18
APOPTOSIS
TERMS TO LEARN
anti-apoptotic Bcl2 protein
anti-IAP
Apaf1
apoptosis
apoptosome
Bak
Bax
Bcl2
Bcl-XL
BH123 protein
BH3-only protein
caspase
cytochrome c
death-inducing signaling complex (DISC)
death receptor
executioner procaspase
extrinsic pathway
Fas
Fas ligand
IAP (inhibitor of apoptosis)
initiator procaspase
intrinsic pathway
procaspase
programmed cell death
survival factor
DEFINITIONS
Match the definition below with its term from the list above.
18–1 Protease that has a cysteine at its active site and cleaves its target proteins at
specific aspartic acids. caspase
18–2 Wheel-like assembly composed of seven copies of the Apaf-1/cytochrome c
complex. apoptosome
18–3 Form of cell death that leads to fragmentation of the DNA, shrinkage of the
cytoplasm, membrane changes and cell death, without lysis or damage to
neighboring cells. apoptosis
18–4 An assembly of several proteins, including intiator procaspases, on the
cytosolic portion of the Fas death receptor. DISC
18–5 Apoptosis program that is triggered by the binding of an extracellular signal
protein. Extrinsic pathway
18–6 Extracelluar signal molecule that inhibits apoptosis. Survival factor
18–7 Apoptosis program triggered by intracellular signals that cause release into
the cytosol of proteins from the mitochondrial intermembrane space. Intrinsic pathway
18–8 Intracellular ‘suicide’ program that allows cells to kill themselves in a controlled
way. Programmed cell death
18–9 Cell-surface molecule that triggers apoptosis when bound by an extracellular
signal protein. Death receptor
18–10 Inactive form of protease that operates in apoptosis at the start of the proteolytic
cascade. Initiator caspase
TRUE/FALSE
Decide whether each of these statements is true or false, and then explain why.
18–11 In normal adult tissues, cell death usually balances cell division. T
18–12 Mammalian cells that do not have cytochrome c should be resistant to apoptosis
induced by UV light. T
19
CADHERINS AND CELL–CELL ADHESION
TERMS TO LEARN
adherens junction
adhesion belt
anchoring junction
cadherin
cadherin superfamily
cell–cell adhesion
channel-forming junction
classical cadherin
connective tissue
desmosome junction
epithelia
epithelial tissue
homophilic
immunoglobulin (Ig) superfamily
integrin
nonclassical cadherin
occluding junction
PDZ domain
scaffold protein
selectin
signal-relaying junction
transmembrane adhesion protein
DEFINITIONS
Match each definition below with its term from the list above.
19–1 Member of a family of cell-surface carbohydrate-binding proteins that
mediate transient, Ca2+-dependent cell–cell adhesion in the bloodstream,
for example, between white blood cells and the endothelium of the blood
vessel wall.
19–2 Like-to-like protein interactions in which a molecule on one cell binds to an
identical, or closely related, molecule on an adjacent cell.
19–3 Type of anchoring junction, usually formed between two epithelial cells,
characterized by dense plaques of protein into which intermediate filaments
in the two adjoining cell insert.
19–4 Member of a large family of transmembrane proteins involved in the adhesion
of cells to the extracellular matrix and to each other.
19–5 Anchoring junction that connects actin filaments in one cell to those in the
next cell.
19–6 A member of a family of proteins that mediate Ca2+-dependent cell–cell
adhesion in animal tissues.
19–7 Beltlike anchoring junction that encircles the apical end of an epithelial cell
and attaches it to the adjoining cell.
TRUE/FALSE
Decide whether each of these statements is true or false, and then explain why.
19–8 Given the numerous processes inside cells that are regulated by changes in
Ca2+ concentration, it seems likely that Ca2+-dependent cell–cell adhesions
are also regulated by changes in Ca2+ concentration. F
19–9 Cadherins promote cell–cell interactions by binding to cadherin molecules
of the same or closely related subtype on adjacent cells.
19–10 The selectins on one cell promote transient cell–cell interactions by binding
to carbohydrate moieties on the surface of another cell.
