CBSE Class 12 Biology Biotechnology Principles and Processes Worksheet Set A

Question. Which of the following would you choose as the safest and least cumbersome selectable marker-?
(a) Ampicillin resistance gene
(b) Tetracycline resistance gene
(c) Kanamycin resistance gene
(d) b Galactosidase gene

Answer: D

Question. Which one of the following steps is the first and the most important in the polymerase chain reaction?
(a) Annealing
(b) Primer extension
(c) Denaturation
(d) None of the above

Answer: B

Question. At what temperature does annealing of DNA and primer take place?
(a) 54°C
(b) 96°C
(c) 42°C
(d) 74°C

Answer: A

Question. The figure below is the diagrammatic representation of the E.Coli vector pBR 322. Which one of the given options correctly identifies its certain components (s)? 
(a) Ori-original restriction enzyme
(b) rop-reduced osmotic pressure
(c) Hind III, Eco RI -selectable markers
(d) ampR, tetR-antibiotic resistance genes

Answer: D

Question. Denaturation is the process of _________.
(a) Heating between 72°C
(b) Heating between 40 to 60°C
(c) Heating between 90 to 98°C
(d) None of the above

Answer: C

Question. Recombinant proteins are
(a) proteins synthesized in animals
(b) proteins synthesized by transgene in host cell by rDNA technology
(c) proteins synthesised in cells that are produced by protoplast fusion
(d) proteins synthesized in mutated cell lines

Answer: B

Question. Thermus aquatics is the source of _________.
(a) Vent polymerase
(b) Primase enzyme
(c) Taq polymerase
(d) Both a and c

Answer: C

Question. Insertional inactivation of the lac Z gene formsa.
(a) Blue recombinant colonies
(b) Colourless recombinant colonies
(c) Fluorescent green colonies
(d) There is no relation between the lac Z gene and colour of the colony.

Answer: B

Question. Polymerase used for PCR is extracted from _____________ .
(a) Homo sapiens
(b) Thermus aquaticus
(c) Escherichia coli
(d) Saccharomyces cerevisiae

Answer: B

Question. A host cell normally does not take up a foreign DNA until it has been made competent to do so. This is because:
(a) DNA is a hydrophilic molecule
(b) DNA is a very large molecule
(c) there are no receptors for DNA on the cell membrane
(d) DNA is an inert molecule

Answer: A

Assertion and Reason Based MCQs

Directions : In the following questions a statement of assertion (A) is followed by a statement of reason (R). Mark the correct choice as :
(A) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(B) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(C) Assertion (A) is true but reason (R) is false.
(D) Assertion (A) is false but reason (R) is true.

Question. Assertion (A) : EcoRI is restriction endonuclease enzyme.
Reason (R) : Exonuclease removes nucleotides from the ends of DNA.
Answer : B

 

Question. Assertion (A) : It is essential to have few cloning sites in cloning vector.
Reason(R) : It helps in identifying and eliminating non-transformants and selectively permitting the growth of the transformants.
Answer : B

Question. Assertion (A) : A primer is a small segment of DNA that binds to a complementary strand of DNA.
Reason(R) : Primers are necessary to stop the functioning of DNA polymerase enzyme and, therefore, are necessary in polymerase chain reaction.
Answer : C

Question. Assertion (A) : Restriction enzymes belongs to class nucleases.
Reason (R) : Nucleases are of two kinds : exo and endonucleases. Exonucleases remove nucleotides within the DNA.
Answer : C

Question. Assertion (A) : Thermus aquaticus, is used in PCR technique.
Reason (R) : It is a heat-stable DNA polymerase.
Answer : A

 

Question. Assertion (A) : E. coli having pBR322 with DNA insert at BamH I site cannot grow in medium containing tetracycline.
Reason(R) : Recognition site for BamH I is present in tetR region of pBR322.
Answer : A

Question. Assertion (A) : β-galactosidase coding sequence act as a selectable marker.
Reason (R) : Enzyme galactosidase converts the galactose into lactose.
Answer : A

Question. Assertion (A) : Agarose gel electrophoresis is used to check the progression of a restriction enzyme digestion.
Reason (R) : Restriction enzyme digestions are performed by incubating purified DNA molecules with restriction enzyme.
Answer : B

Question. Assertion (A) : Any fragment of DNA, when linked to the ori region, can be initiated to replicate.
Reason (R) : Ori is a genetic sequence that acts as the initiation site for replication of DNA.
Answer : A

