3. Centrifugation is the technique of separating
components where the centrifugal force/
acceleration causes the denser molecules to move
towards the periphery while the less dense particles
move to the center.
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4. A particle whether it is a precipitate a macromolecule or a cell organelle is
subjected to a centrifugal force when it is rotated at a high rate of speed.
The centrifugal force F is denoted by equation :
F = mω2 r
Where
F = intensity of the centrifugal force
m = effective mass of the sedimenting particle
ω = angular velocity of rotation
r = distance of the migrating particles from the central axis of
rotation
Relative Centrifugal Force (RCF)
Relative centrifugal force is the measure of the strength of rotors of different types and
sizes.RCF is the perpendicular force acting on the sample that is always relative to the
gravity of the of the earth.
The formula to calculate the relative centrifugal force (RCF) can be written as:
RCF (g Force)= 1.118 × 10-5 × r × (RPM)2
where r is the radius of the rotor (in centimeters), and RPM is the speed of the rotor in
rotation per minute.
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5. A centrifuge is a device used to separate
components of a mixture on the basis of their
size, density, the viscosity of the medium, and
the rotor speed.
• The centrifuge is commonly used in laboratories
for the separation of biological molecules from a
crude extract.
• In a centrifuge, the sample is kept in a rotor
that is rotated about a fixed point (axis),
resulting in strong force perpendicular to the
axis.
• There are different types of centrifuge used for
the separation of different molecules, but they
all work on the principle of sedimentation.
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6. It consist of two components, an electric motor to spin the
sample and a rotor to hold tubes.
LOW SPEED CENTRIFUGE HIGH SPEED CENTRIFUGE
ULTRA CENTRIFUGE
LOW SPEED
CENTRIFUHE
HIGH SPEED
CENTRIFUHE
ULTRA CENTRIFUHE
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7. A centrifuge rotor is the rotating unit of the
centrifuge, which has fixed holes drilled at
an angle. Test tubes are placed inside these
holes and the rotor spins to aid in the
separation of the materials.
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10. Density gradient centrifugation is based on the principle that molecules settle
down under a centrifugal force until they reach a medium with the density the same
as theirs.
In this case, a medium with a density gradient is employed, which either has to
decrease density or increasing density.
There are two forms of Density gradient centrifugation :
Rate zonal centrifugation
Isopycnic or equilibrium density gradient
centrifugation
Rate zonal centrifugation
Isopycnic or equilibrium density gradient
centrifugation
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11. Differential centrifugation is based upon the differences in the sedimentation
rate of biological particles of different size and density.
As the increasing centrifugal force is applied, initial sedimentation of the
larger molecules takes place.
Further particles settle down depending upon the speed and time of
individual centrifugation steps and the density and relative size of the particles.
The largest class of particles forms a pellet on the bottom of the centrifuge
tube, leaving smaller-sized structures within the supernatant.
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12. To separate two miscible substances
To analyze the hydrodynamic properties of macromolecules
Purification of mammalian cells
Fractionation of sub-cellular organelles (including
membranes/membrane fractions) Fractionation of membrane vesicles
Separating chalk powder from water
Removing fat from milk to produce skimmed milk
Separating particles from an air-flow using cyclonic separation
The clarification and stabilization of wine
Separation of urine components and blood components in forensic
and research laboratories
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13. Carefully read the manual before using centrifuges .
Select proper operating conditions
Check rotor for cleanliness and for damage
Select proper rotor of definite size
Be sure the rotor is clean and undamaged
Keep accurate record of centrifuge and rotors
Carefully clean rotors after centrifugation.
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