Exam 2, Part 2


You have 1 hour and 30 minutes to complete this part of the exam.
Write your responses to the questions on the answer sheet provided.
Each response is worth up to 3 points unless otherwise noted.
You may use your notes, any textbooks and the Internet.

All responses must be in your own words, with sources mentioned (no need to formally cite, but do give credit) when applicable. Plagiarism of any kind will be reported to the Lesley University Academic Integrity Committee.

1. Below is a painting by David Goodsell depicting a mycoplasma cell which has a diameter of 0.25µm (micrometers). The orange strands running throughout the interior is DNA. Ribosomes are shown in magenta, while phosopholipids are show in light green.

a. Based on the information presented here, is mycoplasma a prokaryote or eukaryote? Give two reasons why.

b. Mycoplasma can cause illness in humans. If a mycoplasma cell is found by a macrophage (a type of immune system cell), it will be taken into the macrophage to be digested and rendered harmless. What is this process is involved in this phenomenon and what steps are involved?

2. Read or listen to the NPR news story “Proposed Treatment To Fix Genetic Diseases Raises Ethical Issues” then answer the following questions.

a. Why do mitochondria have their own DNA?
b. Why can problems with mitochondrial DNA be lethal, as described in this news story in the case of Leigh’s Disease?
c. Why does the news story and the potential treatment it covers discuss the mother’s eggs so heavily?
atp synthase, life on earthd. The protein ATP synthase is essential for mitochondria to carry out their function in the cell, and in some instances of Leigh’s Disease, ATP synthase is not able to function properly. Given the location of ATP synthase (shown in this image from EO Wilson’s Life on Earth), of the kinds of proteins we’ve discussed in relation to cell biology, which one best categorizes ATP synthase? Which parts (turquoise, green, purple or orange) of ATP synthase are hydrophilic? (the grey objects are phospholipids)
e. Why do mitochondria have significant amounts of membrane within their interiors, as shown in the image below from the NPR news story? Is this a case of high or low surface-area-to-volume ratio? Why?
f. What kind of microscope do you think was used to take this image associated with the news story? Why do you think so?

3. Below are two images of African green monkey cells at 4500x magnification, taken from a journal article describing the effects of fungal toxin cytochalasin D on actin. The cell in panel b has been treated with cytochalasin D while the one in panel a was not. Note that the arrowheads in panel b point out clumps of actin not seen in a.
a. Which panel depicts the control experiment or condition? Explain.
b. What kind of microscope do you think was used to take this image? Why do you think so?
c. Are these cells prokaryotes or eukaryotes? How do you know?
d. Cytochalasin D disrupts the organization of actin within cells. What cellular structure will be affected, and what is one problem would you expect the cell treated with this toxin to have? Explain.

3, continued: Interested in the effects of cytochalasin D on cell structure and function, Zofini decides to carry out similar experiments. Because the images above have other cell structures in them and can thus be somewhat difficult to interpret, Zofini decides to use a fluorescent microscope to visualize actin networks. She obtains the images shown below. The cells on the left are normal while the cell on the right has been treated with cytochalasin D.
hela_100x       hela_100x_CD3 cropped
e. Why does the actin appear to be glowing red in the images?
f. How do fluorescent microscopy techniques allow Zofini to get a cleaner look at just actin (and the nucleus for reference) without the clutter of other cellular structures, like the mitochondria, ER, etc.?
g. Why do you think the cell on the right has a significantly different shape and appearance compared to the ones on the left?

4. Meat that has been salt cured, like jerky or salt cod, can last much longer than uncured meat because salt, according to Wikipedia, “inhibits the growth of microorganisms by drawing water out of microbial cells through osmosis.” Using concepts covered in the reading, explain why the application of salt has this effect.

5. Listen to or read this NPR news story on microbial transplants.
a. Why does Dr. Kelly describe the fecal transplant as being like an organ transplant?
b. Are the cells being transplanted eukaryotic or prokaryotic?
c. Why do researchers think this procedure is effective at combatting C. difficile?

6. The Andromeda Strain
a. When the scientists view the structure of Andromeda with an electron microscope, why is Dr. Leavitt (Ruth) so excited about the “wedge-shaped compartments” that Andromeda seems to exhibit? What insight might this provide into how Andromeda functions?
b. If Andromeda has a completely crystalline composition (no water, no membranes, etc.), what advantages or disadvantages would you expect it to have in space or on Earth when compared to terrestrial cellular life?
c. Can Andromeda be considered to be a black swan as we have discussed the concept? Why or why not?

7. Some scientists think that there could be alien life in methane oceans (essentially large bodies of liquid natural gas), such as those on Saturn’s moon Titan. Ignoring for the moment the conditions need to liquify methane (low temperatures and/or high pressures), could the kinds of cells we’ve been considering live in liquid methane? Explain your reasoning. Up to 6 points.


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