Lesson 9 of 11 · 6 min
Inserting DNA and getting the product
NCERT §9.3.4, §9.3.5
Kavya spreads her transformed E. coli on plates containing ampicillin and leaves them overnight. In the morning only a few dozen colonies have grown, and that is good news.
The lesson in notes
In short
Recipient cells made competent take up DNA from their surroundings.
If recombinant DNA carrying an ampicillin-resistance gene enters E. coli, those cells become ampicillin-resistant.
Spread on agar plates containing ampicillin, only the transformants grow and untransformed cells die. The ampicillin-resistance gene here is the selectable marker.
Inside a bacterial, plant or animal cell, the foreign DNA in the vector is multiplied. Usually the final aim is a desirable protein, so the gene must be expressed, and it is expressed under suitable conditions.
A protein made when a gene is expressed in a heterologous host is a recombinant protein.
After the gene is cloned and expression is optimised, production is scaled up. Small laboratory cultures can be used to extract the protein and purify it by separation techniques.
In a continuous culture system, spent medium drains out on one side as fresh medium flows in on the other. Cells stay in their most active log (exponential) phase, giving more biomass and a higher yield of protein.