Question

A technique used for the separation of the material according to their relative mass is known as centrifugation. Heavier substance will sink to the bottom while those with less mass will float. Name the cellular organelle concentrated at the top of the centrifuged mixture of a cell culture on the basis of density gradient centrifugation.
A. Nuclei.
B. Endoplasmic reticulum.
C. Mitochondria.
D. Ribosomes.
E. Membrane bound protein.

Answer 1

Hint: Centrifugation is the technique used to separate cell constituents, mixture of protein or genetic material. It is based on the behaviour of particles in an applied centrifugal field.

Complete Answer:
- The particles are separated on the basis of relative mass and density in centrifugation. Generally, the heavier particles are situated towards the outer side and lighter particles are shifted towards the inner side.
- A density gradient is either performed or formed during centrifugation. The denser particles with high relative mass settle at the bottom while the lighter ones with low relative mass float at the top.
- Sucrose, glycerol, cesium chloride can be used to form a density gradient with increasing density from top to bottom. The particles will separate and form bands in the area where their density matches with that of the gradient.
- In the options given above in the question, the density of the nucleus is the highest that is 2 and the density of mitochondria is the least that is 1.05-1.2.
- The density of ribosomes, endoplasmic reticulum, and membrane bound proteins is between 1.2-1.4.
- According to the density and relative mass nucleus will settle at the bottom and mitochondria will float at the top.

So, the correct option is C mitochondria.

Note: Centrifugation is based on the principle of sedimentation which states that the rate of sedimentation is dependent on the applied centrifugal field (G) directed radially outwards determined by the square of the angular velocity of the rotor in radians per second and the radial distance in cm of the particle from the axis of rotation.