement of ions across the membrane.
B) The left side would probably also test negative for ions.
C) Ions cannot cross planar bilayers.
D) The experiment failed.

Question 17

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

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

Question 18

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

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

Question 19

What region of a steroid is hydrophilic?

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

Question 20

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

Question 21

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 22

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 stay the same.
C) Permeability to glucose will decrease.
D) Permeability to glucose will increase.

Question 23

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

Question 24

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 stay the same.
C) Permeability to glucose will increase.
D) Permeability to glucose will decrease.

Question 25

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) same permeability
B) less permeable
C) more permeable

Question 26

Which of the following crosses lipid bilayers the fastest?

A) a large, polar molecule like glucose
B) a small, nonpolar molecule like oxygen O₂)
C) a sodium ion
D) a small, polar molecule like water

Question 27

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

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

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) along a nonpolar region of a fi- pleated sheet
C) in the deep interior of hemoglobin
D) in the oxygen binding site of hemoglobin

Question 29

Why do lipid bilayers form spontaneously?

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

Question 30

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

Question 31

Under what circumstances does membrane transport always require energy?

A) whenever a molecule is polar and is moved through a 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 molecules are moved that are too large to pass through the phospholipid bilayer membrane

Question 32

What is the most important factor in explaining why osmosis occurs spontaneously?

A) The process is exothermic.
B) It leads to a decrease in entropy.
C) It leads to an increase in entropy.
D) The process is endothermic.

Question 33

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

Question 34

What is the most important factor in explaining why diffusion occurs spontaneously?

A) The process is endothermic.
B) It leads to a decrease in entropy.
C) The process is exothermic.
D) It leads to an increase in entropy.

Question 35

Which of the following crosses lipid bilayers the slowest?

A) a large, polar molecule like glucose
B) a sodium ion
C) a small, nonpolar molecule like oxygen O₂)
D) a small, polar molecule like water

Question 36

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

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

Question 37

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

Question 38

Why does cholesterol lower membrane permeability?

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

Question 39

Which of the following is not true of osmosis?

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

Question 40

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 only.
C) The inner surfaces of the membrane contained pits and mounds.
D) The exterior surface of the membrane contained pits and mounds.

Question 41

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

Question 42

Use the following information when answering the corresponding questions).
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. [
Which of the following best describes this particular protein?

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

Question 43

Use the following information when answering the corresponding questions).
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. [
Proteorhodopsin consists of a single polypeptide chain. What is the highest level of structure found in this protein?

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

Question 44

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) phospholipids in the cell membrane that are not formed properly
D) movement of chloride ions across cell membranes

Question 45

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) facilitated diffusion
C) phagocytosis
D) exocytosis
E) active transport pumps

Question 46

Where would you most likely find an integral membrane protein?

A) floating freely in the cytoplasm
B) on the inside surface of the cell membrane
C) on the outside surface of the cell membrane
D) spanning the cell membrane, with parts of the protein visible from both the inside and the outside of the cell

Question 47

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

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

Question 48

Based on the figure provided, which of the following experimental treatments would increase the rate of sucrose transport into the cell?

A) adding a substance that makes the membrane more permeable to hydrogen ions
B) decreasing extracellular sucrose concentration
C) decreasing cytoplasmic pH
D) adding an inhibitor that blocks the regeneration of ATP
E) decreasing extracellular pH

Question 49

GLUT- 1 is an example of what?

A) a protein that is toxic to cells because it opens channels in membranes
B) a membrane- bound pump that moves large molecules against a gradient by using ATP
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 50

Which of the following best describes how CFTR functions?

A) It removes electrical charges from solutes.
B) It causes membranes to fuse with one another.
C) It forms a channel in the membrane.
D) It acts by active transport.

Question 51

Integral membrane proteins stay in membranes because of

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

Question 52

In secondary active transport

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

Question 53

Sodium- potassium pumps

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