Plasma Membrane

Question 1

1. The plasma membrane functions as a
   a. selective barrier to the passage of molecules.
   b. sensor through which the cell receives signals from the environment.
   c. site for uptake of macromolecules into the cell.
   d. site for RNA synthesis.
   e. All of the above

Answer 1

a. selective barrier to the passage of molecules.

Question 2

2. The plasma membrane barrier to passive diffusion is primarily a function of the
membrane’s
a. phospholipids.
b. cholesterol.
c. proteins.
d. glycoproteins.
e. All of the above

Answer 2

a. phospholipids.

Question 3

3. Mammalian erythrocytes (red blood cells) are particularly useful for studies of the
   plasma membrane because
   a. they have few peripheral proteins.
   b. they have only one membrane, the plasma membrane.
   c. their plasma membrane is not associated with a cytoskeleton.
   d. their plasma membrane contains no cholesterol.
   e. All of the above

Answer 3

b. they have only one membrane, the plasma membrane.

Question 4

5. Plasma membrane phospholipids are
   a. located mostly in the outer leaflet of the bilayer.
   b. located mostly in the inner leaflet of the bilayer.
   c. symmetrically distributed between the two membrane halves.
   d. asymmetrically distributed between the two membrane halves.
   e. mostly symmetrically distributed between the two membrane halves, but
   phosphatidylinositol is only in the inner leaflet

Answer 4

d. asymmetrically distributed between the two membrane halves.

Question 5

6. Cholesterol is present in the membranes of all
   a. cells.
   b. eukaryotic cells.
   c. animal cells.
   d. plant cells.
   e. animal and plant cells.

Answer 5

c. animal cells.

Question 6

7. Plasma membrane glycolipids are found
   a. exclusively in the inner leaflet.
   b. exclusively in the outer leaflet.
   c. equally distributed between the inner and outer leaflets.
   d. only on the basal surface of epithelia.
   e. None of the above

Answer 6

b. exclusively in the outer leaflet.

Question 7

8. Clusters of sphingolipids, cholesterol, and membrane proteins that move together
   laterally in the plane of the plasma membrane are called lipid
   a. boats.
   b. barrels.
   c. rafts.
   d. barges.
   e. patches

Answer 7

c. rafts.

Question 8

10. The two erythrocyte proteins, glycophorin and band 3, are examples of
    a. peripheral proteins.
    b. transmembrane proteins.
    c. cytoskeletal proteins.
    d. β-barrel proteins.
    e. membrane proteins of known function

Answer 8

b. transmembrane proteins.

Question 9

11. Porins form membrane channels whose structure is formed by a
    a. ring of α helices.
    b. barrel of β sheets.
    c. hole down the center of an α helix.
    d. mix of α helices and β sheets.
    e. None of the above

Answer 9

b. barrel of β sheets.

Question 10

12. Which of the following bacterial membrane contains porins?
    a. The outer membrane of E. coli
    b. The inner (plasma) membrane
    c. The outer mitochondrial membrane
    d. The mesosomal membrane
    e. The thylakoid membrane

Answer 10

a. The outer membrane of E. coli

Question 11

13. Above the temperature at which lipids are fluid, membrane proteins are able to move
    a. from inner to outer surfaces of a membrane.
    b. laterally in the plane of a membrane.
    c. from apical to basal surfaces of intestinal epithelial cells.
    d. only if attached to microtubules or microfilaments.
    e. a, b, and c

Answer 11

b. laterally in the plane of a membrane.

Question 12

14. Specific recognition between cell types such as leukocytes and endothelial cells of
    blood vessels is mediated by cell-surface glycoproteins called
    a. lectins.
    b. fibronectins.
    c. nexins.
    d. selectins.
    e. Thy 1 and 2

Answer 12

d. selectins.

Question 13

15. Molecules that diffuse passively across the plasma membrane most rapidly are
    a. small.
    b. hydrophobic.
    c. small and hydrophobic.
    d. small and hydrophilic.
    e. charged

Answer 13

b. hydrophobic.

Question 14

16. Facilitated diffusion differs from passive diffusion in that facilitated diffusion is
    a. mediated only by a protein channel.
    b. mediated only by a protein carrier.
    c. unidirectional.
    d. mediated by a protein carrier or channel.
    e. against the concentration gradient.

Answer 14

d. mediated by a protein carrier or channel.

Question 15

17. The glucose-facilitated diffusion transporter can transport glucose
    a. into the cell only.
    b. out of the cell only.
    c. into or out of the cell.
    d. only in the presence of ATP.
    e. only in the presence of a Na+ gradient.

