Deck 3: Membrane Physiology

Question 1

All cells (not just animal cells) have

A) mitochondria.
B) a cell membrane.
C) a cell wall.
D) a nucleus.
E) microtubules.

Answer 1

a cell membrane.

Question 2

Phospholipids are able to form bilayer membranes in aqueous environments because

A) they have hydrophobic heads and hydrophilic tails.
B) they have polar heads and nonpolar tails.
C) they have polar tails and nonpolar heads.
D) the phospho-portion can form phosphodiester bonds between adjacent phospholipids.
E) two of these.

Answer 2

they have polar heads and nonpolar tails.

Question 3

The lipid bilayer is held together mainly by

A) covalent bonding between membrane lipids.
B) hydrogen-bonding between the phospholipids' tails.
C) repulsion between the phospholipids' tails and water.
D) covalent bonding between the ends of phospholipids tails in opposite layers.
E) hydrogen-bonding between the head groups of the phospholipids.

Answer 3

repulsion between the phospholipids' tails and water.

Question 4

Cell membranes have a ____ structure with the polar head groups of the phospholipids facing toward the aqueous environment and the ____ facing toward the interior of the membrane.

A) bilayer, hydrophilic tails
B) bilayer, hydrophobic tails
C) micellar, hydrophilic tails
D) liposomal, hydrophilic tails
E) liposomal, hydrophobic tails

Question 5

Cholesterol is a membrane lipid that

A) reduces the permeability of gill membranes to water.
B) affects the activity of membrane proteins.
C) regulates membrane fluidity and stability.
D) two of these.
E) all of these.

Question 6

Which of the following statements regarding lipid membranes is true?

A) Phospholipids will spontaneously form liposomes in nonpolar solvents.
B) A solution of pure fatty acids forms a lipid bilayer in a polar solvent.
C) Membrane lipids move laterally within their own layer.
D) Membrane lipids frequently move between one layer of the bilayer and the other.
E) The preferred form of a lipid bilayer in water is a flat sheet with exposed edges.

Question 7

Which of the following statements regarding the fatty acid tails of phospholipids is FALSE?

A) Phospholipids with unsaturated tails make the bilayer more fluid because the tails contain fewer hydrogens and thus form fewer hydrogen bonds with each other.
B) Saturated phospholipids' tails pack more tightly against each other than do unsaturated tails.
C) Most membrane phospholipids have one fully saturated tail.
D) Phospholipid tails in a membrane can interact with each other via van der Waals interactions.
E) Fatty acid tails vary in length.

Question 8

Which of the following animals would you expect to have the most unsaturated fatty acyl chains in the plasma membranes of its cells?

A) arctic fish
B) penguins
C) polar bears
D) tropical fish
E) pelicans

Question 9

Membrane proteins are found

A) as distinct layers with one layer facing the extracellular fluid and the other facing the intracellular fluid.
B) both embedded in and associated with the lipid bilayer of the plasma membrane.
C) associated with the lipid bilayer of the plasma membrane, but not actually embedded in it.
D) only in the plasma membrane, and not in other cellular membranes.
E) none of these.

Question 10

Which of the following statements about the plasma membrane is true?

A) The plasma membrane is symmetrical (on average) around the plane between the inner and outer halves.
B) The carbohydrate portion of glycoproteins is only found on the part of the protein facing the cytoplasm.
C) The carbohydrate portion of glycoproteins is only found on the part of the protein facing the extracellular fluid.
D) The carbohydrate portion of glycoproteins is found on both the extracellular facing and intracellular facing part of the protein.
E) There are no glycoproteins in the plasma membrane.

Question 11

Which of the following statements about the lipid bilayer portion of the plasma membrane is FALSE?

A) Some membrane phospholipids form transmembrane channels that allow ion movement.
B) The lipid bilayer defines the boundaries of the cell.
C) The lipid bilayer forms a permeability barrier to polar and charged substances.
D) The lipid bilayer confers fluidity to the plasma membrane.
E) All of the above statements are true.

Question 12

Ion channels

A) can exist in open or closed states.
B) are typically selective with respect to the types of substances that pass through them.
C) can selectively repel particular ions.
D) all of these.
E) none of these.

Question 13

From a structural standpoint, integral membrane proteins are most similar to which membrane lipids?

A) cholesterol
B) phospholipids
C) neutral lipids
D) polyunsaturated fatty acids.
E) none of these.

Question 14

Which of the following pairs have NO relationship?

