Test Bank Exam Flashcards
1
Q
Functions of the Plasma Membrane
A
selective barrier to the passage of molecules, sensor through which the cell receives signals from the environment, site for uptake of macromolecules into the cell, site for RNA synthesis.
2
Q
The plasma membrane barrier to passive diffusion is primarily a function of the membrane’s
A
Phospholipids
3
Q
Mammalian erythrocytes (red blood cells) are particularly useful for studies of the plasma membrane because
A
they have only one membrane, the plasma membrane
4
Q
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 twice
5
Q
How are plasma membrane phospholipids distributed?
A
Asymmetrically between the two membrane halves
6
Q
Cholesterol is present in the membranes of all
A
Animal Cells
7
Q
Plasma membrane glycolipids are found
A
exclusively in the outer leaflet
8
Q
Clusters of sphingolipids, cholesterol, and membrane proteins that move together laterally in the plane of the plasma membrane are called
A
Lipid rafts
9
Q
If a suspension of cells is frozen and fractured, the most likely path of the fracture plane will be
A
between the two leaflets of the cell membrane
10
Q
The two erythrocyte proteins, glycophorin and band 3, are examples of
A
transmembrane proteins
11
Q
Porins form membrane channels whose structure is formed by a
A
barrel of β sheets.
12
Q
Above the temperature at which lipids are fluid, membrane proteins are able to move
A
laterally in the plane of a membrane
13
Q
Specific recognition between cell types such as leukocytes and endothelial cells of blood vessels is mediated by cell-surface glycoproteins called
A
selectins
14
Q
Molecules that diffuse passively across the plasma membrane most rapidly are
A
small and hydrophobic
15
Q
Facilitated diffusion differs from passive diffusion in that facilitated diffusion is
A
mediated by a protein carrier or channel
16
Q
The glucose-facilitated diffusion transporter can transport glucose
A
into or out of the cell
17
Q
Channels that open in response to neurotransmitters or other signal molecules are called
A
ligand-gated channels
18
Q
What describes the relative concentrations of ions in a typical mammalian cell?
A
K+ higher inside, Na+ and Cl– higher outside
19
Q
The resting potential of a typical eukaryotic cell is _______ mV
A
-60
20
Q
The Nernst equation allows you to calculate the
A
equilibrium potential due to one ion
21
Q
The flow of which ion makes the largest contribution to the resting potential?
A
K+
22
Q
What would be the resting potential across an artificial membrane if all charged molecules on both sides were equally permeable?
A
0 mV
23
Q
Voltage-sensitive K+ channels are one-thousand times more permeable to K+ than to Na+ because
A
a selectivity filter removes the water molecules from K+ ions but not from Na+ ions
24
Q
Active transport is transport
in
A
an energetically unfavorable direction always driven by hydrolysis of ATP
25
The Na+ and K+ ion gradients across the plasma membrane are produced primarily by the
action of the Na+-K+ pump.
26
What percent of the ATP in a typical animal cell is consumed by the Na+-K+ pump?
25%
27
Calcium levels remain low in the cytosol, therefore
transient calcium increases can be used as intracellular signals
28
Bacteria, fungi, and plants cells use a gradient of _______ ions across their plasma membranes to drive transport of other molecules into the cells.
Ca2+
29
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
chloride channel
30
Gene therapy for cystic fibrosis involves transfer into bronchial epithelia of the _______ gene.
CFTR
31
The MDR ABC transporter functions in a number of animal cells to transport
poisons and drugs out of cells
32
What is the role of tight junctions in the transport of glucose across the intestinal epithelium?
They keep the Na+-glucose cotransporter in the apical membrane and the glucose- facilitated transporter in the basolateral membrane.
33
Coupled transport of glucose and Na+ into the intestinal epithelial cell is an example of
symport
34
The functioning of the Na+-Ca2+ transporter in the plasma membrane is an example of
antiport
35
Phagocytosis involves movement of the cell surface by
actin-based motility
36
Aged red blood cells are removed from circulation by macrophages in the
spleen
37
Phagocytosis is the main function of what two types of human white blood cells?
Macrophages and neutrophils
38
Cholesterol is taken up into most cells of the body by
receptor-mediated endocytosis
39
Brown and Goldstein discovered the mechanism of cholesterol uptake by studying fibroblasts from children with which disease?
Familial hypercholesterolemia
40
Coated pits are converted to coated vesicles by formation of rings of the protein
Clathrin
41
Signaling by the steroid hormone estrogen is an example of _______ signaling.
endocrine
42
Signaling by neurotransmitters is an example of _______ signaling.
paracrine
43
Stimulation of T lymphocytes, leading to their synthesis of a growth factor resulting in T lymphocyte proliferation, is an example of _______ signaling.
autocrine
44
Signaling by cadherins is an example of _______ signaling
direct cell-to-cell
45
The hormone that triggers insect metamorphosis from larva to adult is
ecdysone
46
Steroid hormones usually act via receptors that
bind to DNA
47
Which of the following signal molecules binds to nuclear receptors?
