Explain how to find whether an E. coli bacterium has transformed or not when a recombinant DNA bearing ampicillin resistant gene is transferred into it. What does the ampicillin resistant gene act as in the above case?

To determine if an E. coli bacterium has been successfully transformed with a recombinant DNA plasmid containing an ampicillin resistance gene, you would perform a selection process using ampicillin.

Procedure:

1. Plate on Ampicillin Agar: After the transformation procedure (e.g., heat shock or electroporation), the E. coli cells are plated onto agar plates containing ampicillin. Ampicillin is an antibiotic that inhibits the growth of most bacteria, including E. coli.
2. Incubation: The plates are incubated under suitable conditions (temperature, humidity) to allow bacterial growth.
3. Observation: Only transformed E. coli cells, those containing the ampicillin resistance gene, will be able to survive and grow on the ampicillin-containing agar. Non-transformed cells will be killed by the antibiotic.
4. Colony Growth: The presence of bacterial colonies growing on the plate indicates successful transformation. The number of colonies provides an estimate of the transformation efficiency (the number of transformed cells per microgram of plasmid DNA used).

Role of the Ampicillin Resistance Gene:

The ampicillin resistance gene acts as a selectable marker. It allows researchers to easily distinguish between transformed (ampicillin-resistant) and non-transformed (ampicillin-sensitive) cells. The gene provides a selective advantage to only those bacteria that have taken up the plasmid containing the gene, enabling them to grow in the presence of ampicillin. This makes it possible to isolate and study only the successfully transformed cells.