Mastering Ch. 15

In many people, the ingestion of ethanol produces a dose-dependent leakage of interstitial fluid from the intestinal wall into the lumen of the intestine, giving rise to diarrhea. Which of the following proteins is likely inhibited or compromised in function to produce this ethanol-induced diarrhea?

claudins

long fibers of protein found in extracellular matrix that provides structural support for cells

collagen

Indicate whether each of the following proteins or structures is a component of adherens juctions, desmosomes, tight junctions, gap junctions, or plasmodesmata.: Desmocollins

desmosomes

Indicate whether each of the following proteins or structures is a component of adherens juctions, desmosomes, tight junctions, gap junctions, or plasmodesmata.: desmoplankin

desmosomes

The primary role of _____ is to bind animal cells together.

desmosomes

membrane protein complexes that strengthen the adhesion between adjacent cells, like rivets, to protects against pulling forces

desmosomes

Which of the following aspects of collagen would be directly affected by a defect in procollagen peptidase?

extracellular assembly

You discover a dog suffering from an autoimmune response. On further investigation, you find that the cells of various tissues are loosely arranged and do not have characteristic shapes, and the animal is prone to hemorrhaging because of poor blood clotting. Based on these results, the target of the autoimmune response is most likely to be:

fibronectins

role each protein plays in the junction: connexin

forms channels (cytoplasmic connections) between adjacent animal cells

_____ aid in the coordination of the activities of adjacent animal cells.

gap (communicating) junctions

role each protein plays in the junction: Claudins

binds adjoining cells together, creating fused ridges

Explain how the various domains of the fibronectin molecule or the laminin molecule are important for their function?: Laminin

A collagen IV binding site allows it to be attached to the basal laminae (where the molecule is predominantly found) it has an integrin-binding site specific for _6_1 integrins It has multiple domains that allow to attach to other ECM proteins

Choose all the statements below that are true for tight junctions: A) Sites of membrane fusion that are limited to abutting ridges of adjacent membranes B) Require connexons C) seal membranes of two adjacent cells tightly together D) allow the exchange of metabolites between the cytosols of two adjacent cells

A, C

Which of the following experimental data would support the hypothesis that gap junction function in cardiomyocytes (heart muscle cells) is dependent on the gap junction proteins being phosphorylated?

Addition of phosphatase inhibitors to cultures of heart muscle cells results in the cells not beating together, and is correlated to connexin proteins no longer being phosphorylated.

________ surface is the surfaces of intestinal epithelial cells that face the lumen of the intestine. ________ surface is the surfaces of intestinal epithelial cells that face the circulatory system.

Apical surface is the surfaces of intestinal epithelial cells that face the lumen of the intestine. basolateral surface is the surfaces of intestinal epithelial cells that face the circulatory system.

Adhesion junction:

Associated with filaments that confers either contractile or tensile properties.

You suspect that an elderly patient's skin blistering is caused by an autoimmune disorder. If you are correct, the patient's serum likely contains antibodies directed against

BPAG2

______ is responsible for the strength of the ECM, whereas ______ imparts elasticity and flexibility to the ECM.

Collagen is responsible for the strength of the ECM, whereas elastin imparts elasticity and flexibility to the ECM.

_________ occur widely throughout supporting tissues and body fluids, whereas _________ are found mainly in the basal laminae

Fibronectins occur widely throughout supporting tissues and body fluids, whereas laminins are found mainly in the basal laminae

Scurvy is a disease that until the nineteenth century was common among sailors and others whose diets were deficient in vitamin C (ascorbic acid). Individuals with scurvy suffer from various disorders, including extensive bruising, hemorrhages, and breakdown of supporting tissues. Ascorbic acid serves as a reducing agent responsible for maintaining the activity of prolyl hydroxylase, the enzyme that catalyzes hydroxylation of proline residues within the collagen triple helix, which is required for helix stability.: Can you guess why sailors are no longer susceptible to scurvy?

Fresh fruits (vitamin C source) are available now.