A) hydrostatic pressure and osmosis.
B) osmotic pressure and osmosis.
C) osmotic pressure and colligative properties of solutes.
D) all of these pairs have a relationship.
E) none of these pairs has a relationship.

Question 15

A semipermeable membrane encloses a solution of 10 mM NaCl and 5 mM KCl. This "cell" is placed into a solution of 6 mM CaCl₂ and 6 mM NaCl.

A) The "cell" will be hypertonic to the surrounding solution.
B) The "cell" will be isotonic to the surrounding solution.
C) The "cell will be hypotonic to the surrounding solution.
D) The "cell" has a lower hydrostatic pressure than the surrounding solution.
E) Not enough information is provided to answer the question.

Question 16

Molecules that can cross a membrane unassisted due so either by

A) carrier mediated transport or facilitated diffusion.
B) passive diffusion or active transport.
C) conduction or passive transport.
D) facilitated diffusion or active transport.
E) none of these.

Question 17

Which of the following does NOT directly affect the rate of diffusion of a substance across a membrane?

A) concentration gradient
B) cellular volume
C) permeability of the membrane to the diffusing substance
D) surface area across which diffusion is taking place
E) molecular weight of the diffusing substance

Question 18

Osmosis is the movement of water

A) using a carrier-mediated transport mechanism.
B) down a solute's concentration gradient.
C) down its own concentration gradient.
D) across a membrane irrespective of concentration gradients.
E) across a membrane down its own concentration gradient.

Question 19

Osmotic pressure is

A) a measure of the concentration of solvent in a solution.
B) equal to the hydrostatic pressure required to oppose the movement of water into a solution.
C) low in a solution with a high solute concentration.
D) dependent upon the lipid composition of the membrane.
E) two of these are correct.

Question 20

Which of the following statements is true?

A) Tonicity refers to the effect of penetrating solutes on cell volume.
B) A one molal solution contains 1 mole of solute per liter of solution.
C) To accommodate larger molecules, membrane channels have an average diameter of 1 - 1.5 nanometers.
D) Carrier proteins span the membrane and can undergo shape changes.
E) Aquaporins regulate solute movement across membranes.

Question 21

In a lab experiment with isolated lung cells you observe a linear uptake in choline from the extracellular medium by the cells until the extracellular concentration of choline reaches 200 nM. At this concentration the curve levels off and the same rate of uptake is seen at 200 and 225 nM extracellular choline. What has happened that can explain this observation?

A) Cellular and extracellular choline concentrations are at equilibrium.
B) The transporters for choline saturate at 200 nM.
C) At choline concentrations of 200 nM and above, the osmotic pressure of the cytoplasm prevents additional choline from entering the cell.
D) The cell cannot synthesis enough ATP to keep up with the energy demand of the carrier.
E) None of these.

Question 22

A scientist measuring the rate of uptake of radiolabeled alanine by cultured cells finds that rates are faster when the experiments are carried out in a buffered, balanced salts solution than when the experiments are carried out in a complete (containing all nutrients required for survival and growth) medium. The most likely explanation for this observation is

A) the concentration gradient for alanine is steeper in the former case than the latter.
B) the crenation (shrinkage of cells) in the salts solution increases the surface area-to-volume ratio for the cells increasing the rate of diffusion.
C) the absence of amino acids in the balanced salts solution decreases the abundance of molecules competing for transport, and therefore increases the apparent transport rate.
D) the temperature of the balanced salt solution is higher, so rates of transport are greater.
E) no response provides a valid answer.

Question 23

Which of the following pairs have NO relationship?

A) Secondary active transport and cotransport carriers.
B) Symporters and cotransport carriers.
C) Na⁺-K⁺ pump and ouabain.
D) Caveolae and cell transport.
E) Osmosis and carrier mediated transport.

Question 24

Which of the following is a NOT direct function of the Na⁺-K⁺ pump?

A) development of a Na⁺ gradient across the cell membrane
B) development of a K⁺ gradient across the cell membrane
C) regulation of cellular pH
D) cell volume regulation
E) all of these are direct functions of this pump.

Question 25

Nursing babies obtain some immunity by intestinal absorption of antibodies found in their mother's milk. This process requires the movement of intact antibodies from the lumen of the intestine into the blood. This process involves a combination of

A) endocytosis.
B) exocytosis.
C) cotransport carriers.
D) endocytosis and cotransport carriers.
E) endocytosis and exocytosis.

