2.2

Question 1

These surfaces contain specialized junctions that provide adhesion between cells and restrict movement of materials into and out of lumina.

Answer 1

Lateral Epithelial Surfaces

Question 2

Lateral Epithelial Surfaces

Answer 2

• Junctional Complex
• Gap Junctions
• Lateral interdigitations

Question 3

The __________ is an intricate arrangement of membrane-associated structures that functions in cell-to-cell attachment of columnar epithelial cells. It corresponds to the terminal bar observed in epithelia by light microscopy and consists of three distinct components that are visible by electron microscopy.

Answer 3

Junctional complex

Question 4

Junctional Complex

The _________________ is a zone that surrounds the entire apical perimeter of adjacent cells and is formed by fusion of the outer leaflets of the cells’ plasma membranes

Answer 4

Tight Junction (zonula occludens)

Question 5

The tight junction (zonula occludens) is a zone that surrounds the entire apical perimeter of adjacent cells and is formed by _______________ of the cells’ plasma membranes.

Answer 5

Fusion of the outer leaflets

Question 6

Tight junction (zonula occludens)

Answer 6

a. In freeze-fracture preparations of this zone, the tight junction is visible as a branching anastomosing network of intramembrane strands on the plasma membrane inner leaflet next to the cytoplasm (P-face) and grooves on the corresponding external E-face, the inner aspect of the outer leaflet. The strands consist of transmembrane proteins of each cell attached directly to one another, thus sealing off the intercellular space.

b. The tight junction prevents movement of substances into the intercellular space from the lumen. This ability (its tightness) is directly related to the number and complexity of the intramembrane strands.

c. The tight junction is analogous to the fascia occludens, a ribbonlike area of fusion between transmembrane proteins on adjacent endothelial cells lining capillaries.

Question 7

Tight junction:

In freeze-fracture preparations of this zone, the tight junction is visible as a branching anastomosing network of ______________ on the plasma membrane inner leaflet next to the cytoplasm (P-face) and _________on the corresponding external E-face, the inner aspect of the outer leaflet. The strands consist of _______________ of each cell attached directly to one another, thus sealing off the intercellular space.

Answer 7

Intramembrane strands; Grooves; Transmembrane proteins;

Question 8

Tight junction:

The tight junction prevents movement of substances into the intercellular space from the lumen. This ability (its tightness) is directly related to the number and complexity of the __________________.

Answer 8

Intramembrane strands

Question 9

Tight junction:

The tight junction is analogous to the _________________, a ribbonlike area of fusion between transmembrane proteins on adjacent ____________ lining capillaries.

Answer 9

Fascia occludens; Endothelial cells

Question 10

The _________________ is the zone that surrounds the entire perimeter of epithelial cells just basal to the tight junction.

Answer 10

Intermediate junction (belt desmosome; zonula adherens)

Question 11

Intermediate junction (belt desmosome; zonula adherens)

Answer 11

a. It is characterized by a 10- to 20-nm separation between the adjacent plasma membranes, where the extracellular portions of cadherin molecules occupy the intercellular space.

b. A mat of actin filaments is located on each of its cytoplasmic surfaces. The actin filaments are linked, via _-actinin and vinculin, to the transmembrane glycoprotein E-cadherin. This protein is markedly dependent on calcium ions for promoting adhesion at this structurally supportive junction.

c. It is analogous to the fascia adherens, a ribbonlike adhesion zone in the intercalated disks of cardiac muscle.

Question 12

Intermediate junction (belt desmosome; zonula adherens):

It is characterized by a _________-nm separation between the adjacent plasma membranes, where the extracellular portions of cadherin molecules occupy the intercellular space

Answer 12

10- to 20

Question 13

Intermediate junction (belt desmosome; zonula adherens):

A mat of __________ is located on each of its cytoplasmic surfaces. The actin filaments are linked, via _-actinin and vinculin, to the transmembrane glycoprotein ____________ . This protein is markedly dependent on calcium ions for promoting _________at this structurally supportive junction

Answer 13

Actin filaments; E-cadherin; Adhesion

Question 14

Intermediate junction (belt desmosome; zonula adherens):

It is analogous to the __________, a ribbonlike adhesion zone in the ____________________ of cardiac muscle.

Answer 14

Fascia adherens; Intercalated disks

Question 15

A ____________ is a small, discrete, disk-shaped adhesive site. It is also commonly found at sites other than the junctional complex, where it joins epithelial cells.

Answer 15

Desmosome (macula adherens)

Question 16

Desmosome (macula adherens)

Answer 16

a. It is characterized by a dense plaque of intracellular attachment proteins, called desmoplakins, on the cytoplasmic surface of each opposing cell.

b. Keratin intermediate filaments in bundles (tonofilaments) loop into and out of the dense plaque from the cytoplasm.

c. Between the adjacent cells are transmembrane linker glycoproteins, called desmogleins and desmocollins, that are cadherin molecules.

Question 17

Desmosome (macula adherens):

It is characterized by a ____________ of intracellular attachment proteins, called ________________, on the cytoplasmic surface of each opposing cell.

Answer 17

Dense plaque; desmoplakins

Question 18

Desmosome (macula adherens):

_________intermediate filaments in bundles (tonofilaments) loop into and out of the dense plaque from the cytoplasm.

Answer 18

Keratin

Question 19

Desmosome (macula adherens):

Between the adjacent cells are transmembrane linker glycoproteins, called ________________and _________, that are cadherin molecules.

Answer 19

Desmogleins and desmocollins

Question 20

The ____________ (communicating junction; nexus) is not part of the junctional complex and is common in certain tissues other than epithelia (e.g., central nervous system, cardiac muscle, and smooth muscle).

Answer 20

Gap junction

Question 21

Gap junctions couple adjacent cells ____________ and _____________.

Answer 21

metabolically and electrically

Question 22

The _____________ is a plaque-like entity composed of an ordered array of subunits called connexons, which extend beyond the cell surface into the gap to keep the opposing plasma membranes approximately 2 nm apart.

Answer 22

Gap junction

Question 23

The gap junction is a plaque-like entity composed of an ordered array of subunits called ___________, which extend beyond the cell surface into the gap to keep the opposing plasma membranes approximately ____ nm apart.

Answer 23

Connexons; 2

Question 24

Communicating junction; nexus

Answer 24

Gap junction

Question 25

Gap Junction

Answer 25

a. Connexons consist of six cylindrical subunits (composed of proteins called connexins), which are arranged radially around a central channel with a diameter of 1.5 nm. b. Precise alignment of connexons on adjacent cells produces a junction where cell-to-cell channels permit passage of ions and small molecules with a molecular weight of less than 1,200 d (daltons). c. Connexins may alter their conformation to shut off communication between cells.

Question 26

Gap Junction: _________________ consist of six cylindrical subunits (composed of proteins called connexins), which are arranged radially around a central channel with a diameter of _____ nm.

Answer 26

Connexons; 1.5

Question 27

Gap Junction: Precise alignment of connexons on adjacent cells produces a junction where _____________ channels permit passage of ions and small molecules with a molecular weight of less than _______ d (daltons).

Answer 27

Cell-to-cell; 1,200

Question 28

Gap Junction: ____________may alter their conformation to shut off communication between cells

Answer 28

Connexins

Question 29

________________ are irregular fingerlike projections that interlock adjacent epithelial cells.

Answer 29

Lateral interdigitations