Answer 15

a. into the cell only.

Question 16

18. Channels that open in response to neurotransmitters or other signal molecules are
called \_\_\_\_\_\_\_ channels.
a. voltage-gated
b. ligand-gated
c. signal-gated
d. ion
e. transporter

Answer 16

b. ligand-gated

Question 17

19. Which of the following has the fastest rate of transport?
    a. Channel-mediated diffusion
    b. Facilitated diffusion
    c. Active transport
    d. Facilitated diffusion and active transport are equally fast.
    e. All of the above are equally fast.

Answer 17

a. Channel-mediated diffusion

Question 18

20. Which of the following describes the relative concentrations of ions in a typical
    mammalian cell?
    a. Na+ and Cl– higher inside, K+ higher outside
    b. Na+ higher inside, K+ and Cl– higher outside
    c. K+ higher inside, Na+ and Cl– higher outside
    d. K+ and Cl– higher inside, Na+ higher outside
    e. None of the above

Answer 18

c. K+ higher inside, Na+ and Cl– higher outside

Question 19

21. The resting potential of a typical eukaryotic cell is _______ mV.
    a. 0
    b. –60
    c. +60
    d. –100
    e. +100

Answer 19

b. –60

Question 20

23. The flow of which of the following ions makes the largest contribution to the resting
potential?
a. K+
b. Na+
c. Cl–
d. H+
e. Ca2+

Answer 20

a. K+

Question 21

24. What would be the resting potential across an artificial membrane if all charged
    molecules on both sides were equally permeable?
    a. 1 mV
    b. –60 mV
    c. +60 mV
    d. 0 mV
    e. –1 mV

Answer 21

d. 0 mV

Question 22

25. Voltage-sensitive K+ channels are one-thousand times more permeable to K+ than to
    Na+ because
    a. K+ ions are smaller than Na+ ions.
    b. K+ ions have a lower charge density than Na+ ions.
    c. a selectivity filter removes the water molecules from K+ ions but not from Na+ ions.
    d. K+ ions have a higher charge density than Na+ ions.
    e. K+ ions are more concentrated inside the cell than outside the cell.

Answer 22

c. a selectivity filter removes the water molecules from K+ ions but not from Na+ ions.

Question 23

26. Active transport is transport
    a. in an energetically unfavorable direction always driven by hydrolysis of ATP.
    b. in an energetically unfavorable direction always coupled to another reaction or source
    of energy.
    c. in an energetically unfavorable direction driven only by the flow of another molecule
    across a membrane.
    d. in an energetically favorable direction coupled to the hydrolysis of ATP.
    e. of all molecules simultaneously, against their concentration gradients, across the
    membrane.

Answer 23

b. in an energetically unfavorable direction always coupled to another reaction or source
of energy.

Question 24

27. The Na+ and K+ ion gradients across the plasma membrane are produced primarily by
    the
    a. permeability of these ions across the lipid bilayer.
    b. ratio of these ions in the blood.
    c. action of the Na+
    -K+ pump.
    d. flow of these ions through voltage-gated channels.
    e. passive flow of these ions through channels.

Answer 24

c. action of the Na+

- K+ pump

Question 25

28. What percent of the ATP in a typical animal cell is consumed by the Na+ - K+ pump? a. 1% b. 10% c. 25% d. 50% e. 66%

Answer 25

c. 25%

Question 26

29. Calcium levels remain low in the cytosol a. only to ensure that calcium does not precipitate inside the cells. b. therefore, transient calcium increases can be used as intracellular signals. c. so that calcium does not accumulate in mitochondria. d. to allow extracellular calcium to drive import of other ions. e. All of the above

Answer 26

b. therefore, transient calcium increases can be used as intracellular signals.

Question 27

30. Bacteria, fungi, and plants cells use a gradient of _______ ions across their plasma membranes to drive transport of other molecules into the cells. a. Na+ b. K+ c. H+ d. Ca2+ e. OH–

Answer 27

c. H+

Question 28

``` 31. Cystic fibrosis is a genetic disease in which thick mucus accumulates over several epithelia and eventually blocks the pulmonary airways. The molecular basis of this disease is the production of a defective a. mucin. b. chloride channel. c. Na+ -K+ pump. d. Na+ -Ca2+ transporter. e. MDR transporter. ```

Answer 28

b. chloride channel.

Question 29

``` 32. Gene therapy for cystic fibrosis involves transfer into bronchial epithelia of the _______ gene. a. CFTR b. mucin c. Na+ -K+ pump d. Na+ -Ca2+ transporter e. MDR transporter ```

Answer 29

a. CFTR

Question 30

33. The MDR ABC transporter functions in a number of animal cells to transport a. glucose into cells. b. ions into cells. c. poisons and drugs out of cells. d. ATP out of cells. e. amino acids across epithelia

Answer 30

c. poisons and drugs out of cells.

