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Biotechnology: Principles and Processes - Competent Host and Transformation

Grade 12CBSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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DNA is a hydrophilic molecule; it cannot pass through cell membranes. To force bacteria to take up the plasmid, the bacterial cells must first be made 'competent' to receive DNA.

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Chemical Method: Cells are treated with a specific concentration of a divalent cation, such as Ca2+Ca^{2+}, which increases the efficiency with which DNA enters the bacterium through pores in its cell wall.

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Heat Shock Treatment: Recombinant DNA can be forced into cells by incubating the cells with recombinant DNA on ice, followed by placing them briefly at 42∘C42^\circ\text{C} (heat shock), and then putting them back on ice. This enables the bacteria to take up the recombinant DNA.

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Micro-injection: In this method, recombinant DNA is directly injected into the nucleus of an animal cell using a micro-needle.

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Biolistics or Gene Gun: Suitable for plants, cells are bombarded with high-velocity micro-particles of gold or tungsten coated with DNA.

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Disarmed Pathogen Vectors: 'Disarmed' pathogen vectors (like Agrobacterium tumefaciens or retroviruses), when allowed to infect the cell, transfer the recombinant DNA into the host without causing disease.

📐Formulae

Theat_shock=42∘CT_{heat\_shock} = 42^\circ\text{C}

Transformation Efficiency=Number of TransformantsAmount of DNA (μg)\text{Transformation Efficiency} = \frac{\text{Number of Transformants}}{\text{Amount of DNA (}\mu\text{g)}}

Competency Enhancement∝[Ca2+]\text{Competency Enhancement} \propto [Ca^{2+}]

💡Examples

Problem 1:

During the process of transformation, why is it necessary to place the cells on ice immediately after the 42∘C42^\circ\text{C} heat shock?

Solution:

Placing cells back on ice (0∘C0^\circ\text{C}) after the 42∘C42^\circ\text{C} heat shock helps in closing the transient pores created in the cell membrane.

Explanation:

The rapid change in temperature from 42∘C42^\circ\text{C} to 0∘C0^\circ\text{C} stabilizes the membrane and 'traps' the recombinant DNA inside the host cell, ensuring successful transformation.

Problem 2:

Identify the most suitable method for introducing foreign DNA into a plant cell without using a vector.

Solution:

Biolistics or Gene Gun method.

Explanation:

In this method, micro-particles of heavy metals like Gold (AuAu) or Tungsten (WW) are coated with the desired DNA and bombarded into the plant cells at high velocity to bypass the rigid cell wall.