Deck 15: The Plasma Membrane

Question 1

The plasma membrane functions as a

A) selective barrier to the passage of molecules.
B) site for the uptake of macromolecules into the cell.
C) site for cell-cell interactions.
D) All of the above

Answer 1

D

Question 2

The plasma membrane's barrier to passive diffusion is primarily a function of the membrane's

A) phospholipids.
B) cholesterol.
C) proteins.
D) glycoproteins.

Answer 2

A

Question 3

Gorter and Grendel's classic experiment allowed them to observe that the erythrocyte plasma membrane contains _______ the surface area of the erythrocytes.

A) enough lipid to occupy a monolayer equal to
B) enough lipid to occupy a monolayer equal to twice
C) less lipid than would occupy a monolayer equal to
D) enough lipid to occupy a monolayer equal to one-half

Answer 3

B

Question 4

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.

Question 5

Cholesterol is present in the membranes of all

A) cells.
B) eukaryotic cells.
C) animal cells.
D) plant cells.

Question 6

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.

Question 7

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.

Question 8

The two erythrocyte proteins glycophorin and band 3 are examples of

A) peripheral proteins.
B) transmembrane proteins.
C) cytoskeletal proteins.
D) $\beta$ -barrel proteins.

Question 9

Clusters of _______ in membrane proteins such as band 3 of the erythrocyte can define hydrophilic segments through which ions (for example, bicarbonate and chloride) can be transported.

A) oligosaccharide side chains
B) lipid modifications
C) transmembrane α helices
D) phosphorylation motifs

Question 10

Which of the following features of a membrane protein is never used as a membrane anchor?

A) C-terminal glycosylphosphatidyl inositol (GPI)
B) An N-terminal myristoyl group
C) Prenyl and palmitoyl group additions
D) Oligosaccharide side chains

Question 11

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.

Question 12

A major feature included in the updated fluid mosaic model is the

A) interaction of transmembrane proteins with the cytoskeleton.
B) restriction of glycolipids to the extracellular face of the plasma membrane.
C) presence of multiple pass transmembrane proteins.
D) presence of N-linked oligosaccharide side chains on glycoproteins at the cell surface.

Question 13

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.

Question 14

If a suspension of cells is frozen and fractured, the most likely path of the fracture plane will be

A) between the cell surface and the outside solution.
B) between the membrane and the cytoplasm of the cells.
C) through the middle of the cytoplasm.
D) between the two leaflets of the cell membranes.

Question 15

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 glucose-facilitated 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.

Question 16

Molecules that diffuse passively across the plasma membrane most rapidly are

A) small.
B) hydrophobic.
C) small and hydrophobic.
D) small and hydrophilic.

Question 17

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) mediated by a protein carrier or channel.
D) against the concentration gradient.

Question 18

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.

Question 19

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) amino acids across epithelia.

Question 20

Which of the following has the fastest rate of transport?

A) Channel-mediated diffusion
B) Facilitated diffusion
C) Active transport
D) All of the above are equally fast.

Question 21

In a typical mammalian cell, the concentration of _______ is higher on the inside, and the concentration of _______ is higher on the outside.

A) Na⁺ and Cl^-; K⁺
B) Na⁺; K⁺ and Cl^-
C) K⁺; Na⁺ and Cl^-
D) K⁺ and Cl^-; Na⁺

Question 22

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

Question 23

The resting potential of a typical eukaryotic cell is _______ mV.

A) 0
B) -60
C) +60
D) -100

Question 24

The Nernst equation allows one to calculate the

A) resting membrane potential.
B) equilibrium potential for each ion.
C) membrane potential when all channels are closed.
D) membrane potential when all channels are open.

Question 25

What would be the resting potential across an artificial membrane if all charged molecules on both sides were equally permeable?

A) -60 mV
B) +60 mV
C) 0 mV
D) -1 mV

Question 26

The flow of which ion makes the largest contribution to the resting potential?

A) K⁺
B) Na⁺
C) H⁺
D) Ca²⁺

Question 27

Voltage-sensitive K⁺ channels are 1,000 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 are more concentrated inside the cell than outside the cell.

Question 28

Cystic fibrosis is a genetic disease in which thick mucus accumulates over several types of epithelial cells, eventually blocking 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.

Question 29

Gene therapy for cystic fibrosis involves transfer of the _______ gene into bronchial epithelia.

A) CFTR
B) mucin
C) Na⁺-K⁺ pump
D) MDR transporter

Question 30

Active transport is transport in an energetically

A) unfavorable direction, always driven by hydrolysis of ATP.
B) unfavorable direction, always coupled to another reaction or source of energy.
C) unfavorable direction, driven only by the flow of another molecule across a membrane.
D) favorable direction, coupled to the hydrolysis of ATP.

Question 31

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.

Question 32

What percent of the ATP in a typical animal cell is consumed by the Na⁺-K⁺ pump?

A) 1%
B) 10%
C) 25%
D) 66%

Question 33

Calcium levels remain low in the cytosol

A) only to ensure that calcium does not precipitate inside the cells.
B) thus 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.

