Describe the role of CaCl 2 in the preparation of competent cells.

In the recombinant DNA technology, the desired gene is inserted into the host cell with the help of vectors. The DNA is a hydrophilic molecule which cannot be easily introduced into other cells. Thus, the host cells are first made capable to take up these molecules so that this DNA may integrate itself in the host genome for the expression of genes and the products could be obtained. Such host cells are called competent hosts. The CaCl 2 is used to increase the competency of the bacterial cells. It contains divalent cations, calcium which creates pores in the bacterial cell wall. This enables the bacteria to take up foreign DNA through the pores.

E M B I B E

NCERT Exemplar Biology - Class 12>Chapter 11 - Biotechnology: Principles and Processes>SHORT ANSWER TYPE QUESTIONS>Q 1

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What is meant by gene cloning?

Important Questions on Biotechnology: Principles and Processes

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NCERT Exemplar Biology - Class 12>Chapter 11 - Biotechnology: Principles and Processes>SHORT ANSWER TYPE QUESTIONS>Q 2

Both a winemaker and a molecular biologist who had developed a recombinant vaccine claim to be biotechnologist. Who in your opinion is correct?

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NCERT Exemplar Biology - Class 12>Chapter 11 - Biotechnology: Principles and Processes>SHORT ANSWER TYPE QUESTIONS>Q 3

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?

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NCERT Exemplar Biology - Class 12>Chapter 11 - Biotechnology: Principles and Processes>SHORT ANSWER TYPE QUESTIONS>Q 4

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 these do not cut the DNA at specific-recognition sequence?

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NCERT Exemplar Biology - Class 12>Chapter 11 - Biotechnology: Principles and Processes>SHORT ANSWER TYPE QUESTIONS>Q 5

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 band while linear DNA shows two fragments. Explain.

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NCERT Exemplar Biology - Class 12>Chapter 11 - Biotechnology: Principles and Processes>SHORT ANSWER TYPE QUESTIONS>Q 6

How does one visualise DNA on an agarose gel?

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NCERT Exemplar Biology - Class 12>Chapter 11 - Biotechnology: Principles and Processes>SHORT ANSWER TYPE QUESTIONS>Q 7

A plasmid without a selectable marker was chosen as vector for cloning a gene. How does this affect the experiment?

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NCERT Exemplar Biology - Class 12>Chapter 11 - Biotechnology: Principles and Processes>SHORT ANSWER TYPE QUESTIONS>Q 8

A mixture of fragmented DNA was electrophoresed in an agarose gel. After staining the gel with ethidium bromide, no DNA bands were observed. What could be the reason?

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NCERT Exemplar Biology - Class 12>Chapter 11 - Biotechnology: Principles and Processes>SHORT ANSWER TYPE QUESTIONS>Q 9

Describe the role of CaCl₂ in the preparation of competent cells.