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Topic 2 - lipid bilayer (lec 3)

1312 moyes schulte 2008 pcpe fluidity pcpe fluidity

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Unformatted text preview: SLIDE 16 Fig. 5.7 Properties: membrane fluidity Homeoviscous adaptation Alterations in lipid composition to maintain membrane fluidity at different environmental temperatures Responses within an individual organism Evolutionary responses Fig. 13.12 Moyes & Schulte 2008 Fig. 2.3, Hill et al. 2004 membrane fluidity, but the process of Homeoviscous adaptation is adjusting the chemical composition of the membrane to compensate for the effect of the temp. so the membrane fluidity is maintained in the narrow desired range. It can happen at a level of an individual organism or across evolutionary time. > If we look at individual examples, in this diagram we have rainbow trout, they can live at temps around 5-20 degrees. A group of rainbow trouts that were living at 5 degree were transfered to 20 degrees. That increase in temp will make the membrane more fluid. To compensate in the trout there was an increase in the PC/PE ratio. Increasing (PC) which is the less fluid head group, while reducing (PE), which is the more fluid head group. the net effet of the increase of the ratio of PC/PE is to reduce fluidity, and that counters they effetc of the incerase in temp. The same thing happens in reverse when u move the trout from warm to cold, when u chill the fish the membrane becomes less fluid. To compensate for that the fish adjust the ratio of PC/PE this time they tend to reduce (PC) and increase (PE). The net effect of that is to increase fluidity and to counter the affect of the fallen temp. > You see similar patterns through evolutionary time. If for example u look at fish that are living and are adapted to environments of different temps, from tropical that live in 25 degrees, to antartic species that live in -2 to-3 degrees. If u look at either (PC) or (PE). You find the same pattren the degree of unsaturation, how many double bonds are present is higher in the species in the cold temps than it is in the species in the warm temp. There has been adaptation to the level of the membrane to these difference in temps to match the animal to the...
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