How can learning about DNA solve new problems?
Once scientists recognized the importance of DNA and how DNA controlled the production of proteins, they began to use this knowledge to solve new problems. One problem that scientists had to solve was how to get DNA to make protein in the laboratory. For example, the pancreas of a person who has diabetes may not make insulin. Insulin is a protein that helps the body regulate the use of sugar. Until the 1980s, a person with diabetes had to take artificial insulin that was extracted from the body of a pig. But there were problems associated with using nonhuman insulin. Now human insulin can be made in a laboratory. The production of human insulin resulted from genetic engineering.
The process of getting genes to produce their proteins in the laboratory is called genetic engineering. Genetic engineering uses the quick reproducing capabilities of certain types of cells, such as bacterial cells, to make lots of copies of certain proteins, such as insulin. To do this, the genetic engineer must put the DNA gene for the protein to be produced into the bacteria in such a way that the bacteria will duplicate it. The new genetic material in the bacteria is called recombinant DNA (or rDNA).
Bacteria are important workhorses for genetic engineering because scientists can put foreign, recombinant DNA into them. Even though bacteria are simple cells, their own genetic material is very complex. It would be very difficult to put recombinant DNA into the bacterial chromosome. But bacteria can have little circles of DNA outside of their chromosome that replicate like the chromosome replicates. These circles of DNA are called plasmids. Molecular biologists have figured out how to put (or splice) DNA from other organisms into bacterial plasmids. Then the bacteria replicate these plasmids with the inserted genes. In this way, it is possible to use bacteria to make many, many copies of a gene. Making copies of a gene in this way is called cloning.
Figure 9.1 The process for making recombinant DNA follows.
- Scientists remove DNA from a cell nucleus.
- Scientists remove plasmid DNA from a bacterium.
- The gene is cut from the DNA strand.
- Scientists cut open the plasmid.
- The cut ends of the plasmid DNA and the human DNA will attach to form a new loop of plasmid DNA, called recombinant DNA.
Scientists use special containers that have all the nutrients these bacterial cells need to grow and reproduce as quickly as possible. After the bacterial cells grow and divide many times and produce all of the proteins coded by the plasmid DNA, the scientists open the cells and remove the proteins needed, such as insulin.
The illustration below summarizes how bacteria can be used to make human insulin.
Figure 9.2 The process for making insulin through genetic engineering follows.
- Scientists remove DNA from a human cell nucleus and plasmid DNA from a bacterial cell.
- The desired gene is removed from the human DNA and recombined with plasmid DNA.
- The plasmid is put back into bacteria.
- Scientists then grow colonies of bacteria in special vessels.
- Scientists remove the desired proteins from the cells-in this case, insulin.
- The insulin is purified and, then, is available for human use.
Role-Play! Issues in Genetic Engineering.
In groups of five, discuss the following question: Does scientific research, especially in the area of genetics, always serve the best interests of people?
Each person plays one of the following roles.
- Ordinary person with little knowledge of genetics
- Person with a genetically inherited condition
- Owner of a large drug company that sells proteins such as insulin
- Elected government official, such as a senator
Decide what people's vested interests are. What helps them succeed in their jobs? For example, a geneticist depends on government funding for his or her research laboratory, and receiving that government funding depends on the geneticist's reputation for making new and important scientific discoveries. Or a government official might have many pharmaceutical companies in his or her state.
Think of a plant or a genetic condition that might be improved through DNA technology. Write a paragraph describing the improvements you might make. Also discuss some of the risks that might be involved in this genetic engineering project.
Figure 9.2 makes these processes look simple. However, consider some of the problems that geneticists had to solve to develop this technology to produce insulin. Scientists had to
- find the human gene that directs the production of insulin,
- isolate the DNA containing the insulin gene,
- put (splice) the insulin gene in a plasmid,
- insert the plasmid into the bacterium,
- get the plasmid DNA to replicate,
- get the bacterium to reproduce, and
- isolate those bacteria that have the plasmid with the human DNA.
