How is it done?
The two main components that are required for processing genetically modified organisms are the trans-gene and the target species. The trans-gene is the gene that is transferred into the target species, which is the organism being altered. Vectors are also sometimes used in order to transfer the trans-gene into the target species.
Different Methods of Genetic Engineering
There are many methods for creating bioengineered organisms; however, the three listed below are the most common.
- Plasmid Method
- Vector Method
- Biolistic Method
What happens to the trans-gene?The trans-gene is first isolated from the original organism through restriction enzymes. Restriction enzymes, also referred to as restriction endonuclease, are used to cut the genetic material of the organism (DNA) in certain places by distinguishing particular arrangements or sequences of nucleotides in the DNA (“How are GMOs Made?”). In other words, the enzymes examine the DNA and search for recognition sequences. After identifying specific sequences, the enzymes sever the two joined strands of DNA. The purpose of trans-genes is so they can eventually be added to the DNA of the organism that being modified.
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The video discusses the function of the restriction endonuclease and it also mentions
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Plasmid Method
The plasmid method is a very common form of genetic engineering. This method uses restriction enzymes in order to remove the trans-gene from the original organism. A plasmid is a circular DNA molecule that consists of the genetic material of a bacterium (Adnan). Plasmids can be transferred between bacteria, causing the traits coded in the chromosomes found in one bacterium to be shared with another bacterium (Great Pacific Media). One of the first steps of genetic engineering is to place the respective plasmids and restriction enzymes in the same container. Restriction enzymes are also needed for the DNA of the target species to allow space for inserting the trans-gene. In the container, the enzymes cleave specific sequences from the plasmid, producing sticky ends. As displayed in Figure 1, sticky ends show that the DNA is cut so the bases have unpaired ends that are “overhanging”. The restriction enzymes also cut specific, recognizable sequences in the plasmid of the bacteria, and they cut straight through the DNA strands to form blunt ends (“Restriction Enzymes”). Therefore, blunt ends do not have unmatched base pairs like the sticky ends do.
Once dicing by the enzymes is completed, the sticky ends fit between the segments of the plasmids that were initially cut off and so the trans-gene can be connected to it. The two plasmids can fit together because the sticky ends allow the complementary bases of the plasmids to match. Complementary bases are composed of base pairs that are required between the two strands of DNA. For example adenine (A) and thymine (T) constitute a base pair, as do guanine (G) and cytosine (C). The video above, courtesy of McGraw Hill Companies, portrays the base pairs in DNA. Please click "Restriction Endonuclease Video" above to watch it.
After dicing, DNA ligase joins the DNA strands together, and this process is referred to as annealing. Figure 2 illustrates the restriction endonuclease cleaving the host plasmid at a specific site. DNA ligase then combines the trans-gene with the organism that is to be manipulated in order to make a new form of DNA, also known as the recombinant plasmid DNA. |
Vector Method
Figure 3
Vectors are used in order to carry the trans-gene from one organism to the target species. Vectors are often used to directly transfer genes into plants that are to be manipulated. Agrobacterium tumefacien, a bacterium and a plant pathogen, serves as a vector for DNA transfer. Agrobacterium contains a plasmid referred as “Ti,” which plays a significant role in genetic engineering because it contains a DNA segment from the original species (Prakash). Scientists have modified the Ti plasmid to eliminate the genes that, if expressed, can cause disease (Prakash). Since Agrobacterium tumefacien leads to Crown Galls disease, which causes tumors on plants, the plasmid is manipulated and the bacterial genes desired can be transferred into the plant that is being genetically modified in order to avoid the disease (as shown in Figure 3).
Biolistic Method
The biolistic method, also referred to as the gene-gun method, shoots the DNA that has been bioengineered into the cells of the plant (Adnan). Metal atoms are coated with DNA and shot into the plant under alteration. The atoms—usually tungsten or gold—are coated with DNA because DNA can be adhesive under particular conditions (McDonald). The particles are first sterilized, frozen, and then thawed before being coated with DNA. The particles are then mixed with the DNA through the use of centrifuges and vortex (“Gold Particle Preparation for Bombardment”). The DNA used to coat the metal atoms already contains the trans-gene from the original organism. Gene guns containing metal atoms layered with the DNA bombard the plant. This process is exemplified in Figure 4.
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Fun activity!
You can even make your own genetically modified organism by pressing the button below!
Author: Meheret Mekonnen
Edited by Joanne Cazeau and Ayesha Monga Kravetz
To Contact: [email protected]
Edited by Joanne Cazeau and Ayesha Monga Kravetz
To Contact: [email protected]