Question. Assertion (A) : DNA is positively charged molecule.
Reason (R) : DNA moves towards the positive electrode (anode).
Answer : D

Very Short Answer Type Questions

Question. What does H in ‘d’ and III refer to the enzyme Hind III?
Answer : (i) The first letter ‘H’ indicates the genus of the organism from which the enzyme was isolated, H = genus Haemophilus. (ii) The fourth letter d indicates the particular strain used to produce the enzyme, d = strain Rd. (iii) The Roman numerals denoted the sequence in which the restriction endonuclease enzyme from that particular genus, species and strain of bacteria have been isolated-III, i.e., third restriction endonuclease to be isolated from this species.

Question. Restriction enzymes should not have more than one site of action in the cloning site of a vector. Comment.
Answer : If the restriction enzymes have more than one recognition site in a vector, then the vector itself will get fragmented on treatment with the restriction enzymes.

Question. Why is it not possible for an alien DNA to become part of chromosome anywhere along its length and replicate?
Answer: For multiplication of any alien DNA, it needs to be a part of a chromosome which has a specific sequence known as 'origin of replication‘.

Question. Why is it not possible for an alien DNA to become part of a chromosome anywhere along its length and replicate normally?
Answer: Alien DNA must be linked to ori or origin of replication site to start replication.

Question. Why is it essential to have selectable marker in a cloning vector? 
Answer: Selectable markers are essential to identify and eliminate non-transformants (no recombinant DNA), and selectively permitting the growth of the transformants (host cells bearing recombinant DNA).

Question. Name two main steps which are collectively referred to as down streaming process. Why is this process significant?
Answer: Separation and Purification.
This process is essential because before reaching into market, the product has to be subjected for clinical trial and quality control.

Question. Differentiate between plasmid DNA and chromosomal DNA? 
Answer: Plasmid DNA is extranuclear DNA, found in protoplasmic whereas chromosomal DNA is the nuclear or genetic DNA which is found within the nucleus.

Question. Do biomolecules (DNA and protein) exhibit biological activity in anhydrous conditions? 
Answer : Biomolecules (DNA, and protein) exhibit change in biological activity in anhydrous conditions, In non-aqueous or anhydrous conditions the rigidity of protein and DNA increases due to the weakening of hydrogen bond strength. It results into the change in overall free energy, which is the combined effects of the exposure of the interior polar and non-polar groups and their interaction with water. In absence of aqueous condition, the free energy change is negative, which is responsible for the denaturation of biomolecules. Increasing strength of hydrogen-bond causes water to primarily bond with itself and not to be available for the hydrating structure of proteins or DNA, or for dissolving ions. On the other hand, if the water-water hydrogen bond strength reduces then the exchange mechanisms operating within the cell, such as hydrogen bonded water chains within and between proteins and DNA, will become non-operational. It will further leads to the denaturation.

Question. What modification is done on the Ti-plasmid of Agrobacterium tumefaciens to convert it into a cloning vector? K Thinking Process T-DNA is the only essential part required to make Ti-plasmid a cloning vector.
Answer : The plasmid is disarmed by deleting the tumour inducing genes in the plasmid. So, that it become an effective cloning vector. The modified tumour inducing (Ti) plasmid of Agrobacterium tumefaciens will no longer remain pathogenic to the plants but still deliver genes of interest into a variety of plants.

Question. What does ‘competent’ refer to in competent cells used in transformation experiments?
Answer : DNA being a hydrophilic molecule can not pass through cell membranes. Therefore, the bacteria should be made competent to accept the DNA molecules. Competent means bacterial cells, on treatment with chemicals likeCaCl2, are made capable of taking up foreign DNA.

Short Answer Type Questions

Question. A recombinant DNA molecule was created by ligating a gene to a plasmid vector. By mistake, an exonuclease was added to the tube containing the recombinant DNA. How does this affect the next step in the experiment, i.e., bacterial transformation? K Thinking Process Bacterial transformation is the process by which bacterial cells take up naked DNA molecules (exogenous or foreign DNA).
Answer : The experiment will not likely to be affected as recombinant DNA molecule is circular and closed, with no free ends. Hence, it will not be a substrate for exonuclease enzyme which removes nucleotides from the free ends of DNA.

