Genetic Engineering

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Genetic engineering is the artificial alteration or manipulation of genes.

This involves cutting a section of DNA from one organism and inserting it into the DNA of another organism.
The altered DNA is called recombinant DNA (cutting and pasting).
If the DNA is transferred between different species, the recipient organism is called transgenic.

Process of Genetic Engineering

An easy way to remember the steps is:

I _C_aught _L_eprosy _T_hrough _C_areless _E_xperimentation:

Isolation
Cutting & Ligation
Transformation
Cloning
Expression

1. Isolation

Isolation is the process of removing DNA from a cell.
To isolate the DNA, detergent is used to break down the lipid membrane.
Protease breaks down proteins surrounding the DNA.

2. Cutting & Ligation

Cutting is the removal of a gene from a piece of DNA using restriction enzymes.
- The DNA is cut open to remove the desired gene.
- A gene is also cut from the host organism, such as bacteria, using restriction enzymes.
Ligation:
- The desired gene is then inserted into the plasmid (a circular piece of bacterial DNA), which acts as a vector.
- Bacterial plasmids are commonly used as vectors in genetic engineering. A plasmid is a circular piece of DNA found in most bacterial cells.
- DNA ligase, an enzyme, joins the cut ends of the gene with the cut ends of the vector DNA.
- The resulting piece of DNA, combining the desired gene and a plasmid, is called recombinant DNA.

3. Transformation

Transformation is the uptake of recombinant DNA into a bacterial cell.
Bacterial cells are specially treated to take in plasmids.
Only some bacterial cells successfully incorporate a plasmid.

4. Cloning

Cloning is the production of identical copies of a cell.
Bacterial cells are grown on agar containing an antibiotic to identify those with plasmids. Only cells with plasmids can grow.
These bacteria reproduce, increasing the number of plasmids.
Many colonies of bacteria grow on the agar. The ones that contain a plasmid with the target gene are identified using a radioactive probe.
Once these bacterial cells are identified, they are removed and grown (cloned) on fresh agar.

5. Expression

Expression is the stimulation of a cell to produce a product of a particular gene.
- i.e. expression is the process where the host cell produces the product of the inserted gene.
The host organism grows and contains the new gene sequence from the desired organism.

Summary

Step	Purpose	Process
1. Isolation	Remove DNA from a cell	• Use detergent to break down the cell membrane. • Add protease to break down proteins around the DNA.
2. Cutting and Ligation	Remove and insert a desired gene	• Cut open DNA and the host organism's DNA using restriction enzymes. • Use the same enzyme to cut open plasmid DNA. • DNA ligase joins the gene with the plasmid, forming recombinant DNA.
3. Transformation	Introduce recombinant DNA into a bacterial cell	• Treat bacterial cells to take in plasmids. • Only some cells will successfully incorporate the plasmid.
4. Cloning	Produce identical copies of cells containing the plasmid	• Grow cells on agar with an antibiotic; only plasmid-containing cells survive. • Identify target gene colonies with a radioactive probe. • Clone these cells on fresh agar.
5. Expression	Make the host organism produce the new gene's product	• The host grows and uses the new gene sequence to produce the desired product.

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Breaking It Down

If you're finding this process difficult to understand, don't worry—it's a challenging and abstract concept! Here's a simple analogy to help you understand the core ideas. Once you understand the basic process, the scientific terms and details will become much easier to learn.

Imagine that DNA is like a recipe book, and each gene is a recipe for making something, like a cake or cookies. Sometimes, we want to improve a recipe or use it to make something completely new. Genetic engineering is like copying a recipe from one book and pasting it into another to create the desired dish.

Isolation: Finding the Recipe You Need

Analogy: You open a recipe book (the DNA of an organism) and find the specific recipe you need (the gene).
You copy the recipe onto a piece of paper.
Reality: Scientists "isolate" the gene they need from the DNA of an organism.

Cutting and Ligation: Cutting and Combining Recipes

Analogy: You carefully cut the recipe out of the original book with scissors (restriction enzymes).
Then, you paste it into another cookbook (the plasmid) using tape (DNA ligase).
Now the new cookbook has both the old recipes and the new one you added.
Reality: Scientists cut the DNA using restriction enzymes and attach it to a plasmid with DNA ligase to form recombinant DNA.

Transformation: Giving the Cookbook to a Chef

Analogy: You hand the modified cookbook (plasmid) to a chef (the bacterial cell).
The chef now has the recipe to create your special dish.
Reality: Scientists introduce the recombinant DNA into bacterial cells, which will now use it to make the desired product.

Cloning: Making Lots of Copies of the Recipe

Analogy: The chef makes many copies of the new cookbook so all their assistants can use the recipe and prepare the same dish.
Reality: The bacterial cells divide and multiply, making copies of themselves, and each contains the new gene.

Expression: Cooking the Dish

Analogy: The chefs in the kitchen follow the recipe in the cookbook to bake the cake or cookies (produce the desired product).
Reality: The bacterial cells use the new gene to produce the desired protein or product.

Genetic Engineering Simplified Revision Notes for Leaving Cert Biology