Punjab State Board PSEB 12th Class Biology Important Questions Chapter 11 Biotechnology: Principles and Processes Important Questions and Answers.
PSEB 12th Class Biology Important Questions Chapter 11 Biotechnology: Principles and Processes
Very short answer type questions
Write the two components of the first artificial recombinant DNA molecule constructed by Cohen and Boyer.
- Antibiotic resistance gene and
- Plasmid vector of Salmonella typhimurium.
Suggest a technique to a researcher who needs to separate fragments of DNA.
Mention the uses of cloning vector in biotechnology.
Cloning vectors are used for transferring fragments of foreign DNA into a suitable host. They are also used to select recombinants from non-recombinants.
Why is it not possible for an alien DNA to become part of a chromosome anywhere along its length and replicate normally?
Alien DNA must be linked to ori or origin of replication site to start replication.
Why is it essential to have a ‘selectable marker’ in a cloning vector?
Selectable markers are essential to identify and eliminate non-transformants, by selectively permitting the growth of the transformant.
Biotechnologists refer to Agrobacterium tumifaciens as a natural genetic engineer of plants. Give reasons to support the statement.
This is because A. tumifaciens can transfer genes naturally by delivering a piece of T-DNA to plant cells. It has a tumour inducing plasmid.
Name the host cells in which micro-injection technique is used to introduce an alien DNA.
How does an alien DNA gain entry into a plant cell by ‘biolistics’ method?
In biolistics method cells are bombarded with high velocity micro-particles of gold or tungsten coated with DNA.
What is the host called that produces a foreign gene product? What is this product called?
The host that produces a foreign gene product is called competent host. The product is called recombinant protein.
Give any two microbes that are useful in biotechnology. [NCERT Exemplar]
E. coli and Saccharomyces cerevisiae.
What is EcoRI? How does EcoRI differ from an exonuclease?
EcoRI is restriction endonuclease enzyme. Exonuclease removes nucleotides from the ends of DNA while EcoRI makes cut at specific position within the DNA.
What is the significance of adding proteases at the time of isolation of genetic material (DNA)? [NCERT Exemplar]
Role of proteases is to degrade the proteins present inside a cell (from which DNA is being isolated). If the proteins are not removed from DNA preparation then they could interfere with any downstream treatment of DNA.
While doing a PCR, ‘denaturation’ step is missed. What will be its effect on the process? [NCERT Exemplar]
If denaturation of double-stranded DNA does not take place, then primers will not be able to anneal to the template, no extension will take place, hence no amplification will occur.
What would happen when you grow a recombinant in a bioreactor but forget to add antibiotic to the medium in which the recombinant is growing? [NCERT Exemplar]
In the absence of antibiotic, there will be no pressure on recombinants to retain the plasmid (containing the gene of your interest). Since, maintaining a high copy number of plasmids is a metabolic burden to the microbial cells, it will thus tend to lose the plasmid.
Short answer type questions
What is meant by gene cloning? [NCERT Exemplar]
Gene cloning refers to a process in which a gene of interest is ligated to a vector. The recombinant DNA thus produced is introduced in a host cell by transformation. Each cell gets one DNA molecule and when the transformed cell grows to a bacterial colony, each cell in the colony has a copy of the gene.
List the key tools used in recombinant DNA technology.
The key tools used in recombinant DNA technology are as follows:
- Restriction enzymes
- Polymerase enzyme
- Ligase enzyme ‘
- Host organism/cell.
(a) What are “molecular scissors”? Give one example.
(b) Explain their role in recombinant DNA technology.
Or Why are molecular scissors so called? Write their use in biotechnology.
(a) The restriction endonucleases are called molecular scissors, as they cut the DNA segments at particular locations, e.g., EcoRI. They are so called because they cut DNA at specific points.
(b) The restriction enzymes cut the DNA strands a little away from the centre of the palindromic sites, but between the same two bases on the opposite strands. This leaves single stranded portions with overhanging stretches called sticky ends on each strand as they form hydrogen bonds with their complementary cut counterparts. This stickiness at the ends facilitates the action of the enzyme DNA ligase.
Name the natural source of agarose. Mention one role of agarose in biotechnology.
The natural source of agarose is sea weed. Agarose is a natural polymer. It is used to develop the matrix for gel electrophoresis. It helps in the separation of DNA fragments based on their size.
For producing a recombinant protein (for therapeutic purpose) in large scale, which vector would you choose – a low copy number or high-copy number? [NCERT Exemplar]
High-copy number, because higher the copy number of vector plasmid, higher the copy number of gene and consequently, protein coded by the gene is produced in high amount.
What modification is done in the Ti plasmid of Agrobacterium tumefaciens to convert it into a cloning vector? [NCERT Exemplar]
T-DNA is the only essential part required to make Ti plasmid a cloning vector. The plasmid is disarmed by deleting the tumour inducing genes in the plasmid so that it becomes an effective cloning vector and remove it harmful effect.
Describe the role of CaCl2 in preparation of competent cells.
CaCl2 is known to increase the efficiency of DNA uptake to produce transformed bacterial cells. The divalent Ca+2 ions create transient pores in the bacterial cell wall, by which the entry of foreign DNA is facilitated into the bacterial cells.
(a) Why must a cell be made ‘competent’ in biotechnology experiments? How does calcium ion help in doing so?
(b) State the role of ‘biolistic gun’ in biotechnology experiments?
(a) A recombinant DNA transfer into the host cell, needs that the recipient cell must be made competent in order to receive and absorb the DNA, present in the surrounding. The calcium ions in the medium increase the efficiency with which DNA enters the bacterium through the pores in the cell wall.
(b) Biolistic or Gene Gun : It is a vectorless method in which DNA is directly introduced in the nucleus of plant cell. Plant cells are bombarded with high velocity micro particles of gold or tungsten coated with DNA.
Long answer type questions
(a) Name the selectable markers in the cloning vector pBR322? Mention the role they play. ‘
(b) Why is the coding sequence of an enzyme β-galactosidase a preferred selectable marker in comparison to the ones nam£d above?
(a) In pBR322, ampR and TetR, the two antibiotic resistant genes act as selectable markers. If an alien DNA ligates at the Bam HI site of tetracycline resistant gene in the vector pBR322, the recombinant loses the tetracycline resistance. Non-recombinant will grow on both the media containing tetracycline/ampicillin whereas recombinant will grow on ampicillin medium but not on medium containing tetracycline. In this case, one antibiotic resistance gene helps in selecting the transformants and the other antibiotic gene gets inactivated due to insertion of alien DNA.
Thus, selectable markers (ampR) help in indentifying and eliminating non-transformants and help in selecting those host cells which contain the recombinant vector i.e., transformants.
(b) The selection of recombinant by the inactivation of one of the antibiotic resistance gene is a cumbersome, complicated, time consuming technique involving plating both the recombinant and non-recombinant on the ampicillin medium and then on tetracycline containing medium. In insertional inactivation, the DNA inserted in the coding sequence of an enzyme p-galactosidase results in inactivation of the enzyme and the bacterial colony, with insert shows no colouration while those without inserted plasmid, form blue colour colonies. This is a simple, less cumbersome technique.