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Biochemical Explaination of Bt Corn

Page history last edited by javiervromero 13 years ago

How is it Made?








How it is made

Bt corn is a type of transgenic crop because it contains a gene that has been artificially into it instead from the process of pollination. The special gene of interest that was inserted into it is called a transgene. The gene from Bacillus thuringiensis that produces the crystal toxin protein has been inserted into the D.N.A. of the corn and therefore making it poisonous to insects.

There are primarily 5 steps in creating transgenic crops like Bt corn:

Step1: Extracting the desired gene from other organism.

Step 2: cloning the desired gene of interest

Step 3: Designing the gene

Step 4: Transformation process

Step 5: Plant breeding.


Click here for an animation of the overview of Genetic Engineering in transgenic crops

Step1: Extracting the desired gene from other organism.

This step is the most limiting step in transgenic process because there is only limited information known about specific genes required to enhance the characteristics of plants. Most of the research that is now done is focused on the identification and sequencing of certain genes. Never the less isolation of a specific gene can be easily explained and understood. First of all the main tools that are involved in this process are restriction enzyme and D.N.A. ligase(www.user.rcn.com). Restriction enzymes are enzymes that recognize a specific sequence of nucleotide bases on the D.N.A. and then cleaves it a specific sequence. Each restriction enzyme is specific to a certain sequence of nucleotide bases therefore one the sequence is known for the gene then the specific restriction enzyme is used. The restriction enzymes are like scissors and then D.N.A. ligase is the glue that sticks back the ends of the nucleotide sequences. Therefore it is used after the restriction enzyme to attach the parts of the D.N.A. fragments together. The next step is to amplify the amount of D.N.A. that was obtained because a significant amount is needed to be inserted into the desired organism.

Step 2: Cloning the desired gene of interest

The desired gene that was extracted is now subject to a process called polymerase chain reaction(PCR), a method that is used to amplify the amount D.N.A. to a workable amount.  Now the D.N.A. is placed into the plasmid of the bacteria and is replicated to produce more of the D.N.A. At this point an antibiotic resistant gene is also inserted into the plasmid which allows the carrier cell to be amplified successfully through the process of transformation. The process of transformation involves the carrier cells to be placed into two medium; one that has a specific antibiotic mean the other has no antibiotic.  The bacteria is then subject to the first medium whereby it is growth is significant and then subjected to the other medium whereby only the bacteria that has the antibiotic resistant gene can grow. The bacteria that are antibiotic resistant carries the desired D.N.A. in it and therefore only that specific kind can grow, ensuring that all of the carrier bacteria will have the desired trait.


Step 3: Designing the gene

This process is necessary because the gene has to undergo several modifications for it to be effectively inserted into a plant. Below is a diagram of what parts must be added to the gene.



The promoter sequence must be added for the gene to be correctly placed into the D.N.A. of the plant. The promoter works as an on/off switch that controls when and where in the plan the gene will be expressed. The most common promoter is the CaMV35s which comes from the cauliflower mosaic virus and cause the gene to be expressed throughout the life cycle of the plant in most tissues. On the other hand other promoters are more specific and only respond in the plants during specific internal and external environment. Sometimes the cloned gene is modified so that the plant enhances production of the gene in its cells. This enhancement is done in the Bt corn, whereby the plants nucleotide G-C is replaced with the A-T nucleotide from the Bacillus thuringiensis.

The other two parts that are added onto the gene is the termination sequence and a marker gene. The termination sequence tells the cellular machinery when the end of the gene sequence has been reached. The marker genes functions are to aid in identification of plants cells that have the specific integration of the transgene. This process is necessary because only a small percentage of targeted tissue will have the transgene. The marker gene usually consists of a protein that encodes for resistance against herbicides or specific antibiotics.


Step 4: Transformation process.

Transformation in this process means the change that will be brought upon a cell through introduction of a new D.N.A. There are two method how this could be achieved and it is explained below.

·         This first method is the gene gun method where a gun is used to insert the D.N.A. This process is also known as the micro-projectile bombardment method. This gun made up of a 6” x 7” x 10” stainless steel chamber that is connected to a 2HP vacuum pump. Then the twitch is flicked on the gun, helium is released at 1000 psi and disrupts a disk about the size of a nickel. The sock way travels to another dish that has microscopic tungsten particles 1 micron in diameter which is coated with the D.N.A. molecules. These particles travel 1300 feet per second and penetrate the cells and release the D.N.A into the nucleus. It is then incorporated by the chromosomes of the plant and comes present in the D.N.A. structure of the plant. For an animation of the gene gun click here.

·         The other method is with the Agrobacterium bacteria also known as Agrobacterium tumefaciens. This bacteria is able to infect plant cells with a piece of its D.N.A. which cause tumors. Scientist have genetically engineered this bacteria so that the gene responsible for tumor is no longer present and is replaced by the gene that is to be inserted into a plant. This plasmid is activated by the plant when it is wounded because the plant then releases chemical signals that activates it. When it is activated it enters the plant through the wound and unfortunately this is not known how the D.N.A. from moves to the cytoplasm to the nucleus of the plant. This process is beneficial because a large fragment of D.N.A can be transferred effectively.

Step 5: Plant breeding

After all of the following process has occurred successfully a process known as tissue culture is used to obtain the whole plant. In this process the plant tissues are grown under controlled environment in a series of medium that contain specific nutrients and hormones. Also tests are carried out to ensure that the plants have the desired gene and to see the activity and inheritance of the gene.








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Comments (1)

javiervromero said

at 7:52 pm on Nov 16, 2008

dude tyson u there??

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