BIO 127 Chapter IIIB: Cell Junctions

seal between epithelial cells

cell junctions

what are the three functional groups of cell junctions and their subtypes

occluding junctions, communicating junctions, and anchoring junctions

type of occluding junctions that are found in vertebrates only

tight junctions

type of occluding junctions that are found in invertebrates mainly

septate junction

three types of communicating junctions

gap junctions, chemical synapses, and plasmodesmata

type of communciating junctions found in plants

plasmodesmata

two types of anchoring junctions and their attachment sites

actin filaments = adherens junctions and focal adhesions

intermediate filaments = desmosomes and hemi-desmosomes

tight junctions are also known as

zonulae occludens

anastomosing network of protein strands connecting the outer leaflets of two interacting plasma membranes

tight junctions

junctions that encircle the apical end of each cell in the epithelial sheet

tight junctions

opening or connection between two things that are normally diverging or branching, such as between veins, blood vessels, leaf veins

anastomosing

6 proteins involved in tight junctions

occludin, claudin, zonulae occludens proteins, cingulin, junctional adhesion molecules (JAM), cadherins

[tight junction proteins] important in tight junction stability and barrier function

occludin

[tight junction proteins] determines the barrier properties of cell to cell contact existing between sealed PMs

claudin

[tight junction proteins] serve as scaffolding proteins and provide structural basis for the assembly of multiprotein complexes at the cytoplasmic surface of intercellular junctions

ZO proteins

[tight junction proteins] involved in regulating gene expressions or behavior of endothelial or epithelial cells

cingulin

[tight junction proteins] mediates interaction between two cells

jam

[tight junction proteins] mediate cell to cell adhesion in animals

cadherins

[tight junction proteins] play a crucial role in tissue morphogenesis and homeostasis by regulating contact formation and stability

cadherins

two functions of tight juncitons

(1) seal neighboring cells together so that water soluble molecules cannot leak between cells, (2) confine transport proteins to their appropriate membrane domains

in which cells are the sealing function of tight junctions observed

in epithelia of intestine and urinary bladder

[occluding cell junctions] allow epithelia to serve as barriers to solute diffusion

tight junctions

[occluding cell junctions] prevent the transport of tracer molecules into the cell

tight junctions

what happens at the apical domain during transcellular transport of glucose

Na+-driven glucose symport actively transports glucose into the epithelial cell

what happens at the basolateral domain during transcellular transport of glucose

glucose carriers mediate the facilitated diffusion of glucose from the cell to the extracellular fluid

what is the function of the tight junction to the transcellular transport of glucose

maintains the directional transport of glucose by serving as a seal that does not allow the Na+-driven glucose symport to migrate to the basolateral domnain of the cell

[occluding cell junctions] form a continuous band around the apical borders of epithelial cells

septate junctions

septate junctions are arranged in _________ with regular periodicity

parallel rows

septate junctions are the main occluding junction in these types of animal tissues

invertebrate tissues

septate junctions coexist with

adhesion belts

[occluding cell junctions] serve as sites of attachment for actin filaments to hold cells together

occluding junctions

[communicating junctions] most widespread type of junction and is present in high number in animals

gap junction

where the gap junctions are found

under the extracellular matrix

the membranes of adjacent cells are separated by a uniform gap junction of __________ distance

2-4 nm distancew

the gap in gap junctions is spanned by

channel proteins or connexins

each channel has _______ connexons and each connexon has ______ connexins

2; 6

structures in gap junctions that protrude from the cell surface and hold interacting plasma membranes at a fixed distance

gap junctions

the gap junctions close when the Ca2+ concentration ____________ and the pH _______ in the cytosol

increases; decreases

five functions of gap junctions

Cupcakke Everyday CPR

1. cell-cell communication

2. electrical and chemical coupling between cells in contact

3. coordination of activities of individual cells

4. passageway of intracellular mediators

5. role in embryogenesis

arrange the following molecules based on how easy it is for them to pass through gap junctions, from easiest to hardest

sugars, amino acids, small molecules, inorganic ions

1. small molecules

2. inorganic ions

3. sugars

4. amino acids

function of gapjunctions for nerve cells

spread action potential in nerve cells

function of gap junctions for heart and smooth muscles

help synchronize contraction of the heart and smooth muscles

function of gap junctions for the intestine

help in the peristaltic movement of the intestine

in the epithelial cell sheet, the gap junction helps with

coordinating the beating of the individual cilia

during the early vertebrate embryo or the late 8-cell stage, cells are ___________ to one another as a function of gap junctions

electrically coupled

[communicating junctions] use chemical messengers such as neurotransmitters to send signals to neurons

chemical synapses

[communicating junctions] junctions found in plant cells that function for direct cell-cell communication

plasmodesmata

[communicating junctions] connects the cytoplasm of adjacent cells

plasmodesmata

a narrow, cylindrical tube that runs through the center of the plasmodesmata channel that is continuous with smooth ER elements

desmotubule

molecules with MW _______ are allowed to pass through plasmodesmata

<800 daltons

junctions that connect the cytoskeleton of a cell to those of its neighboring cells or to the extracellular matrix

anchoring junctions

anchoring junctions are abundant in tissues subjected regularly to severe ______

mechanical stress

serve as attachment sites of actin filaments in anchoring junctions

adherens junctions

adherens junctions found in adhesion belts

cell-cell adherens junctions

adherens junctions found in focal contacts

cell-matrox adherens junctions

two types of anchoring junctions that serve as attachment sites of intermediate filaments

desmosomes (cell-cell) and hemidesmosomes (cell-matrix)

[classes of proteins in anchoring junctions] form a distinct plaque on the cytoplasmic side of the plasma membran

intracellular attachment proteins

[classes of proteins in anchoring junctions] connect functional complex to actin filaments or intermediate filaments

intracellular attachment proteins

area where transmembrane linker proteins bind to one or more intracellular attachment proteins

cytoplasmic domain

area where transmembrane linker proteins interact with the extracellular matrix and extracellular domains of a transmembrane linker protein on another cell

extracellular domain

[anchoring junctions] connect bundles of actin filaments from cell to cell or cell to ECM

adherens junctions

form a continuous adhesion belt or zonula adherin in epithelial cells of small intestine

cell-cell adherens junctions

attached to actin filaments via a set of intracellular attachment proteins

cadherin

connect actin filaments with actin filaments

adherens junctions

during migration on cell-matrix adherens junctions, _____ or ______ are formed

focal contacts or adhesion plaques

transmembrane linker protein in focal contacts

integrin

intracellular attachment proteins in anchoring junctions

talin, a-actinin, vinculin

establish actin filament to extracellular matrix connection

cell-matrix adherens junctions

type of filaments found in desmosomes for epithelial cells

keratin filaments

type of filaments found in desmosomes for heart muscle cells

dermin filaments

desmosomes are composed of intracellular attachment proteins such as

plakoglobin and desmo plakin

desmosomes are a requirekment to prevent the _______ of nerve cell axons

rupture

resemble desmosomes morphologically but are both functionally and chemicaqlly distinct

hemidesmosomes

hemidesmosomes connect the _______ of epithelial cells to the basal lamina

basal surface

transmembrane linker proteins in focal contacts

integrins