Question 31

34. What is the role of tight junctions in the transport of glucose across the intestinal epithelium? a. They open and allow glucose to pass between the epithelial cells. b. They keep the Na+-K+ pumps in the apical membrane only. c. They keep the Na+-glucose cotransporter in the apical membrane and the glucosefacilitated transporter in the basolateral membrane. d. They keep the glucose-facilitated transporter in the apical membrane and the Na+-glucose cotransporter in the basolateral membrane. e. They keep glucose from passing into the epithelial cells

Answer 31

c. They keep the Na+-glucose cotransporter in the apical membrane and the glucosefacilitated transporter in the basolateral membrane.

Question 32

``` 35. Coupled transport of glucose and Na+ into the intestinal epithelial cell is an example of a. facilitated diffusion. b. symport. c. antiport. d. transcytosis. e. endocytosis ```

Answer 32

b. symport.

Question 33

36. The functioning of the Na+ - Ca2+ transporter in the plasma membrane is an example of a. facilitated diffusion. b. symport. c. antiport. d. transcytosis. e. endocytosis

Answer 33

c. antiport.

Question 34

37. Phagocytosis involves movement of the cell surface by a. actin-based motility. b. microtubule-based motility. c. clathrin-based vesicle formation. d. dynamin-based vesicle formation. e. claudin-based vesicle formation.

Answer 34

c. clathrin-based vesicle formation.

Question 35

39. Phagocytosis is the main function of what two types of human white blood cells? a. Macrophages and T lymphocytes b. Platelets and neutrophils c. Macrophages and neutrophils d. Eosinophils and macrophages e. Eosinophils and T lymphocytes

Answer 35

c. Macrophages and neutrophils

Question 36

40. Cholesterol is taken up into most cells of the body by a. phagocytosis. b. receptor-mediated endocytosis. c. simple diffusion. d. active transport. e. caveolae formation

Answer 36

b. receptor-mediated endocytosis.

Question 37

41. Brown and Goldstein discovered the mechanism of cholesterol uptake by studying fibroblasts from children with which disease? a. Chronic fatigue syndrome b. Familial hypercholesterolemia c. Lupus erythematosis d. Cystic fibrosis e. Essential hypertension

Answer 37

b. Familial hypercholesterolemia

Question 38

42. Coated pits are converted to coated vesicles by formation of rings of the protein a. caveolin. c c. COPI. d. dynamin. e. COPII.

Answer 38

42. Coated pits are converted to coated vesicles by formation of rings of the protein a. caveolin. b. clathrin. c. COPI. d. dynamin. e. COPII.

Question 39

1. What is the primary reason that mammalian red blood cells are used in the study of the plasma membrane? a. There are a lot of them and they are easily obtained. b. They contain more plasma membrane than any other cell type. c. They are of particular interest because they are made up of a lipid monolayer. d. They lack nuclei and membrane-bounded organelles.

Answer 39

d. They lack nuclei and membrane-bounded organelles.

Question 40

2. Two examples of membrane lipids present in small amounts are a. cholesterol and phosphatidylcholine. b. glycolipids and phosphatidylinositol. c. phosphatidylcholine and sphingomyelin. d. phosphatidylethanolamine and phosphatidylserine.

Answer 40

b. glycolipids and phosphatidylinositol.

Question 41

3. Which of the following lipids are distinctly enriched in lipid rafts? a. Cholesterol and sphingolipids b. Glycolipids and phosphatidylinositol c. Phosphatidylcholine and sphingomyelin d. Phosphatidylethanolamine and phosphatidylserine

Answer 41

a. Cholesterol and sphingolipids

Question 42

4. Which of the following will not solubilize a typical peripheral membrane protein? a. Detergent b. Extreme pH c. High salt d. Mildly hypertonic saline

Answer 42

d. Mildly hypertonic saline

Question 43

5. A feature common to most transmembrane proteins is a. a phosphorylated exterior domain. b. a structure consisting almost exclusively of β-sheets. c. an amino acid sequence rich in acidic residues. d. an α-helical region of about 20 to 25 hydrophobic amino acids.

Answer 43

d. an α-helical region of about 20 to 25 hydrophobic amino acids.

Question 44

6. An example of an integral membrane protein that does not contain a transmembrane α helix is a. band 3. b. glycophorin. c. glycosylphosphatidylinositol (GPI) anchors. d. spectrin

Answer 44

c. glycosylphosphatidylinositol (GPI) anchors.

Question 45

7. Membrane proteins are able to move a. from the inner to the outer surface of a membrane. b. laterally within the plane of a membrane. c. from apical to basal surfaces of intestinal epithelial cells. d. only if attached to microtubules or microfilaments.

Answer 45

b. laterally within the plane of a membrane.

Question 46

8. Specific recognition between cell types such as leukocytes and endothelial cells of blood vessels is mediated by cell-surface glycoproteins called a. selectins. b. fibronectins. c. spectrins. d. porins

Answer 46

a. selectins.

Question 47

9. Which of the following statements about the glucose transporter is false? a. It transports glucose across the plasma membrane via a mechanism called “facilitated diffusion. ” b. It has 12 α-helical transmembrane segments. c. A conformational change in the transporter is involved in the transport process. d. Flow through it is unidirectional.

Answer 47

d. Flow through it is unidirectional.

Question 48

10. Which of the following statements about ion channels is true? a. They are opened either by the binding of ligands or by changes in electric potential across the membrane. b. They require ATP. c. They are open most of the time. d. The rate of transport is slow compared to the rate of transport via carrier proteins.

Answer 48

a. They are opened either by the binding of ligands or by changes in electric potential across the membrane.

Question 49

11. Which of the following is true about the relative concentrations of Na+ and K+ inside and outside a typical mammalian cell? a. The concentration of Na+ and K+ outside the cell is about 30 times higher than inside the cell. b. The concentration of Na+ outside the cell is about 30 times higher than inside, and the concentration of K+ inside the cell is 10 to 30 times higher than outside. c. The concentration is the same for both ions, but there is a Cl– ion concentration gradient across the plasma membrane. d. The concentration of Na+ inside the cell is 30 times higher than outside, and the concentration of K+ outside the cell is 10 times higher than inside.

Answer 49

b. The concentration of Na+ outside the cell is about 30 times higher than inside, and the concentration of K+ inside the cell is 10 to 30 times higher than outside.

Question 50

12. The resting plasma membrane potential as described by the Nernst equation is the sum of the movement of many ions. However, in practice, the movement of _______, a single ion, is the major component determining membrane potential. a. Ca2+ b. Cl– c. K+ d. Na+

Answer 50

c. K+

Question 51

