Lecture 3- cell membranes

There are two populations of membrane proteins

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Unformatted text preview: ;the"fatty"acid"tail"[produced" by"desaturases"pg."96] !Organisms"put"unsaturated"phosolipids"into"the" membrane"and"the"presence"of"double"bonds" introduces"kinks"in"the"fatty"acid"backbone!"making"it" more"Mluid" !Organisms"can"control"the"Mluidity"of"their"membranes 10:25 !Membranes"remain"in"a"Mluid"state"over"a"relatively" wide"range"of"temps!"but"as"the"temp"drops,"the" molecular"motion"slows"down"and"Mluidity"is"lost"which" forms"a"semisolid"gel"(from"Mluid"state"to"solid"state) Saturated vs Non-saturated Fats (a)*Lipid*molcules*that*contain*saturated*hydrocarbon* tails*are*closely*packed (b)*Unsaturated*hydrocarbon*tails*have*kinks*that* prevent*lipid*molecules*from*packing*closely*together Fig. 5.6 10:25 Gardiner 2013 !Cholesterol&is&required&in&most&membranes Cholesterol Gardiner 2013 1202B 10:25 BIOLOGY • amount may vary with the type of membrane • Plasma - one cholesterol per phospholipid molecule • Other membranes (like those around bacteria) have no cholesterol 15 5 ! BIOLOGY 1202B Fig. 5.8 !When"inserted!"it"can"prevent"the"mebrane"from" • membrane must be fluid, about as fluid as salad oil to function • Cells can alter the lipid composition of membranes to compensate for changes in fluidity caused by changing temperatures. – cold-adapted organisms, such as winter wheat, increase the percentage of unsaturated phospholipids in the autumn. 10:25 Gardiner 2013 becomming"rigid !If"the"molecule"gets"too"hot"it"consevres"the"purpose"of" helping"to"hold"the"phospholipids"together !Some"organisms"live"in"hotsprings!"they"cant"have" their"membranes"Mlying"to"pieces"therefore"choles...
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