Retinoic acid
48
A glucocorticoid binding to its receptor stimulates
formation of a receptor dimer that binds to and activates a gene
49
Nitric oxide is a signal molecule that can
diffuse across cell membranes and directly alter the activity of intracellular enzymes
50
Nitric oxide (NO) is considered a paracrine signal molecule because it
is unstable, with a short half-life
51
NO-synthase produces NO from the amino acid
arginine
52
Carbon monoxide can be released by brain cells and stimulates
guanylate cyclase and blood vessel dilation
53
Neurotransmitters act by binding to receptors that are
ligand-gated ion channels
54
Which of the following stimulates fibroblasts to proliferate and thus heal a wound?
PDGF
55
Peptide hormones and growth factors act on target cells by binding to cell surface and _______ receptors.
soluble extracellular
56
Aspirin inhibits _______ synthesis.
prostaglandin
57
All eicosanoids are synthesized from
arachidonic acid
58
In plants, cytokinins stimulate
cell division
59
In plant cells, auxin binds to a
receptor ubiquitin ligase that stimulates the degradation of transcriptional repressors, resulting in activation of genes
60
The G protein that activates adenylyl cyclase is a
heterotrimeric G protein that separates into alpha and beta gamma subunits
61
The GTP on the G protein that is linked to adenylyl cyclase is split to GDP and Pi
in the inactive state
62
In an active state of a G protein,
the alpha and beta gamma subunits both can bind to target proteins
63
Cholera toxin inhibits the ability of the alpha subunit of Gs to split GTP. If you treated cells with cholera toxin, the resulting effect would be _______ of adenylyl cyclase.
stimulation
64
The effect of acetylcholine on heart muscle cells is to
decrease the rate of beating
65
Acetylcholine’s effect on heart muscle cells results from the activation of receptors that _______ channels.
open K+
66
The major function of cAMP in animal cells is to activate
protein kinase A
67
Protein kinase A is activated by
binding of cAMP to its catalytic subunits
68
Which of the following is not considered a second messenger?
Ecdysone
69
Protein kinase A regulates glycogen metabolism by phosphorylating glycogen synthase and
phosphorylase kinase
70
Protein kinase A regulates glycogen metabolism by _______ glycogen synthase and _______ glycogen phosphorylase.
inactivating; activating
71
CREB is activated by
phosphorylation by protein kinase A in the nucleus
72
Which of the following correctly describes how protein kinase A can activate genes?
Cytosolic protein kinase A is activated by cAMP to release the catalytic subunits, which move into the nucleus and phosphorylate CREB
73
The response initiated by protein kinase A is terminated by
dephosphorylation of phosphoproteins by protein phosphatase 1
74
Rhodopsin in the vertebrate retinal photoreceptor cells results in a change in the second messenger _______, leading to the opening of ion channels in the plasma membrane and the production of a nerve impulse.
cGMP
75
The cell walls of bacteria are a copolymer of _______ and _______.
polysaccharides; peptides
76
Gram-positive bacteria have a
thick peptidoglycan wall outside the plasma membrane
77
Which of the following antibiotics inhibits the synthesis of bacterial cell walls?
Penicillin
78
Fungal cell walls are built primarily of
chitin
79
The polysaccharide chains of the bacterial cell walls are made of alternating N- _______ and N-_______ acid.
acetylglucosamine; acetylmuramic
80
Plant cell walls are cellulose fibrils in a matrix of
pectin and hemicellulose
81
The structural polysaccharide of fungal cell walls is the same polysaccharide found in insect
exoskeletons
82
Pectins form a _______ network in plant cell walls
gel-like
83
Secondary cell walls are stronger than primary cell walls because secondary cell walls contain
layers of cellulose fibrils at various orientations to one another
84
Cellulose synthase in plants is located
in the plasma membrane
85
The direction of cellulose microfibril synthesis in elongating plant cells is
perpendicular to the direction of microtubules under the plasma membrane
86
Which of the following statements about Gram-negative bacteria and Gram-positive bacteria is true?
a. Only Gram-positive bacteria have a double layer of plasma membrane.
b. Gram negative bacteria have much thicker cell walls than Gram-positive bacteria.
c. Gram-positive bacteria have no plasma membrane, only a cell wall.
d. Gram-negative bacteria are surrounded by a thin cell wall beneath an outer membrane.
d. Gram-negative bacteria are surrounded by a thin cell wall beneath an outer membrane.