Scurvy is a disease that until the nineteenth century was common among sailors and others whose diets were deficient in vitamin C (ascorbic acid). Individuals with scurvy suffer from various disorders, including extensive bruising, hemorrhages, and breakdown of supporting tissues. Ascorbic acid serves as a reducing agent responsible for maintaining the activity of prolyl hydroxylase, the enzyme that catalyzes hydroxylation of proline residues within the collagen triple helix, which is required for helix stability.: Based on this information, postulate a role for hydroxyproline in collagen triple helices.

Hydroxylated proline residues, but apparently not non-hydroxylated proline residues, but apparently not unhydroxylated proline residues, stabilize the collagen triple helix. The hydroxyl groups of this amino acid form interchain hydrogen bonds that help stabilize the assembled triple-stranded helix.

Normally, the positively charged amino acids near the tip of the _______ cause electrostatic _________ of Na+ ions, which leads to ___ paracellular permeability through the ______________. When these amino acids are changed to negatively charged amino acids, this _________ is abolished, allowing the Na+ ions to pass ____ easily through the ____________ via paracellular permeability.

Normally, the positively charged amino acids near the tip of the claudin cause electrostatic repulsion of Na+ ions, which leads to low paracellular permeability through the tight junction. When these amino acids are changed to negatively charged amino acids, this repulsion is abolished, allowing the Na+ ions to pass more easily through the tight junction via paracellular permeability.

Gap junctions:

Require the alignment of connexions in the plasma membranes of two adjacent cells. Allow the exchange of metabolites between the cytoplasms of two adjacent cells.

Tight Junction:

Seal membranes of two adjacent cells tightly together. Sites of membrane fusion are limited to abutting ridges of adjacent membranes.

What can you conclude about gap junctions from each of the following experiments?: Loewenstein and colleagues injected cells with fluorescent molecules of different molecular weights, and a fluorescence microscope was then used to observe the movement of the molecules into adjacent cells. When molecules with molecular weight of 1926 were injected, they did not pass from cell to cell, but molecules with molecular weight of 1158 did.

The gap junctions that connect adjacent cells in insect salivary glands allow the passage of small molecules (molecular weight up to at least 1158 daltons), whereas larger molecules (1926 daltons) do not flow between cells.

The ______ is a carbohydrate-rich zone juxtaposed between the plasma membrane and the ______ of many types of animal cells.

The glycocalyx is a carbohydrate-rich zone juxtaposed between the plasma membrane and the ECM of many types of animal cells.

The groups mediate cell-cell recognition and adhesion; the two groups of proteins can be distinguished from each other functionally because of the calcium requirement of _________ but not ______.

The groups mediate cell-cell recognition and adhesion; the two groups of proteins can be distinguished from each other functionally because of the calcium requirement of cadherins but not IgSFs.

What can you conclude about gap junctions from each of the following experiments?: Microglia (support cells in the brain) are connected by gap junctions. When the fluorescent dye Lucifer yellow is injected into individual microglia that are part of a large group of cells, dye passes to other cells. When microglia are treated with the calcium ionophore, 4Br-A23187, there is a dramatic decrease in dye passage between cells.

The passage of molecules between cells can be regulated by the intracellular Ca2+ content. When the Ca2+ concentration is increased in an individual cell, the movement of fluorescent molecules from that cell is inhibited, suggesting that gap junctions are closed under these conditions.

Scurvy is a disease that until the nineteenth century was common among sailors and others whose diets were deficient in vitamin C (ascorbic acid). Individuals with scurvy suffer from various disorders, including extensive bruising, hemorrhages, and breakdown of supporting tissues. Ascorbic acid serves as a reducing agent responsible for maintaining the activity of prolyl hydroxylase, the enzyme that catalyzes hydroxylation of proline residues within the collagen triple helix, which is required for helix stability.: Construct the sequence of events leading from a dietary vitamin C deficiency to symptoms such as bruising and breakdown of supporting tissues.

