Question

Write the methods to introduce foreign DNA into host cells.

Answer 1

Hint: Foreign/passenger DNA is a DNA molecule fragment which is isolated and cloned enzymatically. On a chromosome, the gene is detected and taken out either before or after cloning.

Complete answer:
As in parental cells, the cloned foreign DNA fragment is normally expressed. Thus, depending on the objectives and scope of cloning experiments, foreign DNA fragments may be procured from a number of sources.
Cells have membranes that prevent the mere diffusion of DNA in or out. In order to insert foreign DNA into a cell, this is the initial barrier that scientists must overcome. Transduction, transformation, transfection and injection are the four ways to achieve this purpose. But scientists must prepare the foreign DNA by cutting it into smaller pieces or by using restriction enzymes to cut the DNA and insert the desired portion into a bacterial plasmid before these four methods are used.
Circular pieces of DNA that can be passed between bacteria and viruses are plasmids.

1.Viral Transduction
Transduction is the insertion via a virus of foreign DNA into a cell . Viruses are made of a protein coat within which DNA is housed. Viruses can bind to cells that are living and inject their DNA. Or as a membrane-bound vesicle, viruses can push into the host, before releasing their DNA inside the host. Using recombinant DNA technology, host cells that are then purposefully infected with viruses can insert foreign DNA.
It also packages copies of the foreign DNA into the new viruses when the virus produces more of itself in the host cell. They are now carriers of foreign DNA when these new viruses burst out of the host cell and can be used to introduce this DNA into other host cells.

2.Transformation and transfection
Transformation is a way to pick up fragments of DNA from their environment from bacterial cells.How this happens is uncertain, but what is known is that exposing the bacteria to calcium chloride followed by heat will cause the absorption of pieces of DNA.Transforming or transducing them with the DNA and then allowing them to mate is another way to introduce foreign DNA into bacteria.
Conjugation is called bacterial mating, and occurs when two bacteria exchange DNA through a tube connecting them. On eukaryotic cells, transfection can also be done, although it is also unknown the exact way in which this happens. Mixing foreign DNA with calcium phosphate in eukaryotes creates particles that fuse with the membrane of the host cell. It is believed that the host, a process called endocytosis, may engulf the particle.

3.Agrobacterium
Agrobacterium are tumor-causing bacteria, called crown galls, in plants. As sugar spills out from the wound, which the bacteria can detect, agrobacterium are attracted to plants that have been wounded or chopped up. Agrobacterium has a plasmid that includes genes that carry out the transfection of plant cells, called the Ti plasmid.
The Ti plasmid has a region called T-DNA, which is cut from the plasmid and transferred into the plant cell by bacterial proteins from the bacteria. The incorporation of foreign DNA by restriction enzymes into the T-DNA region is one way scientists insert genes into plants.

4.Injection
A common way to integrate foreign DNA into plants is to inject the DNA physically with a gene gun. The idea of a gene gun is to cover foreign DNA with microscopic particles of gold or tungsten. These particles are then loaded into the gun, which contains helium gas that is pressurised. A gas release propels the DNA-coated particles like bullets out of the gun. These particles penetrate plant cell walls and release foreign DNA that is now part of the cell of the plant.
Gene guns can be used directly from ground-up plant tissue on the leaf of a plant or on plant cells that have been isolated.

Note: We use genetic vectors to deliver foreign DNA into the receiving cells. In order to promote DNA manipulation, they can replicate autonomously and usually provide features. They are often referred to as vehicles with international DNA.