Q4 - Sedimentation Coefficient and Centrifugation Physics

Theoretical 1 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Centrifugation is one of the most important biochemical techniques in the separation and purification of biomolecules and organelles. The sedimentation speed (v) of specimens during centrifugal operation is proportional to the applied acceleration rate (gc), as shown in equation (1). S in the equation is called the sedimentation coefficient and is determined by the ratio between the centrifugal force applied to the object in the solvent (numerator) versus a parameter reflecting the magnitude of viscous resistance against sedimentation (denominator), as shown in equation (2). Vm : the molar volume of a sedimenting specimen rho : the densities of the specimen rho0 : the densities of the solvent r : the radius of the specimen when it is assumed to be spherical eta : the viscosity coefficient of the solvent NA : the Avogadro constant, 6.02x10^23. Indicate whether the following descriptions are true or false.

Using the information and data, determine which of the statements are true or which are false.

A. For organelles of the same size and shape, S can be used to estimate differences in organelle density.

B. Since many protein molecules have densities between 1.3 and 1.4 (g/mL), we can use S to distinguish sizes of spherical protein molecules.

C. Assuming that two ribosomal subunits of similar size are combined to form a large complex, S is approximately doubled.

D. Since it is commonly expected that the viscosity of a solvent will increase at low temperatures, S also decreases when chilled.

← Previous: Q3 Next: Q5 →

Question reproduced from IBO 2020, Theoretical Exam 1, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)