Membrane Flashcards
What is meant by the phase transition of a membrane?
Refers to the change in physical state of the membrane lipids depending on temperature
Above transition temperature, the lipids are in a fluid (liquid-crystalline) state
Below it, they are in a more ordered gel-like state
What physical state is the bacterial cytoplasm membrane normally in?
Liquid-crystalline
How does transition temperature compare between saturated fatty acids and unsaturated/branched fatty acids?
Transition temperature lower in unsaturated/branched fatty acids compared to saturated fatty acids
Why do bacteria have mechanisms to control and maintain the physical state of the membrane?
For membrane-bound proteins to perform properly, they need a certain amount of flexibility eg to undergo conformational change as part of their function. Only possible if the membrane is relatively fluid
How do bacteria control and maintain the physical state of the membrane?
In response to lowered temperature, the fatty acid composition of membrane phosphates can be altered to include more of those which have a lower transition temperature
This can be achieved by incorporation of different fatty acids as the phospholipids are being synthesised (E. coli) or conversion of pre-incorporated fatty acids (M. megaterium)
What kind of linkages are common in i) Eubacteria and ii) Archaea and other extremophiles?
i) Ester
ii) Ether
Specifically, how does E. coli respond to decreasing temperature?
They incorporate different fatty acids as the phospholipids are being synthesised
They increase the ration of oleate to stearate
Specifically, how does B. megaterium respond to decreasing temperature?
They convert pre-incorporated fatty acids
Desaturating enzyme is induced so there are more unsaturated fatty acids in membrane
How does the transition temperature of linoleic acid membrane compare to oleic acid membrane?
Linoleic acid membrane has a lower transition temperature than oleic acid