19–11 Although cadherins and Ig family members are frequently expressed on the
same cells, the adhesions mediated by Ig molecules are much stronger and,
thus, are largely responsible for holding cells together.
TIGHT JUNCTIONS AND THE ORGANIZATION
OF EPITHELIA
TIGHT JUNCTIONS AND THE ORGANIZATION OF EPITHELIA
TERMS TO LEARN
apical
atypical protein kinase C (aPKC)
basal
occluding junction
Par3
Par6
planar cell polarity
polarized
septate junction
tight junction
Match each definition below with its term from the list above.
19–22 Describes a structural property of epithelial sheets, and their individual
cells, which have one surface attached to the basal lamina below and the
opposite surface exposed to the medium above.
19–23 Main type of occluding junction in invertebrates; it seals adjacent epithelial
cells together, preventing the passage of most dissolved molecules from one
side of the epithelial sheet to the other.
19–24 Main type of occluding junction in vertebrates; it seals adjacent epithelial
cells together, preventing the passage of most dissolved molecules from one
side of the epithelial sheet to the other.
19–25 Describes the tip of a cell. For an epithelial cell, it is the exposed free surface,
opposite to the surface attached to the basal lamina.
TRUE/FALSE
Decide whether each of these statements is true or false, and then explain why.
19–26 Virtually all epithelia are anchored to other tissues on their basal side and
free of such attachment on their apical side.
19–27 Tight junctions perform two distinct functions: they seal the space between
cells to restrict paracellular flow and they fence off membrane domains to
prevent the mixing of apical and basolateral proteins. T
19–28 Like the corresponding transport processes through the plasma membrane,
paracellular transport can be either active or passive.
19–29 Septate junctions are found only in insects.
PASSAGEWAYS FROM CELL TO CELL: GAP JUNCTIONS
AND PLASMODESMATA
TERMS TO LEARN
connexin
connexon
plasmodesmata
DEFINITIONS
Match each definition below with its term from the list above.
19–37 Communicating cell–cell junctions in plants in which a channel of cytoplasm
lined by plasma membrane connects two adjacent cells through a
small pore in their cell walls.
19–38 Water-filled pore in the plasma membrane formed by a ring of six protein
subunits, which link to an identical assembly in an adjoining cell to form a
continuous channel between the two cells.
TRUE/FALSE
Decide whether each of these statements is true or false, and then explain why.
19–39 Unlike conventional ion channels, individual gap-junction channels remain
open continuously once they are formed.
19–40 The cells in a plant can be viewed as forming a syncytium, in which many
cell nuclei share a common cytoplasm.
THE BASAL LAMINA
TERMS TO LEARN
basal lamina (basement membrane)
laminin-1
type IV collagen
DEFINITIONS
Match each definition below with its term from the list above.
19–46 Extracellular matrix protein found in basal laminae, where it forms a sheet-like
network.
19–47 Thin mat of extracellular matrix that separates epithelial sheets, and many
other types of cells such as muscle or fat cells, from connective tissue.
TRUE/FALSE
Decide whether each of these statements is true or false, and then explain why.
19–48 A sheet of basal lamina underlies all epithelia.
19–49 The basal lamina is constructed from components supplied by different cell
types, commonly by epithelial cells on one side and stromal cells on the other.
19–50 A proteoglycan in the basal lamina of the kidney glomerulus plays a critical
role in filtering the molecules that pass from the bloodsteam into the urine.
19–51 Most muscular dystrophy diseases (muscle-wasting diseases) arise from
defective components in the specialized basal lamina (sarcolemma) that
surrounds muscle fibers.
INTEGRINS AND CELL–MATRIX ADHESION
TERMS TO LEARN
anchorage dependence
focal adhesion kinase (FAK)
integrin
DEFINITIONS
Match each definition below with its term from the list above.
19–58 Cytoplasmic tyrosine kinase present at cell–matrix junctions in association
with the cytoplasmic tails of integrins.
19–59 Principal receptor on animal cells for binding most extracellular matrix proteins,
including collagens, fibronectin, and laminins.
19–60 Dependence of cell growth on attachment to a substratum.
TRUE/FALSE
Decide whether each of these statements is true or false, and then explain why.
