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cell engineering exam - (Jun/17/2009 )

actually these are not homework questions but some exam questions I might expect on friday. I tried to figure out the answers from the lecture but it doesn't really work and searching the net for this info is not that effective... If you can help me, I'd be really grateful.

1. how to recognize if the lamp is UV or white light without turning it on? -> is it that the UV lamp is made of clear glass and white light lamp is made of ground grass?
2. what do you do when you enter the lab and there is a blue lamp on? -> I have never encountered such information in any of the sources
3. what are the unstable components of medium? I know of L-glutamine but are there any else? antibiotics? hormones? growth factors?
4. after trypsinizing cell are coming off in stacks? how to solve this problem? (I heard about adding EDTA to weaken the cadherin-dependent junctions but I do not know if that's the reason and the answer)
5. you have discovered white precipitate in the medium - what does it mean?
6. what happens when the cells are starved more than 3 hours?
7. cells have been plated and on one plate the cells have become round - what does it mean? (neoplastic transformation?)
8. CHO cells have been plated in 3 densities, in one of the plates they have different shape, why?
9. how would you sterilize 50 ml of medium? (filter I guess) 50 microlitres of liquid?
10. what are the dyes that stain the living cells? (I mean not the fluorophores but the dyes) -> I heard only about neutral red


i will help with the first two:

1: the uv lamp is generally a deuterium lamp. if you look inside the glass you will see an electrode arrangement. on the outside you will see a window (usually extended from the main bulb on a side arm) where the light is directed by the electrode arrangement.

the visible lamp is generally tungsten and looks mostly like a normal bulb, with a simple element.

2: the blue light is probably uv irradiation to sterilize the area. shield your eyes and exit the lab.


UV bulbs/tubes in transilluminators and similar systems are just standard fluorescent tubes without a fluorescent coating on the inside.
4) Sounds OK to me. EDTA chelates metal ions that are important co-factors in many proteins.
5) Possibly contamination with bacteria, thought that would be a pretty heavy contamination. Other option is protein precipitation.
6) Cells will start to synchronize if serum starved.
7) Unhealthy cells - infection/contamination?
8) confluency changes cell shape, especially in fibroblasts.
9) filter is good for 50 ml, 50 ul is pretty hard, I wouldn't bother trying - use a bigger volume.
10) google vital stains.


just goes to show how set in our ways we are. i assumed aeiou was referring to spectrophotometer bulbs. i have a lot more experience with spectrophotometers than with transilluminators.

with transilluminators, i would expect a frosted (white coated) lamp to be visible and clear glass to be uv.

for 5) a white precipitate in medium is most likely a metal made into an insoluble salt (probably calcium phosphate).

for 9) 50 ul could be filter sterilized with a small spin filter if absolutely necessary.


10) i think the dye is Bromophenol blue...normally use during cell counting
9) yea...normally for animal culture media, we sterile filter by uisng 0.2 um size...if 50ul...mmmmmm think better go for bigger volume...hehehehe....
8) different shape coz the density population/ confuencecy will affect their shape formation

the rest i think i do agree with the rest


lol i just was updated that somebody has posted in the subject. thank u guys for ur help. i passed the exam year ago and i dont even remember now whether any of those questions were there. thanks again anyway. u might close it