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Cell Biology > ch.16 > Flashcards

ch.16 Flashcards

1
Q

Where are most animal cells embedded?

A

in an extracellular matrix

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2
Q

What are basal laminae?

A

thin layers on which epithelial cells rest

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3
Q

What do basal laminae surround?

A

muscle cells, adipose cells, and peripheral nerves

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4
Q

Where is extracellular matrix most abundant?

A

in connective tissues

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5
Q

Bone, tendon, and cartilage is considered ____ tissue.

A

connective

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6
Q

What do extracellular matrices have?

A

tough fibrous proteins embedded in a gel-like polysaccharides

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7
Q

What do adhesion proteins do?

A

link components of the matrix to one another and to attached cells

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8
Q

tendons have high proportion of _____ _______

A

fibrous proteins

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9
Q

cartilage has high level of _______ that form a compression-resistant gel.

A

polysaccharides

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10
Q

Bone matrix is hardened by what?

A

calcium phosphate crystals

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11
Q

What is the major structural protein?

A

collagen

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12
Q

What does collagen form?

A

triple helicies

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13
Q

Three polypeptide chains are wound together to form _______

A

collagen

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14
Q

What do the triple helix domains consist of?

A

repeats of the amino acid sequences Gly-X-Y (a glycine in every third position)

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15
Q

what is the smallest amino acid that allows polypeptides to pack closely together?

A

glycine

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16
Q

What amino acid is frequently found in the X position?

A

proline

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17
Q

what is frequently found in the Y position?

A

hydroxyproline

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18
Q

What amino acid stabilizes the helices?

A

hydroxyl groups (by forming hydrogen bonds)

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19
Q

where is hydroxyproline formed?

A

in the ER by modification of proline in collagen polypeptide chains

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20
Q

What is the most abundant type of collagen?

A

type I

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21
Q

What does type I collagen form?

A

collagen fibrils in which the triple helical molecules form regular staggered arrays

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22
Q

Assembly of fibrils occurs outside the cell from soluble precursor _______.

A

procollagens

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23
Q

Covalent cross-links between side chains of _____ and hydroxylysine residues help strengthen the fibrils.

