centrifugation

Question 1

what is centrifugation

Answer 1

a method to separate particles by applying centrifugal force. this depends on size, density and shape

Question 2

what can centrifugation determine

Answer 2

molecular weight
density
shape
changes to any of the above

Question 3

what is an interfering substance

Answer 3

a substance that is difficult to remove - this is possible with different sedimentation rates

Question 4

what changes the sedimentation rate

Answer 4

centrifugal force
density difference to liquid
size and shape
viscosity

Question 5

how do you calculate the relative centrifugal force

Answer 5

RCF = 1.118r (n/1000)^2

r = radius (mm)
n = rpm

OR

use a nomogram

RCF is not uniform in a centrifuge tube - it is the highest near the rotor and lowest near the axis. the average is in the middle of the tube

Question 6

how do you calculate the rpm

Answer 6

n = 945.7 (RCF/r)^1/2

OR

use a nomogram

Question 7

what sediments first in a cell

Answer 7

whole cell
cell debris
nuclei

Question 8

what sediments last in a cell

Answer 8

lysosomes

ribosomes

Question 9

what are the applications of centrifugation

Answer 9

removal of precipitates
sedimentation of isolated cells
isolation of organelles - choosing force based on sedimentation rate - makes a pellet

Question 10

what is a rate zonal density gradient

Answer 10

sample centrifuged and then the large particles move faster tan small ones - creates zones (bands)

Question 11

what is an isopycnic density gradient

Answer 11

sample separates on the basis of buoyant densities
sucrose forms density gradient
bands within a density gradient can be sampled with a pipette or punctured tube