87
Gram-negative bacteria contain _______ which, when released into the bloodstream, cause fever, low blood pressure, and inflammation.
lipopolysaccaride
88
The principal component of the cell walls of both Gram-positive bacteria and Gram- negative bacteria is
peptidoglycan
89
In plants, primary and secondary cell walls, though distinctly different, share all of the following molecules except
a. cellulose
b. hemicelluloses
c. pectin
d. peptidoglycans
d. peptidoglycans
90
The thin, sheetlike basal laminae are found
under epithelia
91
The major protein of the extracellular matrix of animal cells is
collagen
92
Collagens commonly contain the three repeating amino acids: _______, proline, and _______.
glycine; hydroxyproline
93
Basal laminae are a meshwork of fibrils composed primarily of type _______ collagen.
IV
94
Tissue cells are connected to the extracellular matrix by receptors that bind to an adhesive protein called
integrin
95
Integrins are
transmembrane proteins
96
Integrins bind to
collagen, fibronectin, laminin
97
The smallest amino acid is
glycine
98
Vitamin C deficiency may lead to scurvy, a disease characterized by skin lesions and blood vessel hemorrhages due to weakened connective tissue. Vitamin C deficiency has this effect because the vitamin is
a critical structural component of collagen
99
The major cell surface receptor(s) responsible for the attachment of cells to the extracellular matrix is (are)
integrins
100
Which of the following is the major family of calcium-mediated cell-surface adhesion molecules?
Cadherins
101
If developing pre-nerve cells expressing only N-cadherin on their surfaces were mixed with epithelial cells expressing only E-cadherin, which of the following would be the likely result?
Nerve cells would adhere to one another and epithelial cells would adhere to one another
102
Adherens junctions are linked to cytoplasmic
actin filaments
103
Desmosomes are linked to cytoplasmic
intermediate filaments
104
Which of the following molecules mediate the association of actin filaments with the cadherins in an adherens junction?
α- and β-catenin
105
Cell adhesion molecules can be divided into four major groups. What are they?
Selecting, integrins, Ig superfamily, cadherins
106
The molecules that recruit cadherins to the sites of junction formation are called
nectins
107
Desmosomes are held together by the adhesion of the two desmosomal cadherins: _______ and _______.
desmoglein; desmocollin
108
A junctional complex consists of a tight junction associated with both adherens junctions and
desmosomes
109
The function of gap junctions is to
provide direct communication between cells
110
Which of the following can pass through gap junctions?
cAMP and calcium ions
111
Adhesion of plant cells is mediated by a pectin-rich region of the cell wall called the
middle lamella
112
The communicating junctions between plant cells are called
plasmodesmata
113
What is the difference between Gram-positive and Gram-negative bacteria?
Gram-positive bacteria are surrounded by a single membrane, whereas Gram-negative bacteria are surrounded by a double membrane, with an outer membrane that is porous to ions and small molecules.
114
A mutation in the bacterial gene encoding crescentin would likely have an effect on which type of bacteria?
Curved or spiral-shaped
115
The basic structural polysaccharide of fungal cell walls, crab shells, and insect exoskeletons is
chitin
116
Primary plant cell walls are cross-linked by
hemicellulose
117
Cellulose, chitin, and hyaluronan are all deposited extracellularly by
plasma membrane enzyme complexes
118
Animal cells are embedded in a(n)
extracellular matrix
119
Fibrous structural proteins of the extracellular matrix are embedded in gels formed from polysaccharides called
glycosaminoglycans (GAGs)
120
The major function of adhesion proteins such as fibronectin is to
link collagen, proteoglycans, and cells containing integrins
121
The cell–cell interactions mediated by the selectins, integrins, and most members of the Ig superfamily are _______ interactions in which the cytoskeletons of adjacent cells are not linked to one another.
transient
122
Homophilic interactions between cells involve interactions
among adhesion molecules of the same molecular class
123
Adherens junctions and desmosomes may be distinguished from each other on the basis of
the linkage of cadherins either to actin filaments or to intermediate filaments, respectively
124
A major function of tight junctions is to
seal the space between adjacent cells to provide, for example, a barrier to sugar diffusion across an epithelial cell layer
125
The junctions between animal cells that allow the free passage of molecules smaller than approximately 1,000 daltons are called
gap junctions
126
_______, although structurally different from gap junctions in animal cell tissues, may be thought of as the functional equivalent of gap junctions in plants.
Plasmodesmata
127
Specific recognition between cell types such as leukocytes and endothelial cells of blood vessels is mediated by cell-surface glycoproteins called
selectins
