Question

Protein lateral motion is much slower than that of lipids because proteins are larger than lipids. Also, some membrane proteins can diffuse freely through the membrane, whereas others are bound or anchored to other protein structures in the membrane.

The diffusion coefficient for the membrane protein fibronectin is approximately 7.00×10-13 cm2/sec, whereas that for rhodopsin is about 3.00×10-9 cm2/sec.

A) Calculate the distance traversed (in nm) by each of these proteins in 55.0 msec.

Distance traversed by rhodopsin =_____

nm

Distance traversed by fibronectin =_____

nm

B) Determine the expected and actual ratio of the diffusion coefficients, and determine whether the size difference accounts for the difference in the diffusion coefficients (D).

(The Mr of rhodopsin and fibronectin are 40000 and 460000 Da respectively.)

Expected D(rhodopsin:fibronectin) =

Actual D(rhodopsin:fibronectin) =

Does the size difference account for the difference in diffusion coefficients in these two proteins?