Biology 1 Exam 2, Cell Biology October 2014

Name ___________________

Instructions Answer all of the following questions. Each response is worth up to 3 points unless otherwise noted. You have until 5pm on October 29th to submit your responses to LesleyBioHomework@gmail.com; if you would like to submit handwritten response, please make arrangements to do so during class on October 22th.

You may use notes, textbooks, the Internet and documentaries.

All responses must be in your own words.

You may consult with fellow classmates, but each student must turn in their own responses written in their own words; if any responses are found to be identical or very similarly worded, all students submitting those responses will receive no credit for the entire exam and may be reported to the Lesley University Academic Integrity Committee.

Plagiarism of any form will also be reported 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”: http://www.npr.org/blogs/health/2013/10/09/229167219/proposed-treatment-to-fix-genetic-diseases-raising-ethics-issues

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?

d. 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), what kind of protein is it? In other words, with the terms covered in chapter 5 of Biology, which one best applies to 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? What might happen if some mitochondria have less internal membrane?

f. What kind of microscope do you think was used to take this image? Why do you think so?

3. Below are two images of African green monkey cells at 4500x magnification, taken from a journal article by Manfred Schliwa who examined 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.

Interested in the effects of cytochalasin D on cell structure and function, Zofini decides to carry out similar experiments. Because the images obtained by Schliwa 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.

e. Why does the actin appear to be glowing red in the images?

F I GURE 2

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Who l e - moun t pr epa r a t i ons o f Tr i t on X- 100 - ex t r ac t ed ce l l s v i ewed i n a h i gh - vo l t age e l ec t ron m i c roscope . ( a ) Con t ro lce l l . No t e pr esence o f f i l amen t bund l es ( s t r ess f i be r s ) and mor e or l ess un i f orm f i l amen t ne t wor k ex t end i ng t hroughou t t he ce l l .(b ) Ce l l t r ea t ed w i t h 2 pg / m l cy t ocha l as i n D f or 15 m i n . Nume rous dense f oc i ( a r rowheads ) have f ormed t hroughou t t he cy t op l asm .The f i l amen t ous ne t wor k i s d i scon t i nuous; l a rge a r eas appea r t o be devo i d o f f i l amen t ne t wor k . S t r ess f i be r s a r e absen t . x 4 , 500.

cy t oske l e t ons t o cy t ocha l as i n D does no t i nc r ease t he degr ee o fne t wor k d i s rup t i on , depo l yme r i za t i on seems un l i ke l y . The r e -f or e , t he second poss i b i l i t y has been exp l or ed . I f d i sconnec t i onand / or br eak i ng o f f i l amen t s w i t h subsequen t r e l ease i n t o t hebu f f e r occur s , i t shou l d be poss i b l e t o r ecove r r e l eased com-ponen t s i n t he supe rna t an t . Nega t i ve s t a i n i ng o f t he supe rna t eo f cy t ocha l as i n - t r ea t ed cy t oske l e t ons r evea l s nume rous f i l a -men t f r agmen t s , 0 . 2 - 4 pa r t i n l eng t h wh i ch , by v i r t ue o f t he i rdecor a t i on w i t h S1 , can be shown t o be F - ac t i n ( F i g . 7) .F i l amen t f r agmen t s may a l so be encoun t e r ed i n supe rna t es o fDMSO - t r ea t ed con t ro l ce l l s , bu t a t a s i x t o t en t i mes l owe rf r equency (da t a based on t hr ee i ndependen t expe r i men t s ) .I n t e r es t i ng l y , supe rna t es o f cy t ocha l as i n - t r ea t ed cy t oske l e t onsf r equen t l y show wha t appea r t o be ne t wor k f r agmen t s , i . e . ,shor t ac t i n f i l amen t s i n end - t o - s i de con t ac t w i t h ano t he r ac t i nf i l amen t ( F i g . 7) . I f decor a t ed w i t h S1 , a r rowheads po i n tt owa rds t he s i t e o f con t ac t .

