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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Plasmids and Viruses as Vectors
Genetic modification is a process where scientists change an organism's DNA to give it new characteristics. It's a bit like editing the instruction manual that tells an organism how to grow and function. This technology has revolutionised medicine, agriculture and research by allowing us to create organisms with specific traits that we want.
Key Definitions:
Scientists modify genes for many reasons, including:
To modify an organism's genes, scientists need to:
Plasmids are small, circular DNA molecules found naturally in bacteria. They're separate from the main bacterial chromosome and can replicate independently. These features make them perfect tools for genetic modification.
Plasmids have several characteristics that make them ideal for genetic engineering:
Plasmids are small enough to easily move in and out of cells, but large enough to carry new genes.
They can copy themselves independently, so the new gene gets copied too when the bacteria reproduces.
Scientists can easily cut them open with restriction enzymes and insert new genes.
Here's how scientists use plasmids to transfer genes:
Before genetic modification, insulin for diabetics came from pigs and cows, which sometimes caused allergic reactions. In 1978, scientists inserted the human insulin gene into plasmids, which were then put into bacteria. These bacteria became tiny factories, producing human insulin that was safer for patients. Today, virtually all insulin is made this way, helping millions of diabetics worldwide.
Viruses are nature's gene delivery experts. They work by injecting their genetic material into cells and hijacking the cell's machinery to make more viruses. Scientists have cleverly repurposed this ability to deliver beneficial genes instead.
To turn a virus into a useful vector, scientists:
Different viruses have different advantages as vectors:
While useful, viral vectors have some drawbacks:
In 2017, the FDA approved a treatment called Luxturna for a rare form of inherited blindness. It uses a modified virus to deliver a working copy of the RPE65 gene to retinal cells. This gene produces a protein needed for vision. The treatment has restored some sight to people who were previously blind, showing the amazing potential of viral vectors in medicine.
| Feature | Plasmid Vectors | Viral Vectors |
|---|---|---|
| Size of gene that can be carried | Large (up to 10,000 base pairs) | Usually smaller (varies by virus type) |
| Ease of production | Relatively simple | More complex |
| Efficiency of gene delivery | Lower (especially in animals) | Higher |
| Safety concerns | Generally fewer | More (immune response, integration issues) |
| Main applications | Bacterial modification, protein production | Gene therapy, animal studies |
Genetic modification using vectors raises important ethical questions that scientists and society must consider:
Plasmids and viruses are powerful tools in genetic modification, each with their own strengths and limitations. Plasmids are excellent for modifying bacteria and producing proteins, while viral vectors excel at delivering genes into animal and human cells. These technologies have already revolutionised medicine and agriculture, with exciting developments continuing to emerge.
As you continue your studies, remember that genetic modification is a rapidly evolving field with enormous potential to solve global challenges, but it also requires careful consideration of safety, ethics and societal impacts.
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