Answer
Some molecules of the transmembrane proteins are anchored to specific parts of the cell cortex and are not able to freely rotate within the membrane plane.
Work Step by Step
Some molecules of the transmembrane proteins are anchored to specific parts of the cell cortex and are not able to freely rotate within the membrane plane. This causes an excess of transmembrane proteins over attachment sites in cortex and some transmembrane protein molecules are not anchored and rotate freely, this diffusing in the membrane. Measurement software of protein mobility show that there are two types of transmembrane proteins, some are anchored and some that are not.
