Recombinant

figure 13-5

Researchers had questions about which molecules cause blood vessels to grow. To answer these questions, they used genetic engineering to make the proteins that control blood-vessel growth in zebrafish glow green.

The techniques of DNA technology are sometimes used to modify the genome of a living cell or organism. The process of altering the genetic material of cells or organisms to allow them to make new substances is called genetic engineering. Recombinant DNA results when DNA from two different organisms is joined.

An organism with recombinant DNA is shown in Figure 13-5. To study blood vessel growth, researchers combined a jellyfish gene encoding green fluorescent protein (GFP) that glows under ultraviolet light with a zebrafish gene that is involved in blood-vessel development. They inserted the GFP/blood-vessel gene into zebrafish embryos. The fish's blood-vessel cells transcribed the recombinant DNA and made the green fluorescent proteins. As the zebrafish grew, their blood vessels glowed green, and researchers could more easily study their growth.

Cloning Vectors

A clone is an exact copy of a DNA segment, a whole cell, or a complete organism. Biologists also use the term clone as a verb, meaning to make a genetic duplicate. Researchers can clone DNA fragments by inserting them into vectors, DNAs that can replicate within a cell, usually a bacterium or yeast, and that can carry foreign DNA. When the vector carrying the foreign DNA enters bacteria and the bacteria reproduce, they grow a colony of cloned cells that includes the foreign DNA. Cloning vectors include viruses that infect bacteria and plasmids.

Bacterium

Human DNA containing gene for insulin

Cut DNA with restriction enzyme.

Cut DNA with restriction enzyme.

Q Mix the DNAs and join them together by using DNA ligase.

Bacterium

Human DNA containing gene for insulin figure 13-6

By transferring the human insulin gene into bacteria, the cells can be made to produce human insulin.

Human gene for insulin

^^ Insert the recombinant plasmid into a host bacterium.

Recombinant bacterium figure 13-6

By transferring the human insulin gene into bacteria, the cells can be made to produce human insulin.

As shown at the top left side of Figure 13-6, plasmids are small rings of DNA found naturally in some bacterial cells in addition to the main bacterial chromosome. Step O of Figure 13-6, shown twice, illustrates the first step in making recombinant DNA using a plasmid. The plasmid and the DNA of interest (in this case, human DNA containing the gene for insulin) are isolated. In step ©, again shown for both the plasmid and the human DNA, a restriction enzyme is used to cut the DNA into many fragments. Sticky ends hold the donor and plasmid DNA together until an enzyme called DNA ligase joins them permanently, shown in step ©.

In step O, the recombinant DNA plasmids, each with a different portion of the donor DNA, are transferred into bacteria. When the bacterial cells copy their own DNA, they also copy the plasmids and the donor genes the plasmids carry, as shown in step G. After the cells have grown into colonies, the bacterial colony containing the plasmid with the desired DNA is then identified by using a probe.

Probes

A probe is a strand of RNA or single-stranded DNA that is labeled with a radioactive element or fluorescent dye and that can base-pair to specific DNA, such as the donor gene in recombinant DNA. For the donor gene in Figure 13-6, the probe is mRNA for the human insulin gene. To see which of the thousands of colonies contains the desired recombinant gene, biologists transfer the DNA from the bacteria onto filter paper. When viewed under ultraviolet light or exposed to photographic film, the clone of cells bearing the donor DNA and its attached probe glows and reveals its location. Biologists can now grow more of the specific recombinant bacterial clone.

Human gene for insulin

Q Mix the DNAs and join them together by using DNA ligase.

^^ Insert the recombinant plasmid into a host bacterium.

Recombinant bacterium i

^^ Allow the bacterium to reproduce.

Diabetes Sustenance

Diabetes Sustenance

Get All The Support And Guidance You Need To Be A Success At Dealing With Diabetes The Healthy Way. This Book Is One Of The Most Valuable Resources In The World When It Comes To Learning How Nutritional Supplements Can Control Sugar Levels.

Get My Free Ebook


Post a comment