#Question id: 1380
#Unit 4. Cell Communication and Cell Signaling
Which of the following apply to the synthesis of plant cell walls? Please select all that apply.
a) Cellulose microfibrils are formed by cellulose synthase complexes called rosettes
b) Cellulose is synthesized using cytoplasmic ATP-glucose and deposited as microfibrils directly on the outer surface of the plasma membrane.
c) Matrix polysaccharides of plant cell walls are synthesized in the Golgi apparatus and exported to the cell wall by endocytosis.
d) The direction of cellulose microfibril growth is determined by the orientation of arrays of microtubules lying just below the plasma membrane.
#Question id: 1381
#Unit 4. Cell Communication and Cell Signaling
Match each definition with given terms
|
1. Large family of structurally related, secreted, dimeric proteins that act as hormones and local mediators to control a wide range of biological functions in all animals. |
A. Rho |
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2. Cell-surface receptor in which the cytoplasmic domain either has enzymatic activity itself or is associated with an intracellular enzyme. |
B. TOR pathway |
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3. A crucial signaling protein in the PI-3-kinase–Akt signaling pathway, so named because it is the target of rapamycin. |
C. Enzyme-coupled receptor |
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4. A kinase that is involved in intracellular signaling pathways activated by cell-surface receptors and that phosphorylates inositol phospholipids at the 3 position of the inositol ring. |
D. Phosphoinositide 3-kinase |
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5. A group of monomeric GTPases that regulate both the actin and microtubule cytoskeletons. |
E. (TGFβ) superfamily |
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6. Cytoplasmic tyrosine kinase present at cell–matrix junctions in association with the cytoplasmic tails of integrins. |
F. Focal Adhesion Kinase |
#Question id: 1382
#Unit 4. Cell Communication and Cell Signaling
Following statements are regarding to cell-cell and cell–extracellular matrix junctions and their adhesion molecules.
A. Adherens junctions and desmosomes are integrin-containing anchoring junctions that bind the membranes of adjacent cells, giving strength and rigidity to the entire tissue.
B. Hemidesmosomes are cadherin-containing anchoring junctions that attach cells to elements of the underlying extracellular matrix.
C. Integrins are a large family of αβ heterodimeric cell-surface proteins that mediate both cell-cell and cell-matrix adhesions and inside-out and outside-in signaling in numerous tissues.
D. Tight junctions block the diffusion of proteins and some lipids in the plane of the plasma membrane, contributing to the polarity of epithelial cells. They also limit and regulate the extracellular (paracellular) flow of water and solutes from one side of the epithelium to the other.
Which of the following statements are incorrect?
#Question id: 1383
#Unit 4. Cell Communication and Cell Signaling
Match the following correctly
#Question id: 1384
#Unit 4. Cell Communication and Cell Signaling
Mutations that block expression of the E-cadherin gene are thought to be an important step in metastasis. To better understand how loss of E-cadherin contributes to metastasis, scientists created two cell lines that differed in their expression of E-cadherin. One cell line expressed normal E-cadherin, but at 10% of the usual levels. The other cell line expressed normal E-cadherin at the usual levels, and also, at high levels a mutant form that included the cytoplasmic domain but lacked the rest of the protein. Both cell lines exhibited strongly reduced cell adhesion in culture. However, only the cell line with reduced expression of normal E-cadherin metastasized when introduced into mice.
Which of the following hypotheses is most consistent with the observations on cell adhesion and metastasis in these cell lines?
#Question id: 1385
#Unit 4. Cell Communication and Cell Signaling
The ability of a population of fibroblasts to migrate along the surface of a tissue culture dish depends on adhesion between the cell surface and the extracellular matrix molecules coating the dish. The dish is coated with laminin, and the only cell-surface protein capable of binding laminin is a cell-adhesion protein called an integrin. Integrins are integral plasma-membrane proteins that function as heterodimers. Under these conditions the rate at which a fibroblast can migrate along the laminin coated culture dish is proportional to the strength of adhesion between the cell and the laminin substrate. The table below lists the rate of cell migration observed for fibroblasts genetically engineered to generate the indicated phenotypes.
Which of the following is the most likely explanation for failure of overexpression of the integrin alpha subunit to alter the rate of fibroblast migration?