# NEET Zoology Biotechnology Principles and Processes Questions Solved

BOARD

Why has a bacterium to first become 'competent' to be able to take up DNA? Explain

how it becomes 'competent' and takes in the recombinant DNA.

DNA is a hydrophilic molecule. It cannot pass through cell membrane.

In order to force bacteria to take up the plasmid, the bacterial cells must first be

made 'competent' to take up DNA. This is done by following methods:

1. Treating cells with a specific concentration of a divalent cation such as calcium,

which increases the efficiency with which DNA enters the bacterium through pores

in its cell wall.

2. Recombinant DNA can then be forced into such cells by incubating the cells with

r-DNA on ice, followed by placing them briefly at $42°\mathrm{C}$ (heat shock) and then putting

them back on the ice. This enables the bacteria to take up the r-DNA.

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