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Question
Assertion : Bacterial cells are made competent before transformation.
Reason : They are treated with a divalent cation in the process of making them competent.
Select the appropriate option.
Assertion : Bacterial cells are made competent before transformation.
Reason : They are treated with a divalent cation in the process of making them competent.
Select the appropriate option.
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Solution
The correct option is B Both the assertion and reason are true and reason is not the correct explanation of assertion
The ability of the cell to take up foreign (extracellular) DNA from its surrounding environment is called cell competence.
The cell membrane allows only certain molecules to pass through to maintain a consistent internal environment. The cell membrane is composed of a bilayer of phospholipids. The hydrophilic heads of the phospholipids are arranged on either side and interact with the external environment. The hydrophobic tails are arranged towards the inner side, to protect them from the surrounding environment. The DNA being a hydrophilic molecule finds it difficult to pass through the hydrophobic lipid bilayer of the host cell membrane.
Moreover, both the DNA and the cell membrane are negatively charged making it difficult for DNA to pass through the cell membrane.
Addition of the divalent cations like calcium or magnesium ions have shown to cause the condensation or shrinkage of DNA molecules and the positive charge of these divalent molecules facilitates the crossing of the negatively charged cell membrane. Hence, the assertion is true as the cell has to be made competent to allow the entry of foregin DNA for transformation and treating it with divalent cation makes it competent is the correct method for the assertion, but not the correct reason behind it.
The ability of the cell to take up foreign (extracellular) DNA from its surrounding environment is called cell competence.
The cell membrane allows only certain molecules to pass through to maintain a consistent internal environment. The cell membrane is composed of a bilayer of phospholipids. The hydrophilic heads of the phospholipids are arranged on either side and interact with the external environment. The hydrophobic tails are arranged towards the inner side, to protect them from the surrounding environment. The DNA being a hydrophilic molecule finds it difficult to pass through the hydrophobic lipid bilayer of the host cell membrane.
Moreover, both the DNA and the cell membrane are negatively charged making it difficult for DNA to pass through the cell membrane.
Addition of the divalent cations like calcium or magnesium ions have shown to cause the condensation or shrinkage of DNA molecules and the positive charge of these divalent molecules facilitates the crossing of the negatively charged cell membrane. Hence, the assertion is true as the cell has to be made competent to allow the entry of foregin DNA for transformation and treating it with divalent cation makes it competent is the correct method for the assertion, but not the correct reason behind it.
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