I nc r eased r e l ease o f ac t i n i n t o t he supe rna t e upon cy t ocha l -as i n D t r ea t men t o f cy t oske l e t ons was con f i rmed by SDSPAGE ( F i g . 8) . Dens i t ome t r y r evea l s an approx i ma t e l y sev -en f o l d i nc r ease i n t he amoun t o f a pro t e i n com i gr a t i ng w i t hr abb i t ske l e t a l musc l e ac t i n . O t he r po l ypep t i des enr i ched i nsupe rna t es o f cy t ocha l as i n D - t r ea t ed pr epa r a t i ons a r e bands o f100 , 000 mo l w t and a po l ypep t i de o f approx i ma t e l y 200 , 000mo l w t t ha t does no t com i gr a t e w i t h r abb i t ske l e t a l musc l emyos i n . Seve r a l o t he r bands a l so show a s l i gh t i nc r ease i ni n t ens i t y . I n gene r a l , t he r e i s an approx i ma t e l y t wo and a ha l f

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THE JOURNAL OF CELL B I OLOGY " VOLUME 92 , 1982

f o l d i nc r ease i n t o t a l pro t e i ns r e l eased upon cy t ocha l as i n t r ea t -men t vs . DMSO t r ea t men t , i f t he pro t e i n concen t r a t i on i nsupe rna t e de r i ved f rom an equa l numbe r o f ce l l s i s de t e rm i ned .

Me t abo l i c I nh i b i t or sBr i e f pr e t r ea t men t o f ce l l s w i t h i nh i b i t or s o f ene rgy me t ab -

o l i sm be f or e cy t ocha l as i n t r ea t men t abo l i shes t he ma r kedchanges i n ce l l shape , d i sso l u t i on o f f i l amen t cab l es , and f or -ma t i on o f dense f i l amen t ous aggr ega t es (3 , 15 , 26) . To t es twhe t he r such a t r ea t men t a l so i nh i b i t s , or o t he rw i se i n f l uences ,cy t ocha l as i n - i nduced d i s rup t i on o f t he t hr ee - d i mens i ona l cy -t oske l e t a l f i l amen t ne t wor k , BSC- l ce l l s we r e pr e t r ea t ed w i t ho l i gomyc i n , d i n i t ropheno l , 2 - deoxyg l ucose , or comb i na t i ons o ft hese i nh i b i t or s o f ene rgy me t abo l i sm . I n t hese expe r i men t s ,gross morpho l og i ca l changes norma l l y occur r i ng i n cy t ocha l -as i n - t r ea t ed , un i nh i b i t ed ce l l s a r e b l ocked. Cy t oske l e t a l pr ep -a r a t i ons , howeve r , r evea l ma r ked changes i n f i l amen t ne t wor ka r r angemen t ( F i g . 9) r esemb l i ng t hose obse r ved i n cy t ocha l -as i n - t r ea t ed cy t oske l e t ons ( see F i g. 7) . The f i l amen t ne t wor k i sd i s rup t ed i n many p l aces occas i ona l l y i n such a way t ha t" ho l es " o f up t o 1 - t Lm d i ame t e r appea r i n t he ne t wor k . Nu -me rous f r ee f i l amen t ends a r e obse r ved . Occas i ona l l y , zones o fi nc r eased f i l amen t dens i t y , wh i ch may be i n t e rpr e t ed as ea r l ys t ages o f f i l amen t f oc i f orma t i on , a r e encoun t e r ed i n t he ce l lpe r i phe r y . S t r ess f i be r s s t i l l appea r i n t ac t . D i s rup t i on o f t hef i l amen t ne t wor k w i t hou t s t r ess f i be r d i sso l u t i on or pronounced

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Published January 1, 1982

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. If Zofini is looking at these cells with 40x objective lens and a 10x objective lens, what is the total magnification with which the cells are being viewed? Show or explain how you obtained that magnification factor.

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4. Meat that has been salt cured, like jerky or salt cod, can last much longer than uncured meat. Salt curing is achieved by applying substantial amounts of salt to the surface of a piece of meat, which then dehydrates it, giving foods like jerky a dry texture compared to raw and cooked meats. Using concepts we have covered, explain why the application of salt has this effect. Hint: remember the gummy bear.

5. In The Andromeda Strain, the scientists look at a sample of Andromeda in an electron microscope.

a. Why are they using an electron microscope? Why not use a bright-field or fluorescent microscope?

b. Why are the scientists so stunned when Andromeda appears to be growing while being examined with an electron microscope?

6. Answer X or Y.

X. Plants need both chloroplasts and mitochondria to take care of their energy needs. If humans had chloroplasts and could photosynthesize, would we still need to eat food? Explain why in terms of concepts related to biological macromolecules and cell biology that we have covered.

Y. In the order in which they perform their functions in producing and distributing proteins, fill in the table below with the components of the endomembrane system.

Organelle Function1

2

3

4