Question 26

The term potocytosis refers to

A) the uptake of substances through the activity of caveolae.
B) the specific uptake of tetrahydrocannabinol by facilitated diffusion.
C) the uptake of solid substances involving the formation of pseudopods.
D) the uptake of liquids through cellular drinking.

Question 27

Which of the following would disqualify a chemical messenger from being considered a paracrine signal?

A) It is an organic molecule.
B) It is not transported in the blood.
C) It affects the cell that released it.
D) Once released, it is distributed to its target(s) by simple diffusion.
E) It is released as a specific response to a signal.

Question 28

The affect a chemical messenger elicits in a cell is determined primarily by the identity of

A) the chemical messenger.
B) the receptor for the chemical messenger.
C) the second messengers present in the cell.
D) the cell.
E) the organism.

Question 29

Which of the following sequences best represents the order of events in the cAMP second messenger pathway?

A) cAMP $\rightarrow$ receptor $\rightarrow$ G-protein activation $\rightarrow$ PKA $\rightarrow$ phosphoproteins
B) receptor $\rightarrow$ G-protein activation $\rightarrow$ AC $\rightarrow$ cAMP $\rightarrow$ PKA $\rightarrow$ phosphoproteins
C) AC $\rightarrow$ decreased temperature $\rightarrow$ phospholipid-breakdown $\rightarrow$ cAMP $\rightarrow$ PKA $\rightarrow$ phosphoproteins
D) G-protein activation $\rightarrow$ GDP $\rightarrow$ cGMP $\rightarrow$ cAMP $\rightarrow$ PKA $\rightarrow$ phosphoproteins
E) None of the above.

Question 30

One advantage of signaling pathways involving the generation of second messengers has compared to a signaling pathway that utilizes the influx of ions is

A) the former are much faster in terms of generating cellular responses to first messengers.
B) the former are slower in terms of generating cellular responses, allowing cells to be more circumspect in their response to chemical signals.
C) the former require less first messenger to elicit a response, since they allow for signal amplification.
D) the former require more first messenger to elicit a response, allowing for more rapid termination of the signaling event.
E) none of these.

Question 31

The internal (intracellular) receptor for steroid hormones acts as a transcription factor. Therefore, the cellular response to a steroid would be expected to include

A) an increase in mRNA produced from specific genes.
B) an increase in protein production, representing specific gene products.
C) both of these.
D) neither of these.

Question 32

Two chambers containing aqueous solutions are separated by a membrane. Chamber 1 contains 10 mM Na⁺ while chamber 2 contains 1 mM Na⁺. The membrane potential (1 relative to 2) in this scenario

A) is greater than 0 mV.
B) is equal to 0 mV.
C) is less than 0 mV.
D) cannot be determined based on the information given.

Question 33

Potassium efflux from most cells is driven by

A) the concentration gradient for potassium.
B) the charge gradient across the membrane.
C) the concentration gradient for sodium.
D) the action of the Na⁺-K⁺ pump.
E) none of these.

Question 34

Which of the following statements is FALSE?

A) Hormones are long distance signaling molecules.
B) Nanotubes allow the movement of organelles between adjacent cells.
C) Cytokines may act as small, long distance signaling molecules.
D) Paracrine signaling molecules are one type of chemical communication between
Organisms.
E) Steroids are hydrophobic molecules derived from cholesterol.

Question 35

Two chambers are separated by a cation-permeable membrane. The first chamber contains 10 mM NaCl and 1 mM KCl, and the second chamber contains 10 mM KCl and 1 mM NaCl. At equilibrium, the membrane potential (with chamber 1 relative to chamber 2) is

A) greater than 0 mV.
B) equal to 0 mV.
C) less than 0 mV.
D) unable to be determined without knowing the temperature.

Question 36

For most cells, the membrane potential is closer to the E_k+ (-90 mV) than for E_Na+ (+ 60 mV). This is because

A) E_K+ <<<< E_Na+, and systems tend toward lower energy states.
B) cells like potassium better than sodium, so they work to maintain potassium closer to its equilibrium distribution.
C) cell membranes are equally permeable to Na⁺ and Cl^-, so every time a Na⁺ comes in, its depolarizing effect is negated by a Cl^- ion.
D) cell membranes are more permeable to K⁺ than Na⁺, so there are a greater number of pathways available for K⁺ to move towards its equilibrium distribution than are available for Na⁺ to do the same.
E) none of these.

