• Understand the use of recombinant plasmids as vectors to transform bacterial cells, as demonstrated by the production of human insulin.
• Explain the role of genetically modified and transgenic organisms in agriculture to increase crop productivity and provide resistance to disease.

The production of human insulin is a key example of recombinant DNA technology. It demonstrates how plasmids can be engineered to carry human genes into bacteria, which then produce human proteins. The same techniques can also be applied to create genetically modified organisms (GMOs).

Steps Involved in Human Insulin Production

1. Gene Insertion into Plasmids:

• Two genes that code for the insulin A and B chains are inserted into two separate plasmids.
• The insertion of these genes is done using restriction enzymes, which cut the plasmid at specific sites, allowing the insulin gene to be inserted. These enzymes cut within the tetR gene, which is responsible for tetracycline resistance.
• Each insulin gene is inserted next to a β-galactosidase gene, which helps protect the insulin polypeptides from being degraded by bacterial enzymes. This gene also helps scientists detect successful insertion.

2. Transformation of Bacteria:

• The plasmids are introduced into bacteria through a process called transformation, where bacteria take up foreign DNA from their surroundings.
• However, not all bacteria will take up the plasmid, and some may take up the plasmid without the insulin gene (non-recombinant plasmid). To identify which bacteria have taken up the correct plasmids, scientists use antibiotic resistance genes for screening.

3. Screening for Successful Transformation:

• Each plasmid contains two antibiotic resistance genes: ampR (ampicillin resistance) and tetR (tetracycline resistance).
• ampR gene: This gene gives the bacteria resistance to ampicillin. After transformation, bacteria that successfully take up any plasmid (whether it is recombinant or non-recombinant) will be able to survive on plates containing ampicillin.
• tetR gene: The tetR gene gives bacteria resistance to tetracycline. However, when scientists insert the insulin gene using restriction enzymes, the tetR gene is disrupted (cut by the restriction enzymes). As a result, bacteria with the recombinant plasmid (which has the insulin gene inserted) will not survive on plates containing tetracycline.

To screen for successful transformation:

• Bacteria are grown on ampicillin plates. If they survive, they have taken up a plasmid (either recombinant or non-recombinant).
• These bacteria are then grown on tetracycline plates. Bacteria that do not grow on tetracycline have likely taken up the recombinant plasmid because the tetR gene was disrupted during the insertion of the insulin gene.
• Bacteria that grow on both ampicillin and tetracycline have taken up a non-recombinant plasmid, meaning the plasmid wasn’t successfully modified.

4. Gene Expression and Protein Production:

• Once the screening is complete, the bacteria that carry the recombinant plasmid are allowed to grow and express the insulin gene.
• The insulin polypeptides are produced as part of a fusion protein with β-galactosidase, which protects the insulin chains from degradation.

5. Purification of Insulin:

• The fusion protein is purified from the bacteria.
• The insulin polypeptides are separated from the β-galactosidase protein, and the A and B insulin chains are combined to create functional insulin.

Key Points to Remember

• Recombinant plasmids are used to carry a gene of interest, like the insulin gene, into bacteria.
• Restriction enzymes cut the plasmid at specific sites, such as within the tetR gene, allowing the insulin gene to be inserted.
• ampR and tetR genes are used to screen for bacteria that have successfully taken up the recombinant plasmid. Bacteria that survive on ampicillin but not on tetracycline have the recombinant plasmid.
• The β-galactosidase gene is used to protect the insulin polypeptides from being degraded inside the bacteria.

Why It Matters

Understanding the production of human insulin using recombinant DNA technology is essential. This process, developed in the 1970s, remains a foundational example of how genetic engineering can be applied in biotechnology and medicine. It also helps demonstrate how similar techniques are used to produce other genetically modified organisms (GMOs).

What are Genetically Modified and Transgenic Organisms?

• Genetically Modified Organisms (GMOs) are organisms whose DNA has been altered using genetic engineering to improve traits like crop yield or disease resistance.
• Transgenic Organisms are GMOs that contain genes from a different species, such as bacteria, to enhance certain traits.

Applications in Agriculture

Increasing Crop Productivity

• GM crops are engineered to grow faster and tolerate harsh conditions, such as drought-resistant crops.

Providing Resistance to Disease

• Transgenic crops, like Bt corn, are modified with a bacterial gene from Bacillus thuringiensis that produces proteins toxic to insect pests, reducing the need for pesticides. Herbicide-resistant crops like glyphosate-resistant soybeans allow farmers to control weeds without harming the crop.

Key Points

GMOs and transgenic organisms improve crop yields and provide resistance to diseases and pests. CRISPR-Cas9 is a powerful tool for precise gene editing in agriculture.