Exam 19: Cell Junctions and the Extracellular Matrix

Cellulose is deposited onto the plant cell wall in highly ordered crystalline aggregates by the cellulose synthase complex embedded in the plasma membrane. Would you expect cell wall deposition to continue following treatment of plant cells with a drug that depolymerizes microtubules? Would you expect these cells to be able to switch the orientation of the microfibril pattern between successive lamellae?

Which of the following is NOT an anchoring junction?

What is the most common additional polymer present in the plant secondary, but not primary, cell wall?

Selectins …

This large glycoprotein of the extracellular matrix is associated with elastin fibers and is essential for their integrity. Its deposition in the developing connective tissues often precedes the appearance of elastin. It is part of microfibrils that cover the elastic fibers. This protein is …

EDTA is a metal-ion "chelator" that is commonly used to lower the concentration of free divalent cations in solution. In the lab, your friend has cultured a human cell line on elastic membranes that have been coated with fibronectin and attached to a device that can stretch the membrane. She has quantified the binding of talin to integrin under different conditions, and has presented the results in the following schematic graph, which shows the binding in the presence or absence of EDTA in the cell-culture medium. Which experiment (A or B) do you think was performed in the presence of EDTA? Write down A or B as your answer.

Which of the following is true regarding fibril-associated collagens such as type IX collagen?

Platelets that express a constitutively active Rap1 are able to activate integrins even in the absence of thrombin stimulation. In contrast, cells expressing a binding-deficient version of talin are unable to perform integrin activation. In platelets expressing both of these mutant proteins, what would you expect to observe: the Rap1 gain-of-function phenotype (R) or the talin loss-of-function phenotype (T), as described above? Write down R or T as your answer.

In the following schematic diagram, the estimated attractive or repulsive force between two adhesive cells is plotted as a function of distance between the cells. The dashed curve represents a condition under which the cells express cadherin but not N-CAM. The other two curves represent conditions under which both cadherin and heavily sialylated N-CAM are expressed. In one of the conditions, however, the ionic strength of the medium has been artificially increased by addition of salt. Which curve (1 or 2) do you think represents the high-salt condition? Write down 1 or 2 as your answer.

Overproduction of cadherins such as E-cadherin …

The focal adhesion kinase …

Collagens are extremely rich in …

Which of the following cell junctions uses cadherin cell adhesion molecules to anchor the actin cytoskeleton?

Which collagens are the most common in our body?

Fill in the blank in the following paragraph regarding the extracellular matrix. Do not use abbreviations. "The extracellular matrix of connective tissues in animals is primarily made and secreted by the … family of cells, although they may have more specific names in certain tissues. Being common in connective tissues, these cells can also migrate and proliferate if need be."

Which components of the extracellular matrix are mostly responsible for its ability to resist compressive and tensile forces, respectively?