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Exam 19: Cell Junctions and the Extracellular Matrix

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Question 21

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In the following schematic drawing of connexons as seen from the cytosol of a cell, what is the approximate diameter of each of the pores? Which of the indicated connexons (1 or 2) is more likely to have been incorporated more recently?

A) About 20 nm; connexon 1
B) About 4 nm; connexon 1
C) About 1.5 nm; connexon 1
D) About 4 nm; connexon 2
E) About 1.5 nm; connexon 2

F) All of the above
G) A) and D)

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Question 22

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How is hyaluronic acid different from other glycosaminoglycans of the extracellular matrix?

A) It lacks sulfate groups.
B) It is generally not covalently linked to proteins.
C) It is not assembled in the Golgi apparatus.
D) It can be several megadaltons in mass.
E) All of the above.

F) A) and B)
G) A) and C)

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Question 23

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How does talin activate the inside-out signaling through integrin?

Which of the following extracellular matrix components contains a transmembrane protein?

Multidomain glycoproteins in the extracellular matrix have binding sites for many other macromolecules. These glycoproteins …

Indicate whether each of the following descriptions better applies to cellulose microfibrils (C) or pectins (P) in plant cell walls. Your answer would be a five-letter string composed of letters C and P only, e.g. CPPPP. ( ) It is made into a network by cross-linking glycans. ( ) It is particularly abundant in the middle lamella. ( ) Divalent ions such as calcium can cross-link it to form gels. ( ) It forms more homogeneous polymers. ( ) It contains many negatively charged galacturonic acid units.

Indicate whether each of the following descriptions better applies to glycosaminoglycans (G), fibrous proteins (F), or glycoproteins (P) of the extracellular matrix in animal cells. Your answer would be a six-letter string composed of letters G, F, and P only, e.g. GFPGFP. ( ) They include laminin and fibronectin. ( ) They primarily include collagens. ( ) They include hyaluronan. ( ) They are found in proteoglycans. ( ) They occupy large volumes and form hydrated gels. ( ) They constitute the major proteins of the matrix.

In the following schematic drawings of aggrecan and decorin, which one (1 or 2) corresponds to aggrecan? Which one (1 or 2) is synthesized primarily by chondrocytes in cartilage?

Plasmodesmata in plant cells are functionally similar to animal cells' …

The elasticity of the components of the extracellular matrix can be visualized in a stress-strain curve, in which the tensile stress (corresponding to load) applied to a tissue sample is plotted against the strain (corresponding to deformation) measured in the tissue. In the following stress-strain graph, the elasticity of an intact connective tissue is represented by a dashed curve. The other two curves correspond to the same tissue that has been treated with either formic acid (to digest collagen) or trypsin (to digest elastin). Which curve (1 or 2) do you think corresponds to trypsin treatment?

Indicate true (T) and false (F) statements below regarding integrin signaling. Your answer would be a four-letter string composed of letters T and F only, e.g. TFTT. ( ) Integrins usually bind their ligands with a higher affinity compared to other cell-surface receptors. ( ) Unlike cadherins, integrins usually function as individual dimers and do not cluster. ( ) Anchorage dependence is mainly mediated via integrin signaling. ( ) Integrins can activate the Ras-MAPK pathway.

Which of the following molecules is capable of tension-sensing by exposing binding sites for other proteins when mechanically stretched?

The chemical compound PMA is a potent stimulator of the epithelial-mesenchymal transition in epithelial cells. The activity of two of the following types of proteins is typically up-regulated in epithelial cells treated with PMA, while that of the other two is mainly down-regulated. Choose the two proteins whose activity you think is stimulated by PMA. Your answer would be a two-letter string composed of letters A to D only in alphabetical order, e.g. BC. (A) Cadherin (B) Connexin (C) Matrix metalloprotease (D) Integrin

You have isolated epithelial cells from mouse mammary glands and have grown them in a three-dimensional gelatinous matrix in the presence or absence of a specific inhibitor that targets a transmembrane metalloprotease. The protease is capable of cleaving cadherin near the base of its extracellular domain to release an N-terminal fragment containing the extracellular cadherin domains. The distribution of the cells in the matrix, as seen under a light microscope, one day after the transplantation of the isolated tissue is presented in the following schematic drawings. Which condition (1 or 2) do you think corresponds to the presence of the protease inhibitor? Write down 1 or 2 as your answer.

Type IV collagen molecules can interact at their C-termini to form dimers and at their N-termini to form tetramers. What category do you think this type of collagen belongs to?

The following schematic drawing shows two integrin molecules. Which molecule (a or b) is depicted in its active configuration? Which side of the plasma membrane (1 or 2) represents the cytosol?

Indicate whether each of the following descriptions better applies to connective (C) or epithelial (E) tissues. Your answer would be a four-letter string composed of letters C and E only, e.g. EEEE. ( ) Cells are usually distributed sparsely in the extracellular matrix. ( ) Gap junctions are rarely found. ( ) Direct cell-cell attachments are common. ( ) Cells are tightly associated into sheets.

Malignant cancer cells that have entered the bloodstream can imitate lymphocytes in exiting the bloodstream and entering underlying tissues in the process of metastasis. This "lymphocyte mimicry" can be summarized as …

A researcher has grown monolayers of cells from either of two epithelial cell lines on a permeable supporting membrane that separates two electrolyte chambers. One of the cell lines (A) has been derived from the mammalian kidney and forms epithelial sheets resembling those lining the renal collecting duct and the urinary bladder. The other (B) is derived from the mammalian small intestine. The researcher has measured the voltage (V) and electrical current (I) across the monolayer and has plotted the results in the graph below. Which line (1 or 2) in the graph do you think corresponds to cell line A? Recall that current (I) is related to the applied voltage (V) by the equation I = V/R, in which R is the electrical resistance. Write down 1 or 2 as your answer.

In the following schematic diagram of a simple columnar epithelium lining the digestive tract, indicate which position (A to F) along the basal-apical axis better corresponds to each of the following features. Your answer would be a six-letter string composed of letters A to F only, e.g. FEDABC. ( ) Basal lamina ( ) Cell apex ( ) Adherens junctions ( ) Gap junctions ( ) Hemidesmosomes ( ) Tight junctions