The Recombinant-dna Debate

The development of the genetic-engineering techniques described in this article was greeted, over the past decade, with both excitement and alarm. The possible benefits of the techniques were obvious, but some people felt there was reason for concern. Biologists called for an evaluation of the possible hazards of this research; the result was an unprecedented national and international effort in which the public, governments and the scientific community joined to monitor research activities. New knowledge about the properties of genes and the behavior of the bacteria used in this work (usually Escherichia coli) has led to a steady lessening of these concerns and to a relaxation of the guidelines that once restricted such experiments. In retrospect, with the advantage of hindsight, the concerns about hypothetical hazards seem to have been unwarranted. We know of no adverse effects from this research. The great potential of the new techniques, both in promoting the growth of basic knowledge and in making possible the synthesis of products of direct benefit to society, is much closer to realization than seemed likely only a few years ago.

Task2. Make a report on the basis of this text.

Source: Reprinted with permission. Copyright © April 1980 by Scientific American, Inc. All rights reserved.

Task3. Read the following article and speak about the most significant developments in biochemistry in the second half of the XX century.

1979: Biochemistry

Genetics. Research on DNA (deoxyribonucleic acid) has virtually exploded during the past two years. Perhaps the most important development has been the synthesis of many new products in "bacterial factories," but there have also been surprising findings about the structure of the gene.

Recombinant DNA. Following up on their previous successes in causing cultures of the bacterium Escherichia coli to produce the hormones somatostatin and insulin, scientists have "tricked" the bacteria into producing first a rat growth hormone and then the corresponding human growth hormone (HGH). Insertion of the gene for the rat hormone into E. coli and production of the rat hormone were reported this January by a team at the University of California at San Francisco, headed by Howard M. Goodman and John D. Baxter. In July, the UCSF team and a second group headed by David Goeddel and Peter Seeburg, of Genentech Inc. in San Francisco, independently reported the production of HGH in the same strain of bacteria. Furthermore, researchers at the University of California also inserted biochemical components of the HGH gene into E. coli, which was then induced to produce a so-called fusion protein, 70 percent of which consisted of amino acids coded by the HGH gene.

These experiments should prove useful in the commercial production of significant amounts of HGH for medical purposes. HGH isolated from the pituitary gland of cadavers is used at present to treat pituitary dwarfism in about 2,000 children in the United States, but some investigators argue that as many as 5,000 more could be helped if more of the hormone were available. Some preliminary work also suggests that HGH could be useful in healing wounds and in controlling gastrointestinal bleeding, but there has not been enough available to follow up these leads.

Hormones are not the only substances that can be prepared by recombinant DNA techniques. In November 1978, a group of investigators headed by Stanley N. Cohen and Robert T. Schimke of the Stanford University Medical Center induced E. coli to produce a mouse enzyme, known as dihydrofolate reductase, that is involved in DNA metabolism. This event marked the first time that a biologically active protein was produced in bacteria by transferred mammalian genes.

In November of the same year, Paul Berg and his colleagues at Stanford University transferred a rabbit gene into cultured monkey kidney cells—the first time that recombinant DNA techniques had been used to transfer a gene from one mammalian species to another. The gene coded for one of the polypeptide chains of rabbit hemoglobin, and the monkey cells subsequently produced that subunit.

In January 1979, Thomas H. Fraser and his colleagues at the Upjohn Company, Kalamazoo, Mich., reported that they had successfully produced chicken-egg ovalbumin in E. coli. The achievement had no immediate commercial application, but it was the first demonstration that large proteins could be successfully produced in bacteria. Ovalbumin has a molecular weight of about 43,000, compared with only 6,000 for insulin.

Production of an even larger protein, with a molecular weight of 249,000, was reported in May by Arthur J. Hale and a team at the G. D. Searle and Company laboratory in High Wycombe, England. The protein is a hemagglutinin, one of the large proteins that determine the antigenic specificity of the influenza virus. The company hopes that hemagglutinins produced in bacterial culture can be used in the preparation of a new influenza vaccine. To judge from these first attempts, recombinant DNA techniques may be simpler and more versatile than anyone had previously expected.

The last few years have also seen a decline in concern that recombinant DNA research might result in possibly dangerous genic material escaping from the laboratory. In 1976 fairly strict federal guidelines had been imposed on federally funded recombinant DNA experiments. This September, however, in accord with the latest scientific thinking, a National Institutes of Health advisory committee recommended that the guidelines be relaxed substantially.

