Chapter 4: 4.2 Terms + Questions

Which type of junction would be required for cells to communicate? A: gap B: adherens C: hemidesmosome D: tight E: desmosome

A: gap

_____ junctions are anchoring junctions that use cadherins to hold cells together by anchoring to the cells' actin networks. These junctions are found in tissues subject to mechanical stress like the epithelium.

Adherens

Adherens junctions

Adherens junctions help epithelial surfaces resist separation during various contractile activites, as when food moves through the intestines. Consists of plaque, actin, cadherin, and an adhesion belt. Plaque, a dense layer of proteins on the inside of the plasma membrane that attaches both to membrane proteins and to microfilaments of the cytoskeleton. *Adhesion belts* encircle the cell similar to the way a belt encircles your waist. Transmembrane proteins that join the cells are called *cadherins* (a glycoprotein)

Hemidesmosomes

Attach epithelial cells to the basement membrane. They look like half of a desmosome, however the transmembrane glycoproteins are *integrins* (rather than cadherins). On the inside of the plasma membrane, integrins attach to intermediate filaments made up of the protein keratin. On the outside of the plasma membrane, integrins attach to the protein laminin, which is present in the basement membrane. Hemidesmosomes anchor cells not to each other, but the basement membrane.

Which is true of desmosomes? A: They form the adhesion belt, which encircles the entire cell. B: They are associated with intermediate filaments. C: They are formed from connexin membrane proteins. D: They inhibit the passage of molecules between cell membranes.

B: They are associated with intermediate filaments.

Which describes tight junctions? A: attaches cells using cadherins and plaque B: binds cells together with interlocking proteins C: attaches cells to basement membranes D: connects cells through channel proteins

B: binds cells together with interlocking proteins

The epithelial cell junctions that respectively, a) allow the passage of small molecules between adjacent cells, b) restrict the extracellular movement of molecules across epithelium and, c) maintain tissue integrity and strength are _____________. A: desmosomes, tight junctions, and gap junctions B: gap junctions, tight junctions, and desmosomes C: gap junctions, desmosomes, and tight junctions D: tight junctions, desmosomes, and gap junctions E: tight junctions, gap junctions and desmosomes

B: gap junctions, tight junctions, and desmosomes

A gap junction that allows sodium or calcium ions to flow through would have which properties? Select all that apply. A: hydrophilic B: hydrophobic C: nonpolar D: polar

B: hydrophobic C: nonpolar

A gap junction that allows sodium or calcium ions to flow through would have which properties? Select all that apply. A: polar B: nonpolar C: hydrophobic D: hydrophilic

B: nonpolar C: hydrophobic

Heptanol will decrease velocity between cardiac cells in the heart. Which junction does heptanol affect? A: hemidesmosomes B: desmosomes C: gap D: tight E: adherens

C: gap

Gap junctions can be found __________. A: between cells and the basement membrane B: lining the digestive tract C: in cardiac and smooth muscle D: in keratinized stratified squamous

C: in cardiac and smooth muscle

Pemphigus causes blisters because the skin cells cannot firmly attach to each other. Pemphigus is an autoimmune disease that produces antibodies against which strength-producing transmembrane protein? A: laminin B: keratin C: integrin D: plaque

C: integrin

Cell junctions

Contact points between the plasma membranes of tissue cells

Epidermolysis bullosa is a genetic disease where the basale cells of the epidermis cannot successfully attach to the basal of the dermis, resulting in blisters. This attachment occurs primarily due to disruptions in A: desmosome junctions B: gap junctions C: adherens junctions D: hemidesmosome junctions E: tight junctions

D: hemidesmosome junctions

Gap junctions can be found __________. A: in keratinized stratified squamous B: between cells and the basement membrane C: lining the digestive tract D: in cardiac and smooth muscle

D: in cardiac and smooth muscle

Gap junctions are important in smooth muscle. When absent, as in the iris of the eye, what new characteristic does the smooth muscle fibers take on? A: the fibers become incapable of contracting B: the fibers generate more heat energy C: the fibers contract more vigorously D: the fibers contract individually

D: the fibers contract individually

_____ are anchoring junctions that use cadherins to hold cells together. These junctions have a more stable connection because the intermediate filaments anchor two cells together. They are found in tissues that are subject to mechanical stress such as cardiac muscle and the epidermis of the epithelium.

Desmosomes

Ectodermal dysplasia skin fragility syndrome causes impaired wound healing and blistering due to which weak junctions between the cells' keratin? A: hemidesmosomes B: tight C: adherens D: gap E: desmosomes

E: desmosomes

Which junction adheres to lamina? A: gap B: desmosome C: tight D: adherens E: hemidesmosome

E: hemidesmosome

_____ junctions are communicating junctions that use protein channels called connexons to create passageways between cells. Small molecules and ions can pass freely between the cells. These junctions are found in cardiac muscle and some smooth muscles as wells as some nervous tissue.

Gap junctions

Electrical synapses are bidirectional and have no significant synaptic delay. They are formed by _____ junctions.

Gap

_____ are anchoring junctions that use integrins to hold cells to an extracellular matrix. They are found on the basal membrane of epithelial cells, holding them to a basement membrane.

Hemidesmosomes *any time integrins are used, it is hemidesmosome

Tight junctions

Membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid. Cells of epithelial tissue that lines the stomach, intestines, and urinary bladder have many tight junctions.

Desmosomes

Prevent epidermal cells from separating under tension and cardiac muscle cells from pulling apart during contraction. They contain plaque and have cadherins that extend into the intercellular space between adjacent cell membranes and attach cells to one another. Desmosome plaque attaches to elements of the cytoskeleton known as intermediate filaments, which consist of the protein *keratin*. The intermediate filaments extend from desmosomes on one side of the cell across the cytosol to desmosomes on the opposite side of the cell. This arrangement contributes to the stability of the cells and tissue.

Gap junctions

Provide cytoplasmic channels between adjacent animal cells. *Connexins* membrane proteins that form tiny fluid-filled channels (connexons) that connect neighboring cells. Plamsa membranes are not fused together like in tight junctions but are separated by a very narrow intercellular gap. Ions and small molecules can diffuse from the cytosol of one cell to another via connexons, but the passage of large molecules such as vital intracellular proteins is prevented. The transfer of nutrients, and perhaps wastes, takes place through gap junctions in avascular tissues such as the lens and cornea of the eye. Gap junctions allow cells in a tissue to communicate with one another.

The blood-brain barrier (BBB) restricts passage of bacteria and hydrophilic substances. The BBB is formed when endothelial cells in the brain are held together by _____ junctions.

Tight

_____ junction controls barrier functions by restricting diffusion and regulating permeability. Studying movement across this barrier may lead to new therapeutic strategies in drug delivery.

Tight

_____ junctions hold cells together in a sheet, which restricts the movement of substances between the cells. These junctions can be found in cells such as the distal convoluted tubule and collecting duct of the nephron of the kidney.

Tight