Tropomyosin is a rod-shaped protein with a mass of 70 kDa and a sedimentation coefficient of 2.6S. Hemoglobin is a spherical protein with a slightly smaller mass of 65 kDa, but a much higher sedimentation coefficient of 4.31S. Which property of tropomyosin accounts for its slow sedimentation?
a. high particle density
b. elongated shape
c. high mass
d. low partial specific volume
e. overall net charge