``` 13. Although Na+ is smaller than K+ , its passage through the K+ channel is blocked by the a. CO2 filter. b. negativity filter. c. positivity filter. d. selectivity filter. ```

Answer 51

d. selectivity filter.

Question 52

14. Active transport differs from facilitated diffusion in that a. ions are not transported via active transport. b. active transport requires a protein component, whereas facilitated diffusion occurs by simple diffusion through the plasma membrane. c. active transport involves the transport of molecules up their concentration gradient. d. active transport involves a conformational change in the transport molecule.

Answer 52

c. active transport involves the transport of molecules up their concentration gradient.

Question 53

``` 15. Transport of glucose into the intestinal epithelium is driven by ion gradients established by the a. ATP pump. b. H+ pump. c. K+ channel. d. Na+ -K+ pump. ```

Answer 53

d. Na+ | - K+ pump.

Question 54

16. Which of the following statements about ABC transporters is false? a. Each family member has an ATP-binding cassette. b. Each member of the family is a Cl– channel. c. This the largest family of membrane transporters in humans. d. Each member of the family has shared domain structure features.

Answer 54

b. Each member of the family is a Cl– channel.

Question 55

17. The ingestion of large particles by cells is a form of endocytosis known as a. fluid phase endocytosis. b. pinocytosis. c. phagocytosis. d. transcytosis

Answer 55

c. phagocytosis.

Question 56

18. Which of the following is not involved in receptor-mediated endocytosis? a. Clathrin b. Adaptor proteins c. Internalization signals d. Pseudopodia

Answer 56

b. Adaptor proteins

Question 57

19. LDL uptake by cells is one of the functions of a. receptor-mediated endocytosis. b. phagocytosis. c. caveolae. d. ABC transporters

Answer 57

a. receptor-mediated endocytosis.

Question 58

with a. adaptor proteins. b. caveolin. c. clathrin. d. dynamin.

Answer 58

c. clathrin.

Question 59

21. The pH of endosomes and lysosomes is a. acidic. b. alkaline. c. neutral. d. unknown

Answer 59

a. acidic.