Question 37

Signaling molecules are divided into categories based upon their chemical structure. Which of the following is NOT a chemical structure category for signaling molecules?

A) retinoids
B) gases
C) pyrimidines
D) amines
E) peptides

Question 38

The equilibrium potential for most neurons is around -70mV. The maintenance of this potential is an example of

A) equilibrium.
B) homeostasis.
C) steady state.
D) both equilibrium and homeostasis.
E) both homeostasis and steady state.

Question 39

Glycoproteins are found only on the outer surface of membranes.

Question 40

Net diffusion leads to the establishment of an equilibrium, but not a steady state.

Question 41

The electrochemical gradient is the charge difference that occurs across the plasma
membrane.

Question 42

A solution that is hypertonic is also hyperosmotic.

Question 43

Secondary active transport relies on an ion concentration gradient.

Question 44

Histamine is an example of an autocrine signaling molecule.

Question 45

Nanotubes are one example of intercellular communication in mammals.

Question 46

Neurosecretory neurons are adapted for hormone production and therefore do not
conduct.

Question 47

The G-protein signaling pathway begins with the binding of the first messenger to
adenylyl cyclase.

Question 48

The term membrane potential means that the separated ions have the ability to do work.

Question 49

Match each sentence with the most appropriate choice:

-Caveloae

A) Potocytosis
B) secretion
C) ATP
D) PIP2
E) cAMP
F) DAG
G) Ca2+
H) equilibrium potential
I) cell volume
J) receptor

Question 50

Match each sentence with the most appropriate choice:

-Exocytosis

A) Potocytosis
B) secretion
C) ATP
D) PIP3
E) cAMP
F) DAG
G) Ca2+
H) equilibrium potential
I) cell volume
J) receptor

Question 51

Match each sentence with the most appropriate choice:

-AC

A) Potocytosis
B) secretion
C) ATP
D) PIP4
E) cAMP
F) DAG
G) Ca2+
H) equilibrium potential
I) cell volume
J) receptor

Question 52

Match each sentence with the most appropriate choice:

-PLC

A) Potocytosis
B) secretion
C) ATP
D) PIP5
E) cAMP
F) DAG
G) Ca2+
H) equilibrium potential
I) cell volume
J) receptor

Question 53

Match each sentence with the most appropriate choice:

-PDE

A) Potocytosis
B) secretion
C) ATP
D) PIP6
E) cAMP
F) DAG
G) Ca2+
H) equilibrium potential
I) cell volume
J) receptor

Question 54

Match each sentence with the most appropriate choice:

-PKC

A) Potocytosis
B) secretion
C) ATP
D) PIP7
E) cAMP
F) DAG
G) Ca2+
H) equilibrium potential
I) cell volume
J) receptor

Question 55

Match each sentence with the most appropriate choice:

-Calmodulin

A) Potocytosis
B) secretion
C) ATP
D) PIP8
E) cAMP
F) DAG
G) Ca2+
H) equilibrium potential
I) cell volume
J) receptor

Question 56

Match each sentence with the most appropriate choice:

-Nernst equation

A) Potocytosis
B) secretion
C) ATP
D) PIP9
E) cAMP
F) DAG
G) Ca2+
H) equilibrium potential
I) cell volume
J) receptor

Question 57

Match each sentence with the most appropriate choice:

-Hydrostatic pressure

A) Potocytosis
B) secretion
C) ATP
D) PIP10
E) cAMP
F) DAG
G) Ca2+
H) equilibrium potential
I) cell volume
J) receptor

Question 58

Match each sentence with the most appropriate choice:

-Agonist

A) Potocytosis
B) secretion
C) ATP
D) PIP11
E) cAMP
F) DAG
G) Ca2+
H) equilibrium potential
I) cell volume
J) receptor

Question 59

Assuming that the Na⁺-K⁺ pumps are located on the basolateral membrane (the side away from the environment) of salmon gill epithelium, explain how increasing the number of pumps helps the animal adjust to life in the sea.

Question 60

Describe an experiment to demonstrate that lipid composition and structure affect plasma membrane fluidity and stability.

Question 61

Why is the chemical composition of a cell's cytoplasm so critical to its survival in the body?

Question 62

Describe an experiment that would enable you to test whether a specific ion was
important in determining the membrane potential for a specific cell.

Question 63

Explain why a large increase in extracellular potassium is more life-threatening than a
similar increase in extracellular sodium.