Question 34

Bacteria, fungi, and plants 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⁺

Question 35

Coupled transport of glucose and Na⁺ into the intestinal epithelial cell is an example of

A) facilitated diffusion.
B) symport.
C) antiport.
D) endocytosis.

Question 36

The functioning of the Na⁺-Ca²⁺ transporter in the plasma membrane is an example of

A) facilitated diffusion.
B) symport.
C) antiport.
D) endocytosis.

Question 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.

Question 38

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 T lymphocytes

Question 39

Cholesterol is taken up into most cells of the body by

A) phagocytosis.
B) receptor-mediated endocytosis.
C) simple diffusion.
D) caveolae formation.

Question 40

Brown and Goldstein discovered the mechanism of cholesterol uptake by studying fibroblasts from patients with which disease?

A) Chronic fatigue syndrome
B) Familial hypercholesterolemia
C) Lupus erythematosus
D) Cystic fibrosis

Question 41

Coated pits are converted to coated vesicles by formation of rings of the protein

A) caveolin.
B) clathrin.
C) COPI.
D) dynamin.

Question 42

The currently accepted model of membrane structure, proposed by Singer and Nicolson, is called the _______ model.

Question 43

The membrane-spanning portion of a single-pass transmembrane protein is usually a secondary structure called a(n) _______.

Question 44

The membrane-spanning portion of the protein porin (and proteins with similar structures in the outer membranes of mitochondria and chloroplasts) has a membrane-spanning secondary structure called a(n) _______.

Question 45

The potentially oncogenic signal-transmitting proteins Src and Ras are attached to the inner surface of the plasma membrane by covalent links to _______.

Question 46

Some plasma membrane proteins are immobilized by association with _______ proteins, other plasma membrane proteins, and the _______ matrix.

Question 47

The restriction of membrane protein movement between surfaces of intestinal epithelia is primarily due to the presence of _______ junctions between the epithelial cells.

Question 48

The plasma membrane of intestinal epithelial cells is divided into two domains: the _______ domain and the _______ domain.

Question 49

During facilitated diffusion of glucose, the glucose transporter changes its _______.

Question 50

The Na⁺ and K⁺ channels involved in the propagation of an action potential are _______-gated.

Question 51

The released neurotransmitters at a synapse are sensed by _______-gated channels.

Question 52

The selectivity filter in a K⁺ channel is able to _______ K⁺ but not Na⁺, which is smaller.

Question 53

Active transport can be driven by _______ hydrolysis or by _______ gradients.

Question 54

The cytoplasmic domain of ligand-bound LDL receptor binds to _______ proteins, which in turn associate with the _______ coat.

Question 55

The endocytic trafficking pathway of ligands and receptors in eukaryotic cells is often controlled by sequential differences in _______ between early endosomes, late endosomes, and lysosomes.

Question 56

Some endocytic receptors are _______ from endosomes, while others are _______ in lysosomes.

Question 57

Glycolipids are the major lipids in the plasma membrane.

Question 58

Phosphatidylcholine is the only major phospholipid in the plasma membrane.

Question 59

The outer membrane of mitochondria is the major site where porins are found in animal cells.

Question 60

The apical surface of intestinal epithelial cells is covered by a carbohydrate coat known as the glycocalyx.

Question 61

Estrogen is an example of a hormone to which the plasma membrane is impermeable.

Question 62

Facilitated diffusion is a lipid-mediated process.

Question 63

The major ATPase maintaining the plasma membrane potential is the Na⁺-K⁺ pump.

Question 64

The K⁺-glucose transporter is an example of a symport that actively transports glucose into cells.

Question 65

Phagocytosis is an example of macropinocytosis.

Question 66

Defects in the human LDL receptor can cause the disease hypercholesterolemia.

Question 67

Caveolae are rich in cholesterol and other constituents of lipid rafts.

Question 68

What are integral membrane proteins?

Question 69

What are peripheral membrane proteins?

Question 70

Frye and Edidin demonstrated the mobility of membrane proteins with the use of fused human and mouse cells. Briefly describe the results of their experiment.

Question 71

What is one function of cell-surface carbohydrates?

Question 72

How does the structure of a transport protein such as a glucose transporter create an aqueous environment in which glucose may be transported across the plasma membrane?

Question 73

How is rapid transport of water across the plasma membrane achieved?

Question 74

Explain how phagocytosis differs mechanistically from other types of endocytosis.

Question 75

Define endocytosis and explain the process by which it operates.

Question 76

What is the mechanism by which cells take up specific macromolecules?

Question 77

Where is clathrin located in cells?

Question 78

Describe a role or function for coated pits in the process of receptor-mediated endocytosis.

Question 79

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 larger plasma membranes 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.

Question 80

Two examples of membrane lipids that are present in small amounts are

A) cholesterol and phosphatidylcholine.
B) glycolipids and phosphatidylinositol.
C) phosphatidylcholine and sphingomyelin.
D) phosphatidylethanolamine and phosphatidylserine.