Introns. Perhaps the most surprising development in molecular biology in recent years is the discovery that the genes of higher organisms are segmented. Several teams of investigators have discovered that the DNA sequence of each gene is interrupted one or more times by "introns," or intervening sequences that seem to have no meaning in the genetic code. The gene for an egg protein known as conalbumin, for example, contains 17 introns, and some evidence indicates that less than 10 percent of the gene for the enzyme dihydrofolate reductase actually codes for the amino acids in the enzyme.

Much evidence indicates that an entire gene, including the introns, is converted into messenger RNA (ribonucleic acid). It now appears that one or more enzymes then begin at both ends of the messenger RNA to clip out the introns, splicing the remaining segments together to re-form the RNA, which can then be used as a template for the production of a protein. Postulated functions of the introns are still entirely speculative, but it is clear they must have some role, since mutations in the nucleic acid sequences of the introns have been shown to affect the function of the gene product. One possibility is that some of the introns are promoters—regions of DNA where the enzyme RNA polymerase first binds to a gene before transcribing it. Introns may also play a role in control of gene expression.

Reproductive research. Karl Ilmensee and his colleagues at the University of Geneva in Switzerland have succeeded in transferring the nuclei of cells from one strain of mice into egg cells from another strain and then growing healthy mice from the altered egg cells. If the cells had come from adult mice, this feat would have been cloning in the true sense of the word. In this case, though, the nucleus came from a cell of a blastocyst. (The blastocyst is a stage of growth in which a normal fertilized egg has divided into 64 cells.) The experiment at Geneva is the closest anyone has come to cloning mammals. Ilmensee attributes his success to a new procedure, in which a protective coating of the egg, called the zona pellucida, is left intact; in most previous work, the zona pellucida had been removed.

Cancer. Most molecular biologists have argued that cancer viruses induce tumors in animals by taking over genetic machinery in the nucleus of the host cell and that other changes in the cell are secondary to this process. A small group of investigators, however, have argued that the most important changes in the host cell occur in the cellular membranes and that it is these changes that permit unrestrained replication of the cancer cells.

Support for the latter view has now been provided by one of the chief proponents of the former view. David Baltimore and his associates at the Massachusetts Institute of Technology have found that infection of mouse cells by a leukemia virus produces a large new protein residing in the cellular membrane. The new protein is a "kinase," an enzyme that can transfer phosphate groups from adenosine triphosphate to other molecules and to itself. Other tumor viruses have also been shown to trigger production of kinases, but this is the first instance in which the protein has definitely been shown to exist in the membrane. If the viruses do promote excessive growth by effects on membranes, then the biochemistry of cancer cells might be simpler than had previously been expected.

Chlorophyll. Scientists have long thought that there are only two forms of chlorophyll, termed a and b. The two types are combined in a lipoprotein membrane of plant cells, where they cooperatively convert sunlight, water, and carbon dioxide into food. Now, however, Constantin A. Rebeiz and his colleagues at the University of Illinois have isolated three chemically distinct chlorophyll a's and two chlorophyll b's and have further evidence of at least three other a's and two other b's. Their work suggests that each of the variants has a somewhat different capacity for the conversion of sunlight to food. Rebeiz thus argues that it might be possible to breed plants containing the best variants of the chlorophylls and thereby to increase the photosynthetic efficiency of food crops.

Magnetic bacteria. Certain species of bacteria apparently have the ability to synthesize internal compasses that they use for navigation. These so-called magnetotactic bacteria were first discovered near Woods Hole, Mass., in 1975 by Richard P. Blakemore of the University of New Hampshire, who found that they consistently swam northward and downward. He cultured the bacteria in an iron-deficient medium and obtained a nonmagnetic variant of the same species. The naturally occurring magnetic bacteria were then shown to have more than ten times the iron content of the nonmagnetic variant (and of bacteria generally).

Studies by Blakemore and Richard B. Frankel of the Massachusetts Institute of Technology demonstrated that the iron in the magnetic bacteria is present primarily in the form of the inorganic mineral known as magnetite, or lodestone. They also found that the magnetite is present in particles of exactly the right size to make an effective compass and that there are enough of the particles—generally 22 to 25 strung in a line across the longitudinal axis of the bacterium—to overcome the disorienting effects of thermal energy, or Brownian motion.

Similar deposits of magnetite have recently been observed in the heads of pigeons and the abdomens of bees, where they are thought to be used in navigation. Why the bacteria have developed such a system is unknown, but Blakemore speculates that its purpose is to help them reach bottom sediments, since bacteria in water are too small to distinguish up from down readily on the basis of gravity. At Woods Hole the vertical component of the earth's magnetic field is greater than the horizontal, so that a bacterium which swims toward the north magnetic pole is also swimming downward.

Task2. Make up a report on the basis of this text.

UNIT IV

LOUIS PASTEUR

Task1. Read and translate the text about the first discoveries of the famous French chemist and biologist.