- get the human DNA to function in the bacteria, that is, get the human DNA to replicate and produce the insulin protein.
- purify the insulin produced.
In spite of all these difficulties, recombinant DNA technology is a rapidly growing area of genetics called molecular genetics. Scientists have reproduced or are close to being able to reproduce the DNA coding for many proteins including the following.
- Insulin, the protein that controls diabetes
- Interferon, a protein that is used in cancer therapy and to prevent and/or cure certain viral diseases such as rabies, hepatitis, and herpes
- Human growth hormone
- An enzyme that breaks up protein
- Cloned anti-viral vaccines are being tested.
Scientists are also using recombinant DNA technology to improve food crops. Imagine a tomato plant that makes a protein that kills the bugs that eat it but is safe for humans. The potential for recombinant DNA technology is unlimited.
Human Genome Project
The Human Genome Project is addressing one of the most monumental problems that scientists are working on-how to locate all of the human genes in the 23 pairs of chromosomes. To solve such a huge problem, geneticists, biologists, chemists, engineers, computer scientists, mathematicians, and many others from all over the world joined together in 1989 to create the Human Genome Project. Genome is a word meaning all the DNA-genes of a species. The process of determining the location of a gene on a chromosome is called gene mapping. The current estimate is that humans have about 20,000 to 24,000 genes. It also is estimated that there are over 3 billion pairs of nucleotides that make up human DNA.
Some people might ask, “Why would scientists want to be able to locate all of the human genes?” One answer is that scientists, as human beings, are curious about nature. They are always asking why, and they want to know more. Another reason to locate all of the human genes is to improve health. There are thousands of genetic conditions that result in an illness or a handicap that are caused by single gene defects. Although some of these conditions have symptoms that can be treated, we have no way to treat the diseases themselves, let alone to cure the people who have the disease. Those working on the Human Genome Project hope that its research will enable us to learn more about genetic diseases and help lead to cures. In addition, those working on the Project believe that the research will provide tools for learning more about the causes of other human diseases including cancer, schizophrenia, and Alzheimer's disease.
You are a United States senator arguing about continued funding for the Human Genome Project. Should the project continue to receive funding? If so, should the funding be limited to certain types of research? As a government-funded project, should the project be required to make all of its findings public?
The scientists working on the Human Genome Project expect that the entire human genome will be sequenced early in the 21st century. Already the entire genome of some organisms that are simpler than humans have been sequenced. The technology that made it possible to locate, isolate, splice, and clone the gene for insulin is the same technology that is being used in the Human Genome Project.
Exactly 6,218 genes were mapped as of April 19, 1998. Most of the known genes that have been mapped are genes that cause diseases, such as sickle-cell anemia and cystic fibrosis. There is still much work to be done on mapping human genes. But the most important work still remains-figuring out what all of the estimated 20,000 to 24,000 human genes do and how they do it. Also, questions about the variations in human genes need to be addressed. After all, whose genomes are being sequenced by the Human Genome Project? How do they differ from yours?
One important fact about human genes that has been learned is that a gene is not contained in a single continuous location on a chromosome. Rather, a gene seems to have three types of nucleotide sequences. Figure 9.3 shows the three types of nucleotide sequences.
Figure 9.3 Every gene has three types of nucleotide sequences interspersed along a length of DNA. One type of nucleotide sequence is the code for a particular protein (a). Another type of nucleotide sequence, usually at the start of the gene, tells the cell whether or not to make that gene's protein (b). That is, the (b) site turns on and turns off the (a) site. The last type is nucleotides that don't seem to code for anything (c).
Gene Information Imagine it is the year 2010, and the Human Genome Project has been successful. The names and locations of all of the human genes on chromosomes are known. Discuss the following questions with a group of your classmates.
- The local hospital is offering free chromosome tests. The tests will take a day and you can learn if you have a genetic predisposition to develop cancer. Will you take the test? Why or why not?
