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Independent research laboratories are not directly connected with industry or universities. Genetic engineers working at these labs receive money to support their research from endowment funds that have been donated by individuals who wish to see their wealth used for the advancement of science, or from granting agencies. Jackson Laboratory in Bar Harbor, Maine, is famous for genetic studies, particularly on mice. The Mayo Clinic and Foundation in Rochester, Minnesota, is a hospital and world-renowned research center. Salk Institute in San Diego, California, employs scientists working on cancer and immunology research.

Genetic engineers in academia, government, and industry are involved in many different research projects. These projects vary from trying to produce a protein in the laboratory, to changing the genetic characteristics of crop plants, to trying to understand how human genes interact. One of the first genetic engineering projects to seize the attention of the public was the genetic engineering of a protein called bovine (cow) growth hormone, or BGH.

Genetic Engineers Can Use Bacteria to Synthesize Human Proteins

During the early 1980s, genetic engineers at the Monsanto Corporation began to produce recombinant bovine growth hormone (rBGH) in their laboratories. Recombinant (r) bovine growth hormone is a protein that has been made by manipulating the DNA sequence (gene) that carries the instructions for, or encodes, the growth hormone protein so it can be produced in the laboratory. Hormones are substances secreted from specialized glands. Hormones travel through the bloodstream to affect their target organs. Growth hormone acts on many different organs to increase the overall size of the body.

Before the advent of genetic technologies, growth hormone was procured from the pituitary glands of slaughtered cows and then injected into live cows (Figure 7.1). The same technique has been used to obtain human growth hormone from the pituitary glands of human cadavers. When the human growth hormone is injected into humans who have a condition called pituitary dwarfism, their size increases. However, harvesting the growth hormone from the pituitary glands of cows and humans is laborious, and many cadavers are necessary to obtain small amounts of the protein.

Genetic engineers at Monsanto realized that they could produce large quantities of bovine growth hormone in the laboratory, inject dairy cows, and increase milk production, completely bypassing the less efficient surgical isolation of BGH. These scientists understood that if they were successful, Monsanto would stand to make a healthy profit from the dairy farmers who would buy the engineered growth hormone to increase milk yield. Let us examine how this recombinant protein is produced.

Producing rBGH

The first step in the production of the rBGH protein is to transfer the BGH gene from the nucleus of a cow cell into a bacterial cell. Bacteria with the BGH gene will then serve as factories to produce millions of copies of this gene and its protein product—making many copies of a gene is called cloning the gene.

The pituitary gland is the natural source of bovine hor growth hormone (BGH)

The pituitary gland is the natural source of bovine hor growth hormone (BGH)

Bovine growth hormone (BGH)

Figure 7.1 Bovine growth hormone.

Bovine growth hormone is a protein produced by the pituitary gland.

Cloning a Gene Using Bacterial Cells The following steps are involved in moving a BGH gene into a bacterial cell (Figure 7.2):

1. The gene is sliced out of the cow chromosome on which it resides by exposing the cow DNA to enzymes that cut DNA. These enzymes are

Bacterial chromosome

Plasmid

Bacterial chromosome

Plasmid

2. A plasmid from a bacterium is cut with the same restriction enzymes, creating the same "sticky ends" as the cow gene.

1. BGH gene is cut from the cow chromosome using restriction enzymes that leave "sticky ends" with specific base sequences.

2. A plasmid from a bacterium is cut with the same restriction enzymes, creating the same "sticky ends" as the cow gene.

3. The cleaved gene and plasmid are placed together in a test tube. Complementary "sticky ends" fit together, resulting in a recombinant plasmid.

4. The recombinant plasmid is reinserted into a bacterial cell.

5. The plasmids and the bacterial cells replicate, making millions of copies of the rBGH gene.

rBGH protein

Figure 7.2 Cloning genes using bacteria. Bacteria can be used as factories for the production of human or other animal proteins.

4. The recombinant plasmid is reinserted into a bacterial cell.

5. The plasmids and the bacterial cells replicate, making millions of copies of the rBGH gene.

rBGH protein

6. The rBGH genes produce large quantities of rBGH proteins that are harvested, purified, and injected into cows to increase milk production.

Figure 7.2 Cloning genes using bacteria. Bacteria can be used as factories for the production of human or other animal proteins.

Media Activity 7.1A Creation of a Recombinant Plasmid called restriction enzymes and act like highly specific molecular scissors. Individual restriction enzymes only cut DNA at specific sequences, such as:

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