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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Recombinant DNA Transfer
Genetic modification is a technology that allows scientists to change an organism's DNA by adding genes from other organisms. This creates recombinant DNA - genetic material formed by combining DNA from different sources. It's a bit like cutting and pasting text from different documents to create something new!
Key Definitions:
Scientists modify genes to create organisms with useful characteristics. For example, crops can be made resistant to pests or diseases, bacteria can produce human insulin and plants can be engineered to grow in harsh conditions. This technology has revolutionised medicine, agriculture and research.
The first genetically modified organism was created in 1973 when scientists Herbert Boyer and Stanley Cohen successfully transferred a gene from one bacterium to another. By 1982, the first GM medicine (insulin) was approved and by 1994, the first GM food (the Flavr Savr tomato) hit supermarket shelves.
To transfer genes between organisms, scientists need special molecular tools. These work like scissors and glue for DNA.
Restriction enzymes are proteins that cut DNA at specific sequences called recognition sites. They act like molecular scissors, creating precise cuts in the DNA double helix. Each restriction enzyme recognises and cuts at a specific sequence of nucleotides.
When restriction enzymes cut DNA, they often create "sticky ends" - short, single-stranded overhangs that can pair with complementary sequences. These sticky ends are crucial for joining different DNA fragments together.
Restriction enzymes naturally occur in bacteria as a defence mechanism against viral infections. They "restrict" viral replication by cutting up the viral DNA. Scientists have repurposed these bacterial defence tools for genetic engineering!
Once DNA has been cut with restriction enzymes, DNA ligase is used to join the fragments together. Ligase forms covalent bonds between the sugar-phosphate backbones of DNA fragments, effectively "gluing" them together into a continuous strand.
This enzyme is essential for creating recombinant DNA molecules by joining DNA from different sources. Without ligase, the cut fragments would remain separate and unstable.
Creating a genetically modified organism involves several key steps:
First, scientists isolate the gene of interest from the donor organism. This might be a gene for insulin production, pest resistance, or any other desirable trait.
Using restriction enzymes, scientists cut both the isolated gene and the vector (usually a plasmid - a small circular DNA molecule) at specific sites to create compatible ends.
DNA ligase is used to join the gene of interest to the vector, creating recombinant DNA. The sticky ends help align the fragments correctly before they're joined.
The recombinant DNA is transferred into host cells. This might be done using heat shock (for bacteria), microinjection (for animal cells), or gene guns (for plant cells).
Scientists need to identify which cells have successfully taken up the recombinant DNA. This often involves marker genes that confer antibiotic resistance or produce visible traits.
Successfully modified cells are grown to produce clones, all containing the recombinant DNA. In multicellular organisms, these modified cells develop into a transgenic organism.
Vectors are DNA molecules used to carry foreign genetic material into a cell. The most common vectors include:
A good vector should have multiple restriction sites (for easy insertion of genes), marker genes (to identify successful transfers) and the ability to replicate in the host cell.
Recombinant DNA technology has numerous practical applications that affect our daily lives:
Recombinant DNA technology has revolutionised medicine by enabling the production of:
GM crops have been developed with various beneficial traits:
Before genetic engineering, diabetics relied on insulin extracted from pig and cow pancreases. This animal insulin sometimes caused allergic reactions and was expensive to produce. In 1982, Eli Lilly produced the first recombinant human insulin (Humulin) using E. coli bacteria.
The process involves inserting the human insulin gene into bacterial plasmids. The bacteria then act as tiny factories, producing human insulin that is chemically identical to what our bodies make. This revolutionised diabetes treatment, making insulin more widely available, more affordable and reducing allergic reactions.
While genetic modification offers many benefits, it also raises important ethical questions:
Recombinant DNA technology has transformed medicine, agriculture and research. By understanding how to cut, paste and transfer genes between organisms, scientists can create solutions to some of our biggest challenges - from disease treatment to food security.
However, with this powerful technology comes responsibility. As genetic modification becomes more sophisticated, society must balance innovation with careful consideration of potential risks and ethical implications.
The field continues to evolve rapidly, with new techniques like CRISPR-Cas9 making genetic modification more precise and accessible than ever before. Understanding the basics of recombinant DNA transfer provides a foundation for appreciating these advances and participating in informed discussions about their use.
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