Practice question

Regulation of fluidity reflects balance between order and disorder of fatty acyl chains governing membrane physical properties and protein function. Saturated acyl chains straight all trans conformation maximize van der Waals contacts small area per lipid about forty eight square angstroms low fluidity high transition temperature. Cis double bond introduces kink thirty degree bend reducing contact area to about sixty square angstroms increasing free volume lowering transition temperature fifty degrees increasing lateral diffusion coefficient and rotational freedom measured by fluorescence anisotropy diphenylhexatriene EPR order parameter. Polyunsaturated arachidonic docosahexaenoic more fluid. Longer chains raise Tm via more contacts decreasing fluidity. Temperature increase disorders chains raising fluidity; decreasing induces gel phase. Cholesterol biphasic modulates ordering. Cells homeoviscously adapt bacteria desaturase induction at low temperature, poikilotherms increased unsaturation winter. Therefore statement that membrane fluidity increases with unsaturated fatty acids accurately describes molecular basis of chain packing disruption enabling maintenance of functional liquid crystalline state required for permeability protein activity vesicular trafficking and signaling platform formation.