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Centrifugation is a method used to separate solid particles from a liquid based on their size, shape, density, and viscosity. It is a technique that was discovered by a British engineer Benjamin Robins.
- Centrifugation is carried out in a centrifuge and works on the principle of centrifugal force.
- It has various applications in the fields of chemistry, biotechnology, genetic engineering, and the food industry.
- This separation technique is used in the dairy industry to separate fat (cream) from milk.
- It is also used in the purification of proteins as well as in the isolation of nucleic acids.
Multiple Choice Questions
Ques. Is the centrifugation technique used in wine industries?
- True.
- False
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Ans. (a) True
Explanation: Centrifugation is used in wine industries for separating the solids (grapes) from liquid. It is one of the methods of filtration to produce quality wine.
Ques. What is the average speed of an ultracentrifuge?
- 60,000 to 150,000 rpm.
- 6000 to 15000 rpm
- 40,000 to 45,000 rpm
- Above 15000 rpm
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Ans. (a) 60,000 to 150,000 rpm.
Explanation: Ultra-centrifuge is a type of centrifuge that rotates at a very high speed of about 60,000 to 150,000 rpm.
Ques. Separation of milk is carried out by which of the following methods?
- Gravity
- Centrifugal force
- Both a and b
- Only b
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Ans. (c) Both a and b
Explanation: Gravity and centrifugal force are the common methods used in the separation of fat from milk.
Ques. What type of centrifuge technique separates particles based on buoyant density?
- Differential centrifugation
- Density gradient centrifugation
- Analytical centrifugation
- Molecular centrifugation
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Ans. (b) Density gradient centrifugation
Explanation: Density gradient centrifugation separates particles based on their buoyant density or rate of sedimentation.
Ques. The separation of labeled DNA molecules is carried out by which method?
- CsCl gradient centrifugation
- Isopycnic centrifugation
- Rate-zonal centrifugation
- Sucrose gradient centrifugation
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Ans. (a) CsCl gradient centrifugation
Explanation: For the separation of DNA molecules a high density medium such as CsCl is used. Sucrose is a low-density medium. Isopycnic centrifugation separates particles based on their density, while rate zonal centrifugation separates particles based on their size.
Ques. What medium is used in density gradient centrifugation?
- Ficoll
- Dextran
- Percoll
- All of the above
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Ans. (d) All of the above
Explanation: In density gradient centrifugation dextran, ficoll, and percoll are used in the separation of whole cells.
Subjective Questions
Ques. How is a centrifuge operated?
Ans. The following are the steps needed to operate a centrifuge:
- Carefully add the samples in clean centrifuge tubes.
- Place the centrifuge tubes into the tube holders.
- Balance the samples when there are an even number of tubes.
- In case of odd numbers, balance with water-filled tubes.
- Now, close the lid of the centrifuge and set the required time and speed.
- Wait for the process to be complete and remove the tubes for the analysis.
Ques. Why is balancing necessary in centrifugation?
Ans. A centrifuge runs at a very high speed, therefore this speed magnifies any difference in the samples.
- If the centrifuge is not balanced, it can cause breakage of the rotor.
- Balancing can give accurate results without compromising efficiency.
Ques. What is the sedimentation rate in centrifugation?
Ans. A sedimentation rate is defined as the difference between the particles and the medium. The rate of sedimentation decreases with an increase in the velocity.
Ques. Differentiate between differential centrifugation and density gradient centrifugation.
Ans. The following is a table that shows the difference between the two:
| Differential Centrifugation | Density Gradient Centrifugation |
|---|---|
| The particles are separated based on their density, shape, size | In this method, the particles separated based on buoyant density and are concentrated in cesium chloride or sucrose |
| Separates cells, macromolecules, and organelles | Separates molecules or particles |
| A sugar solution is not required | A sugar solution is required |
Ques. What is the principle behind centrifugation?
Ans. Centrifugation works on the principle of sedimentation rate along with gravity force.
- A centrifugal force is created when the sample is rotated at a high speed. This force separates the solid particles from the liquid.
- The separation is based on the density of the particle, as the sample rotates the denser particles settle at the bottom.
- The light particles settle at the top and this type of separation is called sedimentation.
Ques. What are the characteristics of a centrifuge?
Ans. The following are the characteristics of a centrifuge:
- Speed- high-speed centrifuges are used for heavy samples and low-speed centrifuges for lighter samples.
- Volume- The volume of a centrifuge depends on the number of samples it can hold.
- Temperature- Centrifuges can control the temperature during the centrifugation process.
- Easy handling- The presence of control panels, and ease of sample loading and unloading makes it easy to handle.
Ques. What type of centrifuge is commonly used in clinical laboratories?
Ans. Benchtop centrifuge is commonly used in clinical laboratories.
- They are used to separate molecular components in a medium.
- Benchtop centrifuges are smaller in size, thus making them easier to handle.
Ques. What is the rate zonal centrifugation?
Ans. Rate zonal centrifugation is a process of separating biological components based on their shape and size.
- They are used to separate cells, proteins, nucleic acids, and other biomolecules.
- The rotor in a zonal centrifuge consists of a series of rings where the sample is placed and spun at different speeds.
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