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Test Bank Exam Flashcards

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Biology 101 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.

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2
Q

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

A

Phospholipids

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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

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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

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5
Q

How are plasma membrane phospholipids distributed?

A

Asymmetrically between the two membrane halves

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6
Q

Cholesterol is present in the membranes of all

A

Animal Cells

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7
Q

Plasma membrane glycolipids are found

A

exclusively in the outer leaflet

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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

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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

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10
Q

The two erythrocyte proteins, glycophorin and band 3, are examples of

A

transmembrane proteins

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11
Q

Porins form membrane channels whose structure is formed by a

A

barrel of β sheets.

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12
Q

Above the temperature at which lipids are fluid, membrane proteins are able to move

A

laterally in the plane of a membrane

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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

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14
Q

Molecules that diffuse passively across the plasma membrane most rapidly are

A

small and hydrophobic

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15
Q

Facilitated diffusion differs from passive diffusion in that facilitated diffusion is

A

mediated by a protein carrier or channel

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16
Q

The glucose-facilitated diffusion transporter can transport glucose

A

into or out of the cell

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17
Q

Channels that open in response to neurotransmitters or other signal molecules are called

A

ligand-gated channels

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18
Q

What describes the relative concentrations of ions in a typical mammalian cell?

A

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

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19
Q

The resting potential of a typical eukaryotic cell is _______ mV

A

-60

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20
Q

The Nernst equation allows you to calculate the

A

equilibrium potential due to one ion

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21
Q

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

A

K+

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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

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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

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24
Q

Active transport is transport

in

A

an energetically unfavorable direction always driven by hydrolysis of ATP

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25
Q

The Na+ and K+ ion gradients across the plasma membrane are produced primarily by the

A

action of the Na+-K+ pump.

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26
Q

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

A

25%

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27
Q

Calcium levels remain low in the cytosol, therefore

A

transient calcium increases can be used as intracellular signals

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28
Q

Bacteria, fungi, and plants cells use a gradient of _______ ions across their plasma membranes to drive transport of other molecules into the cells.

A

Ca2+

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29
Q

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

chloride channel

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30
Q

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

A

CFTR

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31
Q

The MDR ABC transporter functions in a number of animal cells to transport

A

poisons and drugs out of cells

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32
Q

What is the role of tight junctions in the transport of glucose across the intestinal epithelium?

A

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

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33
Q

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

A

symport

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34
Q

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

A

antiport

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35
Q

Phagocytosis involves movement of the cell surface by

A

actin-based motility

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36
Q

Aged red blood cells are removed from circulation by macrophages in the

A

spleen

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37
Q

Phagocytosis is the main function of what two types of human white blood cells?

A

Macrophages and neutrophils

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38
Q

Cholesterol is taken up into most cells of the body by

A

receptor-mediated endocytosis

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39
Q

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

A

Familial hypercholesterolemia

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40
Q

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

A

Clathrin

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41
Q

Signaling by the steroid hormone estrogen is an example of _______ signaling.

A

endocrine

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42
Q

Signaling by neurotransmitters is an example of _______ signaling.

A

paracrine

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43
Q

Stimulation of T lymphocytes, leading to their synthesis of a growth factor resulting in T lymphocyte proliferation, is an example of _______ signaling.

A

autocrine

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44
Q

Signaling by cadherins is an example of _______ signaling

A

direct cell-to-cell

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45
Q

The hormone that triggers insect metamorphosis from larva to adult is

A

ecdysone

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46
Q

Steroid hormones usually act via receptors that

A

bind to DNA

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47
Q

Which of the following signal molecules binds to nuclear receptors?

A

Retinoic acid

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48
Q

A glucocorticoid binding to its receptor stimulates

A

formation of a receptor dimer that binds to and activates a gene

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49
Q

Nitric oxide is a signal molecule that can

A

diffuse across cell membranes and directly alter the activity of intracellular enzymes

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50
Q

Nitric oxide (NO) is considered a paracrine signal molecule because it

A

is unstable, with a short half-life

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51
Q

NO-synthase produces NO from the amino acid

A

arginine

52
Q

Carbon monoxide can be released by brain cells and stimulates

A

guanylate cyclase and blood vessel dilation

53
Q

Neurotransmitters act by binding to receptors that are

A

ligand-gated ion channels

54
Q

Which of the following stimulates fibroblasts to proliferate and thus heal a wound?