Pasteur Louis (1822-1895) is world-known French chemist and biologist, who founded the science of microbiology, proved the germ theory of disease, invented the process of pasteurization, and developed vaccines for several diseases, including rabies.

Pasteur was born in Dole on December 27, 1822 and grew up in the small town of Arbois. In 1847 he earned a doctorate at the Ecole Normale in Paris, with a focus on both physics and chemistry. Becoming an assistant to one of his teachers, he began research that led to a significant discovery. He found that a beam of polarized light was rotated to either the right or the left as it passed through a pure solution of naturally produced organic nutrients, whereas when polarized light was passed through a solution of artificially synthesized organic nutrients, no rotation took place. If, however, bacteria or other microorganisms were placed in the latter solution, after a while it would also rotate light to the right or left.

Pasteur concluded that organic molecules can exist in one of two forms, called isomers (that is, having the same structure and differing only in mirror images of each other), which he referred to as “left-handed” and “right-handed” forms. When chemists synthesize an organic compound, both of these forms are produced in equal proportions, canceling each other’s optical effects. Living systems, however, which have a high degree of chemical specificity, can discriminate between the two forms, metabolizing one and leaving the other untouched and free to rotate light.

Task2. Answer the questions.

1. When and where was Pasteur born?

2. What discovery did he make being an assistant to his teacher?

3. What is an isomer?

4. What happens when chemists synthesize an organic compound?

5. When can living systems discriminate between the two isomers?

Task3. Match the two parts of a sentence.

1. Becoming an assistant to one of his teachers … .

2. A beam of polarized light is rotated to either the right or the left as … .

3. When polarized light was passed through a solution of artificially synthesized organic nutrients … .

4. When chemists synthesize an organic compound … .

1. … it passes through a pure solution of naturally produced organic nutrients.

2. … both forms are produced in equal proportions.

3. … no rotation took place.

4. … he began research that led to a significant discovery.

Task4. Read and translate the text about Pasteur’s work on fermentation.  

After spending several years of research and teaching at Dijon and Strasbourg, Pasteur moved in 1854 to the University of Lille, where he was named professor of chemistry and dean of the faculty of sciences. This faculty had been set up partly to serve as a means of applying science to the practical problems of the industries of the region, especially the manufacture of alcoholic beverages. Pasteur immediately devoted himself to research on the process of fermentation. Although his belief that yeast plays some kind of role in this process was not original, he was able to demonstrate, from his earlier work on chemical specificity, that the desired production of alcohol in fermentation is indeed due to yeast and that the undesired production of substances (such as lactic acid or acetic acid) that make wine sour is due to the presence of additional organisms such as bacteria. The souring of wine and beer had been a major economic problem in France; Pasteur contributed to solving the problem by showing that bacteria can be eliminated by heating the starting sugar solutions to a high temperature.

Pasteur extended these studies to such other problems as the souring of milk, and he proposed a similar solution: heating the milk to a high temperature and pressure before bottling. This process is now called pasteurization.

Task5. Answer the questions.

1. When did Pasteur move to the University of Lille?

2. What had the faculty of sciences at the University of Lille been set up for?

3. How could Pasteur contribute to solving the problem of souring of wine in France?

4. What process is now called pasteurization?

Task6. Are these statements true or false? Express your point of view.

1. Pasteur’s belief that yeast plays some kind of role in the process of fermentation was original.

2. The faculty of sciences was set up to serve as a means of applying science to the practical problems of the industries of the region.

3. Lactic acid and acetic acid make wine sweet.

4. The process of cooling milk to a very low temperature is called pasteurization.

Task7. Answer the question: Do you think Pasteur made a significant contribution to applying science to practical problems? Why? Explain your point of view.

Task8. Read the text about debates about the spontaneous generation of microorganisms.

Fully aware of the presence of microorganisms in nature, Pasteur undertook several experiments designed to address the question of where these “germs” came from. Were they spontaneously produced in substances themselves, or were they introduced into substances from the environment? Pasteur concluded that the latter was always the case. His findings resulted in a fierce debate with the French biologist Felix Pouchet—and later with the noted English bacteriologist Henry Bastion—who maintained that under appropriate conditions instances of spontaneous generation could be found. These debates, which lasted well into the 1870s, although a commission of the Academie des Sciences officially accepted Pasteur’s results in 1864, gave great impetus to improving experimental techniques in microbiology.

Task9. Speak about Pasteur’s view on the origin of microorganisms.

Task10. Read the text about germ theory of disease.

