Bacterial transformation occurs when

Question

BlackTom AI · Accepted Answer

First, let's consider the fundamentals of bacterial genetic exchange mechanisms to set the stage for evaluating the options.
Option 1 states that two bacterial cells are temporarily joined and genetic material is transferred between them. This description corresponds to conjugation, not transformation, because it involves direct cell-to-cell contact (pilus), not uptake of free DNA. So this option does not define transformation.
Option 2 claims that bacterial viruses (phages) carry bacterial genes from one host to another. This is transduction, which uses bacteriophages as vectors to move DNA between cells. Since transformation does not involve viral mediation, this option is incorrect as a definition of transformation.
Option 3 asserts that all of these are examples of bacterial transformation. Since the first two options describe conjugation and transduction, this broad claim is inaccurate. Therefore, this option cannot be correct if we are defining transformation precisely.
Option 4 describes transformation as the bacterium taking up naked, foreign DNA and incorporating it into its own genome. This aligns with the classic definition of transformation, where competent cells import extracellular DNA and integrate it into their chromosome or maintain it episomally. The phrase “naked, foreign DNA” is key here, distinguishing transformation from other forms of DNA transfer.
In summary, the correct mechanism for transformation is the uptake of free DNA from the environment by competent bacteria and its incorporation into the genome, which matches option 4. The other options depict distinct horizontal gene transfer processes (conjugation and transduction) that are not transformations, and therefore are not correct definitions for transformation.

Bacterial transformation occurs when 单项选择题

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