19–61 Integrins can convert mechanical signals into molecular signals.
19–62 Various types of integrins connect extracellular binding sites to all the different
kinds of cytoskeletal elements, including actin, microtubules, and
intermediate filaments.
19–63 Integrins are thought to be rigid rods that span the membrane and link binding
sites outside the cell to those inside the cell.
THE EXTRACELLULAR MATRIX OF ANIMAL CONNECTIVE
TISSUES
TERMS TO LEARN
collagen glycosaminoglycan (GAG)
collagen fibril hyaluronan
elastin matrix metalloprotease
elastic fiber proteoglycan
fibril-associated collagen RGD sequence
fibrillar collagen serine protease
fibroblast type III fibronectin repeat
fibronectin
DEFINITIONS
Match each definition below with its term from the list above.
19–68 Fibrous protein rich in glycine and proline that, in its many forms, is a major
component of the extracellular matrix and connective tissues.
19–69 Complex network of polysaccharides (such as glycosaminoglycans or cellulose)
and proteins (such as collagens) secreted by cells that serves as a
structural element in tissues and also influences tissue development and
physiology.
19–70 General name for long, linear, highly charged polysaccharides composed of
a repeating pair of sugars, one of which is always an amino sugar, that is
found covalently linked to a protein core in the extracellular matrix.
19–71 Type of collagen molecule that assembles into ropelike structures and larger,
cablelike bundles.
19–72 Extracellular matrix protein that binds to cell-surface integrins to promote
adhesion of cells to the matrix and to provide guidance to migrating cells
during embryogenesis.
19–73 Hydrophobic protein that forms extracellular extensible fibers that give tissues
their stretchability and resilience.
19–74 Common cell type in connective tissue that secretes an extracellular matrix
rich in collagen and other extracellular matrix macromolecules.
TRUE/FALSE
Decide whether each of these statements is true or false, and then explain why.
19–75 The extracellular matrix is a relatively inert scaffolding that stabilizes the
structure of tissues.
19–76 One of the main chemical differences between proteoglycans and other glycoproteins
lies in the structure of their carbohydrate side chains: proteoglycans
mostly contain long, unbranched polysaccharide side chains, whereas
other glycoproteins contain much shorter, highly branched oligosaccharides.
19–77 Breakdown and resynthesis of collagen must be important in maintaining
the extracellular matrix; otherwise, vitamin C deficiency in adults would not
cause scurvy, which is characterized by a progressive weakening of connective
tissue due to inadequate hydroxylation of collagen.
19–78 The elasticity of elastin derives from its high content of a helices, which act
as molecular springs.
19–79 In humans, all forms of fibronectin are produced from one large gene by
alternative splicing.
THE PLANT CELL WALL
TERMS TO LEARN
cellulose microfibril primary cell wall
cross-linking glycan secondary cell wall
lignin turgor pressure
pectin
DEFINITIONS
Match each definition below with its term from the list above.
19–87 Thin and extensible cell covering on new plant cells that can accommodate
their growth.
19–88 Bundle of about 40, long, linear chains of covalently linked glucose residues,
all with the same polarity, organized in an overlapping parallel array.
19–89 The large internal hydrostatic pressure that develops in plant cells due to the
osmotic imbalance between the cell interior and the fluid in the plant cell
wall.
19–90 A complex network of phenolic compounds that is an abundant polymer in
secondary cell walls.
19–91 Rigid cell covering laid down in layers inside the initial covering once cell
growth has stopped.
TRUE/FALSE
Decide whether each of these statements is true or false, and then explain why.
19–92 Each cell wall consists of a thin, semirigid primary cell wall adjacent to the
cell membrane and a thicker, more rigid secondary cell wall outside the primary
wall.
19–93 Turgor pressure is the main driving force for cell expansion during growth,
and it provides much of the mechanical rigidity of living plant tissues.
19–94 Unlike the extracellular matrix of animal cells, which contains a large
amount of protein, plant cell walls are composed entirely of polysaccharides.
19–95 If the entire cortical array of microtubules were disassembled by drug treatment,
new cellulose microfibrils would be laid down in random orientations.