 Pasteur’s work on fermentation and spontaneous generation had considerable implications for medicine, because he believed that the origin and development of disease are analogous to the origin and process of fermentation. That is, disease arises from germs attacking the body from outside, just as unwanted microorganisms invade milk and cause fermentation. This concept, called the germ theory of disease, was strongly debated by physicians and scientists around the world. One of the main arguments against it was the contention that the role germs played during the course of disease was secondary and unimportant; the notion that tiny organisms could kill vastly larger ones seemed ridiculous to many people. Pasteur’s studies convinced him that he was right, however, and in the course of his career he extended the germ theory to explain the causes of many diseases.

Task11. Answer the questions.

1. Why did Pasteur’s work on fermentation and spontaneous generation have considerable implications for medicine?

2. Why was germ theory of disease strongly debated by physicians and scientists?

3. What convinced Pasteur that he was right?

Task12. Read the text about the rest of Pasteur’s life.

Pasteur spent the rest of his life working on the causes of various diseases—including septicemia, cholera, diphtheria, fowl cholera, tuberculosis, and smallpox—and their prevention by means of vaccination. He is best known for his investigations concerning the prevention of rabies, otherwise known in humans as hydrophobia. After experimenting with the saliva of animals suffering from this disease, Pasteur concluded that the disease rests in the nerve centers of the body; when an extract from the spinal column of a rabid dog was injected into the bodies of healthy animals, symptoms of rabies were produced. By studying the tissues of infected animals, particularly rabbits, Pasteur was able to develop an attenuated form of the virus that could be used for inoculation.

In 1885, a young boy and his mother arrived at Pasteur’s laboratory; the boy had been bitten badly by a rabid dog, and Pasteur was urged to treat him with his new method. At the end of the treatment, which lasted ten days, the boy was being inoculated with the most potent rabies virus known; he recovered and remained healthy. Since that time, thousands of people have been saved from rabies by this treatment.

Pasteur’s research on rabies resulted, in 1888, in the founding of a special institute in Paris for the treatment of the disease. This became known as the Institut Pasteur, and it was directed by Pasteur himself until he died. (The institute still flourishes and is one of the most important centers in the world for the study of infectious diseases and other subjects related to microorganisms, including molecular genetics.) By the time of his death in Saint-Cloud on September 28, 1895, Pasteur had long since become a national hero and had been honored in many ways. He was given a state funeral at the Cathedral of Notre Dame, and his body was placed in a permanent crypt in his institute.

Task13. Answer the questions.

1. How did Pasteur spend the rest of his life?

2. Why did Pasteur conclude that the cause for rabies rests in the nerve centers of the body?

3. When was Pasteur able to develop an attenuated form of the virus that could be used for inoculation?

4. What is the treatment for hydrophobia?

5. What did Pasteur’s research on rabies result in?

6. What do you know about the Institut Pasteur?

Task14. Describe the main steps in Pasteur’s career.

Task15. Prove that Pasteur deserves being called the founder of modern microbiology.

Task16. Answer the question: Which of Pasteur’s discoveries do you consider to be the most outstanding? Why?

Task17. Work in groups. Use the following information.

Student1. You are at a scientific conference devoted to the great scientists of the 19^th century. You are especially interested in Louis Pasteur’s life. Put questions to the speaker.

Student2. You are at a scientific conference devoted to the great scientists of the 19^th century. You are especially interested in Louis Pasteur’s works. Put questions to the speaker.

Student3. You are a speaker at a scientific conference devoted to the great scientists of the 19^th century. Be ready to answer questions about Louis Pasteur.

Task18. Translate the following word combinations into English and memorize them.

• микробная природа инфекционных заболеваний

• выбирать между двумя способами

• решать проблему каким-либо образом

• процесс брожения

• производство спиртных напитков

• скисание молока

• теория самозарождения организмов

• в подходящих условиях

• болезнь шелковичных червей

• куриная холера

• спасать от бешенства

• молекулярная генетика

• центр по изучению инфекционных заболеваний

GRAMMAR SECTION

Task1. Open the brackets and use the appropriate grammar form.

In 1865, Pasteur (to summone) from Paris, where he (to become) administrator and director of scientific studies at the Ecole Normale, to come to the aid of the silk industry in southern France. The country’s enormous production of silk suddenly (to curtail) because a disease of silkworms (to reach) epidemic proportions. (to suspect) that certain microscopic objects (to find) in the diseased silkworms (and in the moths and their eggs) were disease-producing organisms, Pasteur (to experiment) with controlled breeding and (to prove) that pebrine (to be) not only contagious but also hereditary. He (to conclude) that only in diseased and living eggs was the cause of the disease maintained; therefore, selection of disease-free eggs (to be) the solution. By (to adopt) this method of selection, the silk industry (to save) from disaster.