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Author: Subject: Effect of extreme conditions on the plasma membrane

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[*] posted on 13-2-2011 at 02:51
Effect of extreme conditions on the plasma membrane

I'm not asking to be spoon-fed or anything, I've done my homework/research but I'm still not sure on what ACTUALLY is happening. A friend of mine got it as a school prac, and I'm actually curious as to what is happening and I'm not exactly sure.

Blocks of beetroot (contain cells that have chromoplasts) are exposed to a number of different conditions:
- Heat (different temperatures)
- pH (pH 3, 7 and 9)
- Alcohol (0.1%, 1%, 5%, 10%, 50%)

The plasma membrane is damaged from all of these. The extremities (50% ethanol, 80 degrees celcius and pH 9) of course, having the most destructive effects, which is apparent due to the large concentration of purple chromoplasts in the solution of 25ml of water in each test tube.

This is where I want to have my conclusions verified:

- I'm not sure on the effect that acids/bases have on proteins and the phospholipid bilayer. Acids contain H+ ions which might bind themselves to the proteins imbedded within the membrane. This would make the proteins become denatured. I suppose the hydroxide could do similar and bind with a H+ ion and produce water creating damage/holes in the membrane. This is all speculation.

- Alcohol is lipid-soluble and over time will break down the phospholipid bilayer.

- The kinetic energy of heat will break the hydrogen bonds within proteins and denature them, to similar effects.

- More kinetic energy allows the membrane to have an increased fluidity, increasing permeability.

- I heard lysosomes have their enzymes activated at a pH of 4.8, but I'm doubtful if this had much impact on the experiment.

I would be very appreciative if I can have this cleared up and if I am correct, to expand on anything I have left out.

Thank you
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Biochemicus Energeticus

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[*] posted on 13-2-2011 at 07:54

Sounds mostly good to me.
Acid/base effects: Don't forget ion channels that actually cross the membrane, and what it would do to them. Denaturation is an important factor, but I'm pretty sure that at pH9 many proteins would be still ok and not denature, simiarly at pH3 some would surely be ok. Also, don't forget osmolarity. Net influx of i.e. H+ into the cells would screw them up big time, at first it would mess with intracellular signalling, then start killing vital enzymes through protonation. All metabolic processess woudl be altered, damaged, and cease.
For EtOH, I'd consiser osmolarity again (less so the ability to dissolve lipids), even at 10%EtOH, you effectively get swelling and permeabilisation of the membrane (leakage of cell metabolites).

Temp: I'd guess that it is more the effect on proteins (denaturation) than increase the fluidity of the membrane that proves fatal. I'd read up a bit on what denaturation is.
Good luck.

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