In this lesson, we’ll explore the process of transformation of cells.
Keep reading to find out what transformation is, how it was discovered, and how it can potentially be used in gene therapy. After the lesson, take a short quiz to see what you’ve learned.
What Is Transformation?
In the 1986 movie The Fly, scientist Seth Brundle created the creature Brundlefly after accidentally mixing his own DNA with the DNA of a housefly. In reality, the transformation of an organism isn’t that fantastical.
But scientists have manipulated the ability of cells to take in foreign DNA to do some pretty amazing things.Transformation is the development of new genetic traits after it’s taken in foreign DNA. Transformation happens when bacteria take up DNA from the environment and then convert the genes encoded by the DNA into a protein or trait that can be observed. Bacteria have one circular genomic chromosome, but some bacteria have extra DNA called plasmids. Foreign DNA can be inserted on a plasmid or onto the genomic chromosome.
Why Does It Work?
Plasmids have features that allow the genes located on them to be copied and expressed as traits. A promoter is a sequence that marks the beginning of a gene and binds the necessary enzymes for transcription, or converting DNA into RNA.
Once the sequence is converted into RNA, it can be translated into a trait, or protein. If the foreign DNA is inserted into the chromosome, it will be copied and translated in the same way any other gene would be, as long as it’s near a promoter.The origin of replication is another feature found on plasmids. This is a short sequence of DNA that allows the plasmid DNA to be copied. Cells copy their DNA when they are ready to divide into two cells or for reproductive purposes. Having an origin of replication ensures that the plasmid will be copied. Regardless of whether the DNA is on a plasmid or integrated into the genome, the foreign DNA gives the bacteria new genes.
The new genes give the bacterial cell new traits when the DNA sequences are transcribed and translated.One of the reasons for antibiotic resistance in bacteria that cause human disease is the fact that bacteria are able to take up DNA from their surroundings and translate them into a new trait. Think of the human gut as a really cool bar where bacteria like to hang out because of the free nutrients.
Since there many bacteria in the human gut, it’s easy for bacteria to obtain plasmids that harbor resistance to antibiotics.In order for a bacterial cell to undergo transformation, it has to be competent. A competent cell is one that has the ability to take up foreign DNA from the environment. There are several theories describing how bacteria become competent, but the end result of all of them is that the cell becomes permeable to DNA. If the cell doesn’t receive the proper cues, it won’t take up foreign DNA into the plasma membrane.
How to Force Transformation
Bacteria are the only cells that undergo natural transformation, so there is no need to worry about your cells becoming transformed from random bits of DNA in the environment.
However, using molecular biology techniques, many cells can be transformed. Scientists have several techniques that can be used to transform cells in the lab. Each of these techniques forces the cell to become competent and take up DNA.
Some cells can be made competent by treating them with chemicals, such as calcium or magnesium chloride, and heating them. DNA will enter the cell through the weakened membrane. The use of chemicals to make cells competent can only be used to transform single-celled organisms or cell culture.
Electroporation is a technique that uses an electrical pulse to force cells to take up DNA. Like chemical techniques, it’s limited to cells that can be cultured in the lab.
Also known as biolistic particle delivery systems, gene guns are tools that use DNA gold-coated particles to mechanically deliver foreign DNA into the nucleus by shooting the cell. Originally, this method was used for the genetic modification of plants, but it can be used on cultured cells as well.
The advantage of the gene gun is that it can be used on whole organisms, and not just cultured cells. The use of gene guns in humans and other animals is still experimental, but recently scientists were able to use a gene gun to change the skin color in living rats. The use of gene guns to deliver DNA vaccines in humans is promising. These vaccines would work by making transformed cells in your body produce a protein that would give an immune response to protect you from an infectious disease. The gene gun is a bit like the hypospray from the Star Trek series. It delivers medication without the use of needles.
The microinjection technique of transforming cells uses a microscopic needle to introduce foreign DNA into the nucleus.
In multicellular organisms, including humans, microinjection is usually done shortly after fertilization. This procedure is used to create genetically modified animals that can pass on an introduced trait to future progeny because the foreign gene will be present in every cell of the body.
Some viruses have the ability to insert themselves into the genome of the cells that they infect. HIV and herpes virus infections last for the person’s life because once a person is infected, the viruses will insert their genes into the person’s genome. Scientists have modified viruses in a way that the virus will insert the desired DNA instead.
Once inserted, the infected cells of the organism contain a copy of the foreign gene, and the cells are considered transformed. Like the other potential methods of delivering foreign genes into humans, the use of viruses is still experimental.
Transformation happens when cells take in foreign DNA and express the genes encoded on that DNA. The expression of the genes gives the cell new characteristics, literally transforming the cell. Bacteria can undergo natural transformation, but the cells from other organisms can only be transformed in the lab using chemical competency, electric shock, gene guns, microinjection or viral infection.
Transformation is the idea behind human gene therapy. If scientists can safely and effectively deliver healthy genes to cells, cells harboring genetic defects can be transformed into healthy cells.