Test 3. Lecture 30

Question 1

___________ is the most abundant type.
It forms collagen fibrils in which the triple helical molecules form regular
staggered arrays.
Assembly of fibrils occurs outside the cell from soluble precursor procollagens.

Answer 1

Type I collagen

Question 2

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

Answer 2

lysine

hydroxylysine

Question 3

Fibrils can come together to form __________, which can be several
μm in diameter

Answer 3

collagen fibers

Question 4

2. Some types of collagen do not form fibrils.

 Fibril-associated collagens bind to collagen fibrils and link them to one
another and to other matrix components.

3. Basal laminae are mostly _______________, but also _____________. All are
   network-forming collagens.

The Gly-X-Y repeats are interrupted by short nonhelical sequences, making
them more flexible.
They form 2-D cross-linked networks instead of fibrils.

Answer 4

type IV

VI and XVIII

Question 5

Extracellular matrix gels are formed from polysaccharides called
_______________.
GAGs are repeating units of disaccharides.
Except for hyaluronan, the sugars are modified with sulfate groups.

Answer 5

glycosaminoglycans (GAGs)

Question 6

1. The addition of sulfate groups make GAGs
   highly negatively charged.
   They bind positively charged ions and trap
   water molecules to form hydrated gels.

2.___________ is the only GAG that is a
single long polysaccharide chain.
It is synthesized at the plasma membrane
by a transmembrane hyaluronan synthase.

3. All of the other GAGs are linked to proteins
   to form _____________

Proteoglycans interact with ___________ to
form large complexes in the extracellular
matrix.

_________, the major proteoglycan of
cartilage, has about 100 chains of
chondroitin sulfate attached to a core
protein

Answer 6

Hyaluronan

proteoglycans.

hyaluronan

Aggrecan

Question 7

Matrix adhesion proteins link matrix components to one another and to cell
surfaces.

___________ is the main adhesion protein of connective tissues, which is often
cross-linked into fibrils.
It has binding sites for both _____________

Answer 7

Fibronectin

collagen and GAGs.

Question 8

1. Basal laminae contain adhesion proteins of the ___________ family.
   They consist of three polypeptide chains, each with rod-like domains with
   interspersed globular domains.
2. The subunits have binding sites for different receptors.
3. Laminins can self-assemble into networks.

Answer 8

laminin

Question 9

Laminins are tightly associated with __________, an adhesion protein that also binds
to type IV collagen

As a result of multiple interactions, ________________________
form cross-linked networks within basal laminae.

Answer 9

nidogenlaminin,

nidogen, collagen, and proteoglycans

Question 10

_________ are cell surface receptors that attach
cells to the extracellular matrix.

They are heterodimers; different combinations
of subunits result in 24 different integrins.

Integrins bind to various components of the
extracellular matrix, including _________,
___________, and ________-

Answer 10

Integrins

collagen, fibronectin, and laminin

Question 11

Integrins also anchor the cytoskeleton to the extracellular matrix.
Two types of cell-matrix junctions:

1. ______________: bundles of ___________ are anchored to β subunits of
   integrins via other proteins: α-actinin, talin, and vinculin.
2. __________ anchor epithelial cells to basal laminae.
   α6β4 integrins link basal lamina layer of the extracellular matrix to ____________ via plectin.
   α6β4
   integrins also bind to laminins

Answer 11

Focal adhesions
actin filaments

Hemidesmosomes
intermediate filaments

Question 12

Integrins were first identified by ____________ and ___________
microscopy of transmembrane glycoproteins at points of cell adhesion to
the matrix.
The scientists were then able to isolate a molecular clone encoding one of
these glycoproteins (integrin) from a cDNA library of chick embryo
fibroblasts.

Answer 12

immunofluorescence and immunoelectron

Question 13

Focal adhesions can be ______________ or turn over rapidly as cells move.

Integrins can reversibly bind matrix components, due to their ability to change
conformation between active and inactive states.

Answer 13

stable

Question 14

Focal adhesions develop from small clusters of integrins (__________________) by sequential recruitment of formin, which initiates actin
bundle formation, talin, vinculin, and α-actinin.

