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resit question-please help....

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resit question-please help....

Postby *susie* » Tue Aug 09, 2005 8:56 pm

i have an exam paper to do and i am stuck on the following question:

two sets of plants of the same spechies were grown under identical conditions except for ambient temperature. describe and explain the differences you would expect to see, in the lipid composition of the membranes, between the plants grown at 10degrees and those grown at 25degrees. (9 marks)

could anyone help me with the answer....PLEASE :) im really stuck as i know what temperature does to lipid membranes, just dont know how the composition of lipids is affected in growth at the different temperatures.

thank-you :D
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plant and cold stress

Postby fabienne » Wed Aug 10, 2005 10:16 am

if you compare plant at ambiant temperature to plant at 10 degrees, plant at 10 degrees are going to be smaller because of stress caused by cold whitch involve regulation of growing, regulation of genetic program to be able to survive to cold temperature. exemples of this regulation are to permit synthesis of proteins and sugar who are cryoprotectant (chaperonin, ....), to change the membrane fluidity

membranes are sensitive to low temperature, because low temperatures reduce membrane fluidity. this reduction of the fluidity willl reduce
-plasticity of membrane ( involved in trafficing between cells, shape and size changes during growth, ability to include new proteins in the membrane...)
-capacity not to "break" because of ice in the cell

Fluidity is determined by lipid composition and temperature

longer fatty acids in the lipids=higher melting temp
addition of double bonds in fatty acids=lower melting temp

plants can be classified as "chilling tolerant" or "chilling sensitive" (chilling is not freezing); chilling tolerant plants have a higher % of unsaturated fatty acids in membranes to maintain fluidity

this reorganisation of membrane is the result of changes in genetics programs what allow synthesis of enzymes or modification of the activity of proteins, involved in the composition of the membrane


good luck!
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Postby mothorc » Sat Aug 13, 2005 12:33 pm

I don't agree with fabien's explain because the concentration of lipit can be change but the structure is always const.(FAME's principle)
I think the question is more intersting if degree temperature mean degree in rotation. :wink:
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Postby har0bed1813 » Sun Aug 21, 2005 3:48 pm

you people are smart :idea: :wink:
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Postby mith » Sun Aug 21, 2005 6:01 pm

I think he did mean the different concentrations of lipids
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