Question. Describe the role of CaCl2 in the preparation of competent cells?
Answer : CaCl2 is known to increase the efficiency of DNA uptake to produce transformed bacterial cells. The divalent Ca+2 ions create transient pores on the bacterial cell wall by which the entry of foreign DNA is facilitated into the bacterial cells.

Question. What would happen when one grows a recombinant bacterium in the bioreactor but forget to add antibiotic to the medium in which the recombinant is growing?
Answer : In the absence of antibiotic, there will be no pressure on recombinants to retain the plasmid (containing the gene of our interest). Since, maintaining a high copy number of plasmids is a metabolic burden to the microbial cells, it will thus tend to loose the plasmid.

Question. Restriction enzymes that are used in the construction of recombinant DNA are endonucleases which cut the DNA at ‘specific’-recognition sequence? What would be the disadvantage if they do not cut the DNA at specific-recognition sequence?
Answer : If the restriction enzymes would cut DNA at random sites instead of at specific sites, then the DNA fragments obtained will not have ‘sticky ends’. In the absence of sticky ends, construction of recombinant DNA molecule would not be possible.

Question. A plasmid DNA and a linear DNA (both are of the same size) have one site for a restriction endonuclease. When cut and separated on agarose gel electrophoresis, plasmid shows one DNA b and, while linear DNA shows two fragments. Explain.
Answer : When a plasmid DNA and a linear DNA having one site for a restriction endonuclease are cut and separated, plasmid shows one DNA band, while linear DNA shows two band because of difference in their basic structure. Plasmid is a circular DNA molecule and when cut with these enzyme, it becomes linear but does not get fragmented due to presence of only one restriction site, whereas a linear DNA molecule gets cut into two fragment.

Question. How are 'Sticky ends‘ formed on a DNA strand? Why are these so-called?
Answer: 1. Restriction enzymes cut the 2 strands of DNA a little away from the centre of palindrome site, but between the same two bases on opposite strands. As a result, single-stranded over hanging stretches of DNA called sticky ends are left at each end.
2. The Sticky ends are named so because they form hydrogen bonds with their complementary cut counterparts. The stickiness helps in the action of DNA ligase.

Question. Why is Agrobacterium mediated genetic transformation describe as natural genetic engineering in plants?
Answer: (i) Agrobacterium tumefaciens pathogen of dicot plants is able to deliver a piece of DNA known as T-DNA to transform normal plant cell into tumour.
(ii) Ti plasmid of Agrobacterium tumefaciens has been modified into a cloning vector, which is no more pathogenic to the plant but still able to use the mechanism to deliver genes
into a variety of plants.
iii. Since this process occur without human intervention, it is described as natural genetic engineering.

Question. How is a continuous culture system maintained in a bioreactor?
Answer: In a continuous culture system, the used medium is drained out from one side while the fresh medium is added from the other to maintain the cells in their physiologically most active log/exponential phase. The continuous culture method produces larger biomass leading to a higher yield of the desired protein.

Question. Explain any two methods of vector less gene transfer? 
Answer: (i)Microinjection-In this method rDNA is directly injected into the nucleus of an animal cell
(ii) Biolistics or gene gun-In this the target cells are bombarded with high velocity particles of gold or tungsten coated with DNA.

Question. DNA being hydrophilic cannot pass through cell membrane of a host cell.
Explain how does recombinant DNA get introduced into the host cell to transform the later?
Answer: (i)Chemical and heat shock method -the bacterial cells are treated with specific concentration of divalent cation such as calcium, rDNA is forced into such cells by incubating rDNA on ice, followed by placing them briefly at 420c and placing them back on ice.
.(i) Microinjection-In this method rDNA is directly injected into the nucleus of an animal cell
(ii) Biolistics or gene gun-In this the target cells are bombarded with high velocity particles of gold or tungsten coated with DNA.

Question. What is meant by gene cloning?
Answer : 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. This is gene cloning.

Diagram Based Questions:

1. A schematic representation of Polymerase Chain Reaction (PCR) up to the extension stage is given below. Answer the questions that follow: 

Question. Identify C and mention its importance in PCR.
Answer: C-DNA polymerase or Taq polymerase.
Importance in PCR: It extends the primers using the nucleotides provided in the reaction medium and the genomic DNA as the template. Taq polymerase is thermostable and withstands the high temperature used in denaturation process.

