1 · Saturated only · stiff (lab membranes)
The carbon chain of a saturated fatty acid () is straight — every C-C bond is single and rotatable, and the lowest-energy conformation is all-trans = a straight chain.Straight fatty-acid tails pack tightly against each other, like a bundle of aligned pencils:· Strong van der Waals forces
· Low fluidity
· Tend toward solid at room temperature (coconut oil, animal fat, dairy fat)
In cell and artificial-membrane experiments: such a tightly packed membrane restricts membrane proteins (receptors, ion channels, transporters) in their movement and conformational change → signalling slows.
An artificial membrane made only of saturated fatty acids is already near the gel-phase edge at 37 °C. Real cell membranes are never made of saturated fatty acids alone: they mix in unsaturated fatty acids and cholesterol, and the body actively regulates their fluidity, so saturated fat in the diet does not simply stiffen your cell membranes.