Unsaturated acyl chains are hydrocarbons chains that have one or more double bonds. Double bonds create "kinks" in the chains. Thus, fatty acids can not pack compactly with one another and therefore cause more movement in the membrane. A membrane that has lipids with unsaturated acyl chains at high temperature would be most fluid. While a membrane with lipids with saturated acyl chains at low temperature is least fluid.
To schedule a session with a great biochemistry tutor in NYC or online, click here.