Bihar Board - Class 12 Biology - Chapter 11: Biotechnology: Principles and Processes Long Answer Question

Q.1. What is a polymerase chain reaction? What are the steps involved? Mention its applications.

A.1. The polymerase chain reaction is the process used in molecular biology to obtain several copies of a specific segment of DNA.

The following steps are involved in the process:

• Denaturation

• Annealing

• Extension

Applications:

PCR has its applications in the following fields:

• Forensic Science

• Research and genetics

• Medicine

Q.2. What are the properties of a good vector?

A.2. A good vector must possess the following properties:

1. The vector must be small in size so that it is easy to isolate and purify.

2. It should have an origin of replication, a base pair sequence where replication starts.

3. It should have a selectable marker that helps in selecting the transformed host cells.

4. The vector should have at least one unique recognition site to bind the foreign DNA.

Q.3. Mention any three vector-less methods that are used to introduce recombinant DNA into a competent host cell.

A.3. The three vector-less methods include:

1. Transformation: This is the process by which bacteria takes up the genetic material directly from the surroundings. For this, the bacterial cells are treated with calcium chloride. The cells are then incubated in ice and then subjected to very high temperature. This creates pores in the bacterial cell wall and the foreign DNA is taken up by the bacterial cell.

2. Microinjection: In this, the recombinant DNA is directly injected into the nucleus of the animal cell with the help of a microneedle.

3. Biolistics/Gene gun Method: The cells are bombarded with very high-velocity microparticles of gold and tungsten coated DNA.

Q.4. What is a Bioreactor? 

Ans: The bioreactors are the devices in the form of the vessel which contains various organisms or chemical substances that undergo the chemical processes and result in the formation of the biologically active substances. They consist of large vessels where the raw materials using microbial, plant, animal, or human cells are converted biologically into specific proteins. The advantages of Bioreactor over shake flask are:

a) To produce the optimum growth of the desired product, it provides the optimal conditions e.g., temp, pH, etc.

b) For testing the sample, a small volume of cultures can be withdrawn periodically from the bioreactor.

c) It has an agitation system, temp control system, from control system & pH control system.

Q.5. Mention the important properties which a good vector must possess?

Ans: The important properties which a good vector must possess are -

i) Size - The size of the vector must be small so that it helps them in purification and isolation easily.

ii) Origin of Replication – A site where replication starts and is made up of the sequence of base pairs. When the DNA is attached to this sequence then it will result in the replication within its host cell & thus, controls the number of copies of linked DNA.

iii) Selectable Marker - The host cells that contain the vector can be selected with the help of a gene called a selectable marker that results in the elimination of the non–transformant. It is used in genetic engineering.

iv) Cloning Sites - The site in the vector where the foreign/alien DNA attaches is also called the unique recognition site. A particular restriction enzyme will cut the vector-only at a particular recognition site.

Q.6. Describe any three vector less method of introducing the rDNA into a competent host cell?

Ans: The three vectors less method of introducing the rDNA into a competent host cell are:

i) Transformation: The bacterial cell is first treated with the specific concentration of divalent cation e.g., Ca2+ so that they can be competent enough to take up the DNA in the plasmid. The calcium ions increase the efficiency of DNA to enter into a bacterium through pores in its cell wall. By the process of incubating the cells with recombinant DNA on ice, then placing them at 420 C, and then again putting them back into ice the recombinant DNA can then be forced into cells. This helps the bacteria in taking up the recombinant DNA.

ii) Microinjection: With the help of a microneedle of the tip with a diameter (~ 4mm), the recombinant DNA can be injected directly into the nucleus of an animal cell.

iii) Biolistic / Gene gun: The cells of the DNA that are coated with particles of gold or tungsten are bombarded with high-velocity micro-gun.

Q.7. Why is Agrobacterium-mediated genetic transformation described as Natural Genetic engineering in plants?

Ans: The Agrobacterium tumefaciens-interceded plant genetic transformation measure requires the presence of two genetic segments situated on the bacterial Ti-plasmid. Basically, the main basic part is the T-DNA, which is characterized by conserved 25-base pair imperfect repeats at the closures of the T-region known as a border sequence. The tumor-inducing (Ti) plasmid is used as a cloning vector to transfer the desired gene into plants as they insert a part of their DNA in plants during the infection. The second is the virulence (vir) region, which is made out of in any event seven significant loci (virA, virB, virC, virD, virE, virF, and virG) encoding parts of the bacterial protein machinery which is mediating the T-DNA processing and transfer. The gene of interest is attached to the T-DNA so that it automatically gets transformed into plant cells thus, Agrobacterium tumefacien is known as the “Natural Genetic Engineer” of plants.

Q.8. Expand PCR? Describe the different steps involved in this technique?

Ans: The Polymerase Chain Reaction is the method of making millions of DNA copies from a DNA sample. It has two main reagents: primers (short single-stranded DNA fragments that are a complementary sequence to the target DNA), and DNA polymerase. The DNA polymerase is heat stable, that is Taq polymerase which is extracted from the bacteria Thermus aquaticus. Each cycle has three steps:

a) DENATURATION: In the first step, the two strands of the DNA helix are physically separated at a heat during a process called macromolecule denaturation.

b) RENATURATION / ANNEALING: In the second step, the temperature is lowered so that the primers can bind to the complementary sequences of DNA.

c) EXTENSION: The third step is the target DNA sequence will synthesize its copies by the process of the extension of the primers.  The temperature is raised to 750c. At this temperature, Taq – polymerase initiates DNA Synthesis at the 3-OH end of the primer.