A

lysine

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24
Q

______ can come together to form collagen fibers, which can be several μm in diameter

A

Fibrils

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25
What type of collagen is basal laminae?
type IV
26
Gly-X-Y repeats are interrupted by short nonhelical sequences, making them more ______.
flexible
27
What are 2 other functions of collagen?
1) link some basal laminae to underlying connective tissues 2) participate in cell-matrix interactions
28
Connective tissues with elastic fibers are common where?
in organs that stretch and return to shape (etc. lungs)
29
Elastic fibers are made of ______ which is cross-linked into a network.
elastin
30
Extracellular matrix gels are formed from ______
polysaccharides
31
what are glycosaminoglycans (GAGs)?
repeating units of disaccharides
32
What is hyaluronan?
the only GAG that is a single long polysaccharide chain
33
Where is hyaluronan synthesized?
plasma membrane
34
How is hyaluronan synthesized?
by a transmembrane hyaluronan synthase
35
all other GAGs are linked to proteins to form __________
proteoglycans
36
What is the function of matrix adhesion proteins?
link matrix components to one another and to cell surfaces
37
what is fibronectin?
the main adhesion protein of connective tissues
38
Fibronectin is often cross-linked into ______
fibrils
39
What has binding sites for both collagen and GAGs?
fibronectin
40
what consists of 3 polypeptide chains, each with rod-like domains and interspersed globular domains?
basal laminae
41
Basal laminae subunits have binding sites for surface receptors and _______
proteoglycans
42
Can laminins self-assemble into networks?
yes
43
what are integrins?
transmembrane proteins that attach cells to the extracellular matrix
44
how many different integrins are there?
24
45
what do integrins bind to?
various components of the extracellular matrix, including collagen, fibronectin, and laminin
46
Integrins also anchor the ______ to the extracellular matrix.
cytoskeleton
47
what are the 2 types of cell-matrix junctions?
focal adhesions and hemidesmosomes
48
what are focal adhesions?
bundles of actin filaments anchored to beta subunits of integrins via other proteins
49
what proteins anchor actin filaments to beta subunits of integrins?
alpha-actinin, talin, and vinculin
50
what do hemidesmosomes do?
anchor epithelial cells to basal laminae
51
what links the basal lamina layer of the extracellular matrix to intermediate filaments via plectin?
alpha6 and beta4 integrins
52
What do alpha6 and beta4 integrins also bind to?
laminins
53
what cell adhesion molecules mediate cell-cell adhesion?
selectins, integrins, immunoglobulin (Ig) suer family, and cadherins
54
many cell-cell adhesions depend on divalent cations requiring ____, _____, or _____
Ca2+, Mg2+, or Mn 2+
55
what do selectins specifically mediate?
transient interactions between leukocytes and endothelial cells or blood platelets
56
______ leave the circulation at sites of tissue inflammation by interacting with the endothelial cells of capillaries.
leukocytes
57
What is an example of a heterophilic interaction?
binding of ICAMs to integrins (where an adhesion molecule on one cell recognizes a different molecule on another cell)
58
What are homophilic interactions?
an adhesion molecule on one cell binds to the same molecule on another cell
59
The homophilic binding between N-CAMs contributes to what?
associations between nerve cells during development
60
what mediates homophilic interactions?
cadherins
61
What are 2 stable adhesion junctions linking the cytoskeletons of adjacent cells?
adherens junctions + desmosomes
62
Adherens junctions do what?
link actin filaments of adjacent cells
63
Beta-catenin and p120 are members of the _____ protein family
armadillo
64
What do beta-catenin and p120 do?
bind to cadherin and help maintain stability
65
what do desmosomes do?
link intermediate filament cytoskeletons of adjacent cells
66
What are the 2 cadherins that bind across the junction?
desmoglein + desmocollin
67
Plakoglobin + plakophilin bind to the cadherins and link to _________
desmoplakin
68
desmoplakin binds what?
the intermediate filaments
69
Tight junctions in epithelial cell sheets do what?
form a seal that prevents free passage of molecules and ions between cells
70
What do tight junctions separate?
apical and basolateral domains of the plasma membrane
71
Tight junctions provide minimal _______ ______ between the cells.
adhesive strength
72
Tight junctions are usually associated with what?
adherens junctions and desmosomes in a junctional complex
73
How are tight junctions formed?
by a network of protein strands that continues around the entire cell
74
What are transmembrane proteins in the network?
occuludin, claudin, and junctional adhesion molecules (JAM)
75
What do the cytosolic tails link?
the tight junction complex to the actin cytoskeleton
76
Within a tissue, cells are often linked by _____ ______.
gap junctions
77
In electrically excitable cells, passage of ions through gap junctions couples does what?
synchronizes contractions of neighboring cells
78
Gap junctions also allow passage of _____ _____.
signaling molecules
79
Gap junctions consist of transmembrane proteins in the _______ family
connexin
80
how many connexins form a connexon?
6
81
______ of adjacent cells align, forming open channels between the two cytoplasms.
Connexons
82
Specialized gap junctions occur on some nerve cells and form an _______ _________.
electrical synapse
83
When specialized gap junctions are open, what do they allow?
the rapid passage of ions between the 2 nerve cells
84
Several human diseases are associated with _____ mutations.
connexon
85
Adhesion between plant cells is mediated by the _____ _______.
cell walls
86
The ______ ________, a pectin-rich region, acts as a glue to hold adjacent cells together
middle lamella
87
Adjacent plant cells communicate through cytoplasmic connections called ________
plasmodesmata
88
What does plasmodesmata allow the regulated passage of?
macromolecules and regulatory molecules such as transcription factors
89
______ and ______ can be targeted to plasmodesmata in response to specific signals.
proteins and lipids

Cell Biology (8 decks)

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