Mid-term_1_2021

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Johns Hopkins University *

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580442

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Biology

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Dec 6, 2023

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docx

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Tissue Engineering 580.442 / 580.642 MID-TERM EXAM – 1 (Fall 2021) This is a CLOSED BOOK exam. No notes, lecture slides, or other class materials should be available to you electronically or otherwise. You should be logged into the regular class zoom link with your video on while doing the exam. Question 1 – 9 points Question 4 – 13 points Question 2 – 12 points Question 5 – 11 points Question 3 – 15 points Total = 60 points 1. A flow chamber such as the one shown below may be used to quantify the strength of adhesion of cells to the underlying substrate. Cells are attached to the bottom surfaces and a fluid flows with a laminar profile through the chamber. a. Describe how this system might be used to measure the strength of cell adhesion to the substrate. ( Do NOT include any equations for this explanation – just describe the concepts with the key assumptions that might allow an experimenter to use flow to measure adhesion strength ). ( 4 points ) Since the flow applies pressure onto adherent cells, but not adherent cells, the strength of adhesion can be determined by the detachment tension for adherent cells from the surface of substrate when the fluid flows through the chamber. So if the fluid flow rate is known, we can7 calculate the strength of cell adhesion to the substrate.
b. Draw and label the main components of a focal adhesion to illustrate the extracellular matrix substrate, the binding proteins, at least 3 adaptor proteins, and the cytoskeletal proteins, connections to the nucleus. ( 5 points ).
2. Fibroblasts have been embedded in a 3D hydrogel substrate with binding sites as shown below. The hydrogel is tethered to posts at the top and bottom of the images but the long edges are not tethered. Over time, the hydrogel morphology changes as shown in the figure. a. Based on our discussions on how cells interact with their environments, sketch and describe what you expect the morphology and orientation of a random cell located in the center of the hydrogel to look like at each time point (i.e. Your answer should include 4 sketches of cells at Days 0, 7, 14, & 21 highlighting any changes in morphology that occur over time). Explain the reasoning behind your response. ( 8 points ).
b. Copy your sketch for the cell alignment at Day 21 only. In this sketch, represent the alignment of the stress fibers in the cell. On 2 or 3 of these stress fibers, add arrows indicating what direction the stress (tension) in the fiber is acting. ( 2 points ) c. Sketch for Days 0 and 21 how would your might change if there were no binding sites in the gel to which the cells could attach ( 2 points )?
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