Class 12 Biotechnology: Principles and Processes Mock Test (CBSE)

Topics in Biotechnology: Principles and Processes

• Principles of biotechnology
• Restriction enzymes
• Cloning vectors
• Competent host for transformation
• Processes of recombinant DNA technology
• Isolation of genetic material
• Amplification of gene using PCR
• Obtaining the foreign gene product
• Downstream processing

Biotechnology: Principles and Processes practice questions with answers

1. Q1Multiple choice·1 mark
   In the naming of restriction endonucleases, the Roman numeral that follows the name indicates:

   1. (a)the genus of the source organism
   2. (b)the species of the source organism
   3. (c)the order in which the enzyme was isolated from that strain of bacteria
   4. (d)the number of nucleotide bases recognized by the enzyme
   Show answer and step marks

   1. Correct option: (c)+1

   Answer: (c)
2. Q2Multiple choice·1 mark
   Which of the following enzymes is responsible for cutting DNA molecules at specific recognition sequences?

   1. (a)Exonuclease
   2. (b)DNA polymerase
   3. (c)Restriction endonuclease
   4. (d)DNA ligase
   Show answer and step marks

   1. Correct option: (c) Restriction endonuclease+1

   Answer: (c)
3. Q3Multiple choice·1 mark
   Which of the following is commonly used as a cloning vector to deliver foreign genes into plant cells?

   1. (a)pBR322
   2. (b)Disarmed Ti plasmid of Agrobacterium tumefaciens
   3. (c)Bacteriophage
   4. (d)pUC18
   Show answer and step marks

   1. Correct option: (b) Disarmed Ti plasmid of Agrobacterium tumefaciens+1

   Answer: (b)
4. Q4Short answer·2 marks
   State the significance of making a host cell 'competent' in recombinant DNA technology. Briefly explain how divalent calcium ions help in achieving this competency.
   Show answer and step marks

   1. Significance of competency: DNA is a hydrophilic molecule, so it cannot pass freely through cell membranes; therefore, bacterial cells must be made competent to take up recombinant DNA.+1
   2. Role of divalent calcium ions: they neutralise the negative charges on the DNA and on the cell surface and increase the efficiency with which DNA enters the bacterium through pores in its cell wall (uptake is completed by a brief heat shock).+1

   Answer: DNA is hydrophilic and cannot pass through cell membranes, so the host cell must be made competent to take up recombinant DNA. Divalent calcium ions neutralise the negative charges on the DNA and the cell surface and increase the efficiency with which DNA enters the bacterium through pores in its cell wall.
5. Q5Short answer·3 marks
   Explain the structure and functioning of a stirred-tank bioreactor used in recombinant DNA technology.
   Show answer and step marks

   1. Structure: a vessel, usually cylindrical with a curved base, which helps mix the reactor contents.+0.5
   2. Structure: an agitator (stirrer) fitted in the vessel.+0.5
   3. Structure: an oxygen delivery system (in a sparged stirred-tank reactor, a sparger bubbles sterile air through the medium).+0.5
   4. Structure, a further component, any one of: a temperature control system; a pH control system; a foam control system; sampling ports for withdrawing small volumes of the culture; or any other valid component.+0.5
   5. Functioning: the stirrer mixes the contents evenly and keeps oxygen available throughout the vessel.+0.5
   6. Functioning: optimum temperature, pH, substrate, salts, vitamins and oxygen are maintained, so cells grow in large volumes (100-1000 litres) and give large quantities of the recombinant product.+0.5

   Answer: A stirred-tank bioreactor is a usually cylindrical vessel with a curved base, fitted with an agitator (stirrer), an oxygen delivery system (sparger), temperature, pH and foam control systems and sampling ports. The stirrer mixes the contents evenly and keeps oxygen available throughout, and optimum conditions are maintained so cells grow in large volumes and yield large amounts of the recombinant product.
6. Q6Short answer·3 marks
   Describe the steps involved in the isolation of purified DNA from plant cells. State the specific role of chilled ethanol in this process.
   Show answer and step marks

   1. The plant cell wall is broken down with the enzyme cellulase, releasing DNA along with RNA, proteins, polysaccharides and lipids.+1
   2. RNA is removed by treatment with ribonuclease.+0.5
   3. Proteins are removed by treatment with protease (other molecules are removed by appropriate treatments).+0.5
   4. Role of chilled ethanol: added at the end, it precipitates the purified DNA out of solution, seen as a collection of fine threads in suspension that can be spooled out.+1

   Answer: The cell wall is broken with cellulase to release DNA with other macromolecules; RNA is removed with ribonuclease and proteins with protease (other molecules by suitable treatments); chilled ethanol is then added, which precipitates the purified DNA as fine threads in suspension.

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