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Ciencias Naturales Eladio Cabañero.Sección europea de ciencias naturales inglés.Enlaces por niveles y temas de ESO y Bachillerato.

DNA Technology

DNA Technology

Recombinant DNA technology refers to the techniques used to transplant genes from one living source into another where it will be expressed.

How Does it work?:

The science of DNA technology includes the use of special enzymes called restriction enzymes, DNA vectors, and the host organisms. We will take a look at each of these groups in the following section.

Restriction Enzymes:

These special enzymes were discovered in the late 1960's as naturally occurring agents in bacteria. They protect the bacterium against foreign DNA from other organisms. Invading DNA is cut into pieces and made inoperable. This process is called restriction. As with any enzyme, these are specific in the job they do. Many of them only recognize short, specific nucleotide sequences( recognition sequences) and cut at specific points within those sequences.

Recognition Sequences: are symmetric in that the same sequence of 4 to 8 nucleotides is found on both strands, but run in opposite directions. The restriction enzymes usually cut the phosphodiester bonds of both strands in a staggered manner. The result being both ends have a single stranded area called the sticky ends. It is within this space that the new piece of DNA is added, attaching to the sticky ends. See the diagram below.

These unions are temporary until the enzyme DNA ligase is added to catalyze the formation of the phosphodiester bonds.

Vectors: are used as carriers for moving DNA from test tubes into cells. Bacterial plasmids and viruses are the most widely used vectors in DNA transfer. Bacterial cells can pick up the DNA through the process of transformation.

Host Organisms: Bacteria are usually used as hosts in genetic engineering. There are several reasons why they are chosen. 1. Bacterial DNA can be easily isolated and reintroduced into bacterial cells. 2. Bacterial cultures grow quickly. Some disadvantages surface as well: 1. Bacteria, being prokaryotic, may not be able to use the information in eukaryotic genes. 2. Bacterial cells cannot make the the necessary changes in transcription to produce some eukaryotic proteins. Eukaryotic cells can also be used as hosts. Yeast cells and some plant and animal cells can be a host for foreign DNA, but it is often difficult to get such cells to take up engineered DNA.

Steps for using Bacteria and Plasmids to Clone Genes:

1. Isolation of two kinds of DNA.

2. Treatment of plasmid and foreign DNA with the same restriction enzyme.

3. Mixture of foreign DNA with clipped plasmids.

4. Addition of DNA ligase.

5. Introduction of recombinant plasmid into bacterial cells.

6. Production of multiple gene copies by gene cloning and selection process for transformed cells.

7. Final screening for transformed cells.



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