The sequence of events from the first to the last in the dficiency of Vit-C: 1. Tissue levels of ascorbic acid is low 2. Enzyme prolyl hydroxylase is inactive 3. Proline is not hydroxylated 4. The triple helix is inadequately stabilized 5. Collagen breaks down 6. Defects in tissues that depend on collagen 7. Tissues that depend on collagen are subject to breakdown and bruise.

Scurvy is a disease that until the nineteenth century was common among sailors and others whose diets were deficient in vitamin C (ascorbic acid). Individuals with scurvy suffer from various disorders, including extensive bruising, hemorrhages, and breakdown of supporting tissues. Ascorbic acid serves as a reducing agent responsible for maintaining the activity of prolyl hydroxylase, the enzyme that catalyzes hydroxylation of proline residues within the collagen triple helix, which is required for helix stability.: Why do you think British sailors are called "limeys" to this day?

The term reflects the British Navy's use of limes.

These are transmembrane proteins that serve as receptors for ECM proteins such as collagen, fibronectin, and laminin; _________ is the best-characterized _________.

These are transmembrane proteins that serve as receptors for ECM proteins such as collagen, fibronectin, and laminin; selectin is the best-characterized integrin.

Historically, an important strategy for disrupting the adhesion of integrins to their ligands is by using a synthetic peptide that mimics the binding site on the ECM molecule to which the integrin attaches. In the case of fibronectin, the amino acid sequence is arginine-glycine-aspartate (when written using the single letter designation for each amino acid, this sequence becomes RGD). Explain why addition of such synthetic peptides would disrupt binding of cells to their normal substratum.

When the integrins are bound to RGD peptides, their receptors will be unavailable for binding to FN (or LN), and thus cells will be inhibited from binding to the ECM.

Which of the following experimental treatments would NOT be a potentially effective strategy to inhibit or prevent cell-cell adhesion?

adding an antagonist to prevent integrin function

Indicate whether each of the following proteins or structures is a component of adherens juctions, desmosomes, tight junctions, gap junctions, or plasmodesmata.: α-Catenin

adherens junction

Indicate whether each of the following proteins or structures is a component of adherens juctions, desmosomes, tight junctions, gap junctions, or plasmodesmata.: E-cadherin

adherens junctions

role each protein plays in the junction: α-Catenin

anchors actin microfilaments to the plasma membrane

Indicate whether each of the following proteins or structures is a component of adherens juctions, desmosomes, tight junctions, gap junctions, or plasmodesmata.: Connexin

gap junctions

small channels that form across the plasma membrane of adjacent cells; especially important in intercellular communication

gap junctions

Mice lacking plakoglobin have skin defects but usually die from

heart failure

Explain how the various domains of the fibronectin molecule or the laminin molecule are important for their function?: Fibronectin

it can bind to fibrin (important during blood clot formation) and can bind to collagen or heparin sulfate proteoglycans for attaching it to the ECM. the RGD-containing cell-binding is crucial for allowing cells to attach to this molecule, because this is the site that is bound by integrins to the cell surface It has multiple domains that allow to attach to other ECM proteins

For a cancerous tumor to move from tissue to tissue in metastasis, which proteins of the basal lamina must it be able to degrade or pass through?

laminins and type IV collagen

Which of the following could you use experimentally to help you determine which carbohydrates are present on a cell's surface?

lectins

role each protein plays in the junction: desomoplakin

major proteins of the desmosome plaque

An autoimmune disorder in which an immune response targets Type V collagen fibers is most likely to affect the

skin

role each protein plays in the junction: desmocollins

the desmosomal cadherins that probably bind the plasma membranes of the two cells together

Indicate whether each of the following proteins or structures is a component of adherens juctions, desmosomes, tight junctions, gap junctions, or plasmodesmata.: Claudins

tight junctions

Which of these cell junctions form a barrier to the passage of materials?

tight junctions

membrane proteins that create a water tight seal between cells

tight junctions

role each protein plays in the junction: E-cadherin

transmembrane adhesive connections between two adjacent animal cells