Fluidity

Definition

Refers to the ability of molecules within a substance to move freely. In relation to cell membranes, it describes how easily lipids can move laterally within the phospholipid bilayer.

Related terms

Temperature:

Higher temperatures increase membrane fluidity because it adds energy for lipid molecules to move more quickly. Lower temperatures decrease fluidity as molecules slow down.

Unsaturated Fatty Acids:

Lipid molecules containing at least one double bond in their carbon chain. Unsaturated fatty acids increase membrane fluidity because the kinks in their structure prevent tight packing.

Phospholipid Flip-Flop: A rare event where a phospholipid molecule switches from one leaflet of the bilayer to the other. This process is slow and requires energy.