Answer 14

focal

complexes

Question 15

Animal cells MODIFY THE EXTRACELLULAR MATRIX via enzymes that modify
___________ and proteases that digest collagen.

The __________digest a variety of matrix proteins, including
collagens, laminin, and perlecan, cell surface receptors, and adhesion
molecules

Answer 15

glycosaminoglycans
proteases that digest collagen.

metalloproteases

Question 16

Interactions between cells are critical for development and function of
multicellular organisms.

Some cell-cell interactions are transient; others are stable and play a key
role in the organization of tissues.

Some types of junctions allow rapid communication between cells.
Cell-cell adhesion is mediated by four groups of ____________
– Selectins
– Integrins
– Immunoglobulin (Ig) superfamily
– Cadherins

Many adhesions depend on divalent
cations, requiring Ca2+, Mg2+ or Mn2+
.

Answer 16

cell adhesion molecules

Question 17

what are the four cell adhesion molecules that mediate cell-cell adhesion?

Answer 17

– Selectins

– Integrins

– Immunoglobulin (Ig) superfamily

– Cadherins

Question 18

1.______________mediate transient interactions between LEUKOCYTES and
ENDOTHELIA CELLS OR BLOOD PLATELETS

Leukocytes leave the circulation at sites of tissue inflammation by
interacting with the endothelial cells of capillaries.

The selectins bind to oligosaccharide ligands on endothelial cells.

2. This is followed by more stable interactions between LEUKOCYTE INTEGRINS AND INTERCELLULAR ADHESION MOLECULES (ICAMs, members of the Ig
   superfamily) on endothelial cells.

Answer 18

Selectins

Question 19

BINDING OF ICAMS TO INTEGRINS is an example of a __________________:
An adhesion molecule on one cell recognizes a different molecule on
another cell.

Answer 19

heterophilic interaction:

Question 20

_____________: an adhesion molecule on one cell binds to the

same molecule on another cell.

Answer 20

Homophilic interactions

Question 21

Homophilic binding between neural cell adhesion molecules (N-CAMs)
contributes to associations between nerve cells during development.

___________ MEDIATE HOMOPHILLIC INTERACTIONS

Answer 21

Cadherins

Question 22

Stable adhesion junctions linking the cytoskeletons of adjacent cells are
usually based on cadherins:

Answer 22

– adherens junctions

– Desmosomes

Question 23

____________ link actin
filaments of adjacent cells.
Includes β-catenin, p120, and α-
catenin, cla

Answer 23

Adherens junctions

Question 24

β-catenin and p120 are members of
the ________________.
They bind to cadherin and help
maintain stability.

Answer 24

armadillo protein family

Question 25

______________link the intermediate
filament cytoskeletons of
adjacent cells.

Answer 25

Desmosomes

Question 26

____________ and _________
(transmembrane cadherins) bind
by heterophilic interactions
across the junction.

Answer 26

Desmoglein and desmocollin

Question 27

____________ and ______- bind to
the cadherins and link to the
intermediate filament binding
protein, desmoplakin.

Answer 27

Plakoglobin and plakophilin

Question 28

____________ in epithelial cell
sheets form a seal that prevents
free passage of molecules and
ions between cells

They also separate apical and
basolateral domains of the plasma
membrane by preventing the free
diffusion of lipids and membrane
proteins.

Answer 28

Tight junctions

Question 29

Tight junctions provide minimal
adhesive strength between the
cells, so they are usually
associated with ADHERENS
JUNCTIONS and DESMOSOMES in a
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Answer 29

junctional complex

Question 30

Tight junctions are formed by a network of protein strands that continues
around the entire cell.

Transmembrane proteins in the network are \_\_\_\_\_\_\_\_\_\_\_,\_\_\_\_\_\_\_\_\_, and \_\_\_\_\_\_\_\_\_
adhesion molecule (JAM).

The cytosolic tails bind with zonula occludens proteins, which link to the
actin cytoskeleton.

Answer 30

occludin, claudin, and junctional