A

PDGF

55
Q

Peptide hormones and growth factors act on target cells by binding to cell surface and _______ receptors.

A

soluble extracellular

56
Q

Aspirin inhibits _______ synthesis.

A

prostaglandin

57
Q

All eicosanoids are synthesized from

A

arachidonic acid

58
Q

In plants, cytokinins stimulate

A

cell division

59
Q

In plant cells, auxin binds to a

A

receptor ubiquitin ligase that stimulates the degradation of transcriptional repressors, resulting in activation of genes

60
Q

The G protein that activates adenylyl cyclase is a

A

heterotrimeric G protein that separates into alpha and beta gamma subunits

61
Q

The GTP on the G protein that is linked to adenylyl cyclase is split to GDP and Pi

A

in the inactive state

62
Q

In an active state of a G protein,

A

the alpha and beta gamma subunits both can bind to target proteins

63
Q

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.

A

stimulation

64
Q

The effect of acetylcholine on heart muscle cells is to

A

decrease the rate of beating

65
Q

Acetylcholine’s effect on heart muscle cells results from the activation of receptors that _______ channels.

A

open K+

66
Q

The major function of cAMP in animal cells is to activate

A

protein kinase A

67
Q

Protein kinase A is activated by

A

binding of cAMP to its catalytic subunits

68
Q

Which of the following is not considered a second messenger?

A

Ecdysone

69
Q

Protein kinase A regulates glycogen metabolism by phosphorylating glycogen synthase and

A

phosphorylase kinase

70
Q

Protein kinase A regulates glycogen metabolism by _______ glycogen synthase and _______ glycogen phosphorylase.

A

inactivating; activating

71
Q

CREB is activated by

A

phosphorylation by protein kinase A in the nucleus

72
Q

Which of the following correctly describes how protein kinase A can activate genes?

A

Cytosolic protein kinase A is activated by cAMP to release the catalytic subunits, which move into the nucleus and phosphorylate CREB

73
Q

The response initiated by protein kinase A is terminated by

A

dephosphorylation of phosphoproteins by protein phosphatase 1

74
Q

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.

A

cGMP

75
Q

The cell walls of bacteria are a copolymer of _______ and _______.

A

polysaccharides; peptides

76
Q

Gram-positive bacteria have a

A

thick peptidoglycan wall outside the plasma membrane

77
Q

Which of the following antibiotics inhibits the synthesis of bacterial cell walls?

A

Penicillin

78
Q

Fungal cell walls are built primarily of

A

chitin

79
Q

The polysaccharide chains of the bacterial cell walls are made of alternating N- _______ and N-_______ acid.

A

acetylglucosamine; acetylmuramic

80
Q

Plant cell walls are cellulose fibrils in a matrix of

A

pectin and hemicellulose

81
Q

The structural polysaccharide of fungal cell walls is the same polysaccharide found in insect

A

exoskeletons

82
Q

Pectins form a _______ network in plant cell walls

A

gel-like

83
Q

Secondary cell walls are stronger than primary cell walls because secondary cell walls contain

A

layers of cellulose fibrils at various orientations to one another

84
Q

Cellulose synthase in plants is located

A

in the plasma membrane

85
Q

The direction of cellulose microfibril synthesis in elongating plant cells is

A

perpendicular to the direction of microtubules under the plasma membrane

86
Q

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.

A

d. Gram-negative bacteria are surrounded by a thin cell wall beneath an outer membrane.

87
Q

Gram-negative bacteria contain _______ which, when released into the bloodstream, cause fever, low blood pressure, and inflammation.