Question. Name the process - A.
Answer: A-Denaturation of the double stranded DNA.

Question. Identify B.
Answer: B-Primers

Question. A schematic representation of Polymerase Chain Reaction (PCR) up to the extension stage is given below. Identify A, B C & D:
Answer: 
A - Heat
B - Primers
C - Deoxynucleotides
D - 30

Case Based Questions:

CASESTUDY-I

Read the following and answer any four questions from (i) to (v) given below
'The vectors are DNA molecules that can carry a foreign DNA segment and replicate inside the host cell. Vectors may be plasmids, bacteriophages (viruses that attack bacteria), cosmids, yeast artificial chromosomes (YACs), Bacterial artificial chromosomes (BACs) and viruses. The most widely used, versatile, easily manipulated vector PBR 322 is an ideal plasmid vector. Features that are required to facilitate cloning into a vector includes origin of replication (Ori) which is a specific sequence of DNA bases responsible for initiating replication, selectable marker genes and cloning sites.

Question. A and B shown in the figure respectively indicates 
(a) Pvu II and Cla I
(b) ROP and Sal l
(c) amp^R and tet^R
(d) tetR and ampR.

Answer: C

Question. Selectable markers in vector
(a) are responsible for replication
(b) help in selecting transformants from non-transformants
(c) code for proteins involved in the replicating plasmids
(d) contain unique recognition sites.

Answer: B

Question. Plasmid vectors are
(a) dsDNA molecule
(c) present in bacteria and yeast
(b) extra-chromosomal
(d) all of these.

Answer: D

Question. p in pBR 322 denotes that it is a
(a) plasmid
(b) prokaryote
(c) protist
(d) plant cell.

Answer: A

Question. Ori is a specific DNA sequence that help in
(a) attachment of primers
(b) initiation of replication
(c) extension of DNA base
(d) initiation of denaturation.

Answer: B

CASE STUDY -II

2. Read the following and answer any four questions from (i) to 8(v) given below:
Rajat is a student of biotechnology. His professor tells him that for transformation with recombinant DNA the bacterial cells must be made capable of taking up DNA as DNA do not pass through membrane.
While doing experiment in the lab, Rajat noticed that bacterial cells were not taking up the foreign DNA even after treating it with sodium ion. He asked his professor, the reason behind this. His professor explained that he should check the valency and charge of the ion that he is using for the treatment.

Question. rDNA stands for
(a) reduced DNA
(b) red DNA
(c) recombinant DNA
(d) related DNA.

Answer: C

Question. Which of the following statements with regard to DNA is correct?
(a) DNA is a positively charged molecule having two polynucleotide chains.
(b) Nitrogen bases of two polynucleotide chain form complementary pairs. i.e., A opposite G and T opposite C.
(c) Backbone of DNA chain is built up of alternate deoxyribose sugar and phosphate group.
(d) Both (a) and (c)

Answer: C

Question. Assertion: Competent host is essential for transformation with rDNA.
Reason: Transfer of DNA in a prokaryotic cell is called transfection.
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.

Answer: C

Question. It is difficult for DNA to pass through the membrane as
(a) it is a hydrophilic molecule
(b) it is a hydrophobic molecule
(c) it is a circular molecule
(d) it changes its shape when it comes in contact with host cell

Answer: A

Question. What type of ions are used for DNA mediated gene transfers?
(a) Divalent anions
(b) Divalent cations
(c) Monovalent cations
(d) Monovalent anions

Answer: B

 

           Very Short Answer

Q1)       What is gene cloning?

Q2)       Define biotechnology?

Q3)       What is origin of replication?

Q4)       Who observed that enzymes have the capability of cutting DNA strands in a particular fashion?

Q5)       Where is the use of traditional hybridisation procedure?

             

              Short Answer

Q6)       Why the origin of replication is important?

Q7)       What are the two techniques enable the birth of modern biotechnology?

Q8)       What are the three basic steps in genetically modifying an organism?

Q9)       Define recombinant DNA?

Q10)     What do you mean by plasmid?

             

              Long Answer

Q11)     State the difference between exonuclease and endonuclease?

Q12)     Explain cloning vectors and what are its features that are required to facilitate cloning into a vector?

Q13)     State the difference between genomic DNA and plasmid DNA?

Q14)     Write short notes on restriction enzymes?

Q15)     Explain the steps that used in the processes of recombinant DNA technology?

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