Question

How are cells containing recombinant DNA selected?

Short answer

Cells containing recombinant DNA are selected through a process involving antibiotic resistance. Recombinant plasmids contain an antibiotic resistance gene. During the process of transformation, these plasmids are introduced into bacteria and the bacteria are then grown on a medium containing an antibiotic. The bacteria that survive the antibiotic treatment have taken up the recombinant plasmid and thus contain the recombinant DNA. These survivor bacteria are the ones that are selected.

Step-by-step solution

Understanding Recombinant DNA

Recombinant DNA is created by combining DNA sequences that would not normally occur together. In the realm of genetic engineering, it is often accomplished by splicing a gene of interest from one organism into the DNA of another, such as bacteria.

Gene Insertion

The desired gene is inserted into a plasmid – a small, circular piece of DNA – usually inside a bacterium. This forms the recombinant DNA.

Transformation Process

This recombinant DNA is then introduced into bacteria in a process called transformation. The bacteria cells take up the plasmid with the recombinant DNA.

Selection of Recombinant Cells

The bacteria are then grown on a medium containing an antibiotic. The key is that the plasmid also contains a resistance gene for this antibiotic. Therefore, only the bacteria that took up the plasmid with recombinant DNA (and thus the antibiotic resistance gene) will be able to survive in the antibiotic environment.

Identification of Recombinant Cells

The colonies of bacteria that survive the antibiotic treatment represent the cells containing recombinant DNA and can thus be selected and further used in genetic experiments.

Key concepts

Genetic Engineering

Genetic engineering is a fascinating field of science that involves modifying an organism's genetic material to achieve desirable traits or outcomes. In simpler terms, it's like writing new instructions for a living organism by altering its DNA. This process can be used for numerous purposes, including improving crop resistance to pests, producing medicines, and creating organisms that can help clean up environmental pollutants. To perform genetic engineering, scientists take advantage of certain tools:

• Restriction enzymes: These are special proteins that can cut DNA at specific sequences, similar to cutting and pasting sentences in a document.
• Ligases: Think of these as the "glue" that can link pieces of DNA together.
• Vectors: These act as delivery vehicles for transporting the new DNA into a host cell. They can be plasmids or viruses, depending on the method.

This powerful technology opens up exciting possibilities, but it also comes with ethical questions about how far we should go in altering the genetic makeup of living beings.

Plasmid Transformation

Plasmid transformation is a fundamental process in genetic engineering, where a small, circular DNA known as a plasmid is introduced into a bacterial cell. These plasmids naturally occur in bacteria and can replicate independently, making them ideal tools for genetic engineering efforts.
To understand transformation:

• The insertion: Initially, the gene of interest, such as a gene coding for a useful protein, is added to the plasmid.
• Heat shock or electroporation: These methods temporarily make the bacterial cell membranes permeable. This allows the plasmid to enter the bacterial cell.
• Recovery: After entering, the bacteria are given time to "recover" in a nutrient-rich environment, enabling them to express the new genetic information contained in the plasmid.

Once the plasmid is inside the bacteria, it can replicate and express the gene of interest, allowing for the large-scale production of certain proteins or enzymes. This process is crucial for industrial applications and research alike.

Antibiotic Resistance Selection

Antibiotic resistance selection is an essential step in identifying which bacterial cells have successfully taken up the recombinant plasmid. It plays an even more significant role in ensuring that only those with the desired traits are propagated.
Here's how it works:

• Selection marker: The plasmid used during transformation not only carries the gene of interest but also a gene conferring resistance to a specific antibiotic.
• Growth medium with antibiotics: After transformation, bacterial cells are grown on a medium or plate containing the antibiotic. Only the bacteria that have successfully incorporated the plasmid can grow and form colonies.
• Elimination of non-transformants: Bacteria without the plasmid and, consequently, the resistance gene will not survive on the antibiotic-rich medium.

This technique streamlines the process of identifying and isolating genetically modified cells, ensuring that researchers can focus on their experiments with confidence that the cells they use possess the new genetic traits they have introduced.