Centrifugation

Question 1

Define the formula for relative centrifugal field (RCF).

Answer 1

1.12e-5 x (RPM)^2 * r

Question 2

Name the five factors of sedimentation.

Answer 2

1. Mass
2. Density
3. Shape
4. Density of solvent
5. Friction

Question 3

In “18s rRNA”, what is “s”?

Answer 3

’s’ is the sedimentation coefficient.

s = 10^-13 seconds.

18s rRNA requires 18*10e-13 seconds to sediment.

Question 4

Examplify what cellular components would be segregated when centrifuging lysate at low-, medium- and high speed.

Answer 4

low speed: Cellular debris (membranes, large organelles).

High speed: Mitochondria, lysosomes, peroxisomes.

Ultra-high speed: Viruses, macromolecules.

Question 5

In the following formula, what is ‘k’?

t = k / s

Answer 5

t = time required for pelleting.
k = Clearing factor.
s = sedimentation constant.

The clearing factor differs from centrifuge to centrifuge.

Question 6

What’s the concept behind rate-zonal centrifugation?

Answer 6

You place your sample in a tube containing a solvent with a known density gradient. When centrifuging, your sample will segregate to the density strata that corresponds to its own density.

Question 7

How is rate-zonal centrifugation different from isopynic centrifugation?

Answer 7

In isopynic centrifugation, the density gradient of the solvent is produced during the centrifugation.

Question 8

What is a nemogram?

Answer 8

It’s an analog diagram with which you can figure out relative centrifugal force (RCF), radius of centrifuge and/or speed (RPM), by knowing two of the factors.