A

lipopolysaccaride

88
Q

The principal component of the cell walls of both Gram-positive bacteria and Gram- negative bacteria is

A

peptidoglycan

89
Q

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

A

d. peptidoglycans

90
Q

The thin, sheetlike basal laminae are found

A

under epithelia

91
Q

The major protein of the extracellular matrix of animal cells is

A

collagen

92
Q

Collagens commonly contain the three repeating amino acids: _______, proline, and _______.

A

glycine; hydroxyproline

93
Q

Basal laminae are a meshwork of fibrils composed primarily of type _______ collagen.

A

IV

94
Q

Tissue cells are connected to the extracellular matrix by receptors that bind to an adhesive protein called

A

integrin

95
Q

Integrins are

A

transmembrane proteins

96
Q

Integrins bind to

A

collagen, fibronectin, laminin

97
Q

The smallest amino acid is

A

glycine

98
Q

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

a critical structural component of collagen

99
Q

The major cell surface receptor(s) responsible for the attachment of cells to the extracellular matrix is (are)

A

integrins

100
Q

Which of the following is the major family of calcium-mediated cell-surface adhesion molecules?

A

Cadherins

101
Q

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?

A

Nerve cells would adhere to one another and epithelial cells would adhere to one another

102
Q

Adherens junctions are linked to cytoplasmic

A

actin filaments

103
Q

Desmosomes are linked to cytoplasmic

A

intermediate filaments

104
Q

Which of the following molecules mediate the association of actin filaments with the cadherins in an adherens junction?

A

α- and β-catenin

105
Q

Cell adhesion molecules can be divided into four major groups. What are they?

A

Selecting, integrins, Ig superfamily, cadherins

106
Q

The molecules that recruit cadherins to the sites of junction formation are called

A

nectins

107
Q

Desmosomes are held together by the adhesion of the two desmosomal cadherins: _______ and _______.

A

desmoglein; desmocollin

108
Q

A junctional complex consists of a tight junction associated with both adherens junctions and

A

desmosomes

109
Q

The function of gap junctions is to

A

provide direct communication between cells

110
Q

Which of the following can pass through gap junctions?

A

cAMP and calcium ions

111
Q

Adhesion of plant cells is mediated by a pectin-rich region of the cell wall called the

A

middle lamella

112
Q

The communicating junctions between plant cells are called

A

plasmodesmata

113
Q

What is the difference between Gram-positive and Gram-negative bacteria?

A

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
Q

A mutation in the bacterial gene encoding crescentin would likely have an effect on which type of bacteria?

A

Curved or spiral-shaped

115
Q

The basic structural polysaccharide of fungal cell walls, crab shells, and insect exoskeletons is

A

chitin

116
Q

Primary plant cell walls are cross-linked by

A

hemicellulose

117
Q

Cellulose, chitin, and hyaluronan are all deposited extracellularly by

A

plasma membrane enzyme complexes

118
Q

Animal cells are embedded in a(n)

A

extracellular matrix

119
Q

Fibrous structural proteins of the extracellular matrix are embedded in gels formed from polysaccharides called

A

glycosaminoglycans (GAGs)

120
Q

The major function of adhesion proteins such as fibronectin is to

A

link collagen, proteoglycans, and cells containing integrins

121
Q

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.

A

transient

122
Q

Homophilic interactions between cells involve interactions

A

among adhesion molecules of the same molecular class

123
Q

Adherens junctions and desmosomes may be distinguished from each other on the basis of

A

the linkage of cadherins either to actin filaments or to intermediate filaments, respectively

124
Q

A major function of tight junctions is to

A

seal the space between adjacent cells to provide, for example, a barrier to sugar diffusion across an epithelial cell layer

125
Q

The junctions between animal cells that allow the free passage of molecules smaller than approximately 1,000 daltons are called

A

gap junctions

126
Q

_______, although structurally different from gap junctions in animal cell tissues, may be thought of as the functional equivalent of gap junctions in plants.

A

Plasmodesmata

127
Q

Specific recognition between cell types such as leukocytes and endothelial cells of blood vessels is mediated by cell-surface glycoproteins called

A

selectins

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