- You also can find out which other recessive alleles (alleles for traits that are not expressed) you are carrying. Will you take this test? Why or why not?
- Would you take your children to have these tests? Why or why not? Discuss your responses with the class.
Explaining Genetics Pick one big idea from this unit and design a way to share that idea with someone who is not in your science class. You might choose a parent, since many of the things you studied were not known when your parents went to school. You might choose a younger person in your school or a sibling. Explain the idea with a cartoon, poster, or story.
Some scientists are calling the nucleotides that don't seem to code for anything “junk” DNA. But scientists are learning so much about DNA, we may someday learn that the junk DNA is doing something, may be even something important.
While the current genetic technology has helped scientists learn quite a lot about human DNA, genes, and chromosomes, it is slow, expensive, and still subject to error. The Human Genome Project itself, however, is improving the quality and precision of genetic technology.
Some people worry that the Human Genome Project will have harmful effects on human life. If we know where all the human genes are located, could parents order a human being with the variations they want, rather than allow the chromosomes with genes and alleles to sort at random (naturally)? Will knowing more about human genes and chromosomes increase tolerance for the great variety of humans or increase discrimination? As a result, one group of people in the Human Genome Project is studying the possible effects the project will have on people so we can avoid and solve potential problems.
Genetics is the study of the biological causes of genetic continuity and diversity. To learn about continuity and diversity, geneticists study how traits and variations are inherited. Some geneticists study the inheritance of traits and variations at the cellular level. These geneticists are concerned with genes, alleles, and chromosomes. Other geneticists study traits and variations at the molecular level. These geneticists are concerned with the structure and function of DNA and with protein synthesis. Some geneticists are concerned with variations that cause people to be disabled. Other geneticists study inheritance among large groups of people rather than inheritance in individual families.
As a result of their research, geneticists are able to tell us many things about the inheritance of traits and variations. The results of their research also lead to more and more unanswered questions. Genetics is an area of science that is changing very rapidly as we learn more about the human genome. Some geneticists are even studying the ethical and public policy implications of new discoveries in genetics.
Concept Map Review your notes and the key ideas from each section of the text. With a partner, choose 10 concepts that have been presented in the genetics unit. Think like a geneticist and explain how they are related. Use a concept map to display those relationships.
Activity 9-1: Biotechnology in the U.S. Senate
Participate in a Senate committee hearing on the future of biotechnology. Here is the scenario.
A molecular biologist has improved ways to clone organisms-plants, animals, and humans. Reactions from your constituents to this technology are mixed and range from support to violent opposition. The question you need to address is, “Should there be new laws that regulate gene research and genetic engineering?” You know that science, technology, politics, and ethics all come together to address this question. What will you recommend to the Senate?
Consider the following issues in determining your response.
- Will this development lead to cures for dreaded diseases such as cancer and AIDS?
- Should there be limits on genetically engineered fruits and vegetables?
- Should there be limits on cloning plants, humans, and other animals?
- How much financial support should the government provide for biotechnology research?
Conduct a Senate hearing to investigate research and applications in the field of biotechnology, specifically, genetic engineering.
- Resources on: genetics; genetic diseases; biotechnology; cloning of plants, humans, and other animals; recombinant DNA technology; gene therapy; costumes and props; and ethical opinions.
Step 1 Assign the following roles-senator, expert witnesses such as scientists involved in genetic engineering, members of the public with different opinions on the risks and benefits of genetic engineering, and scientists from companies producing genetically engineered products.
Step 2 Research your assigned role. Become an expert. You are responsible for the information necessary to ask or answer questions. Make up a name and an identity. Dress in appropriate attire.
Step 3 Participate in the Senate hearing that is set up in your class.
Step 4 Submit an opinion paper to the Senate committee at the conclusion of the hearing. The Senate committee will consider your opinions as it prepares its recommendation for the Senate.
Do you think the Human Genome Project is more likely to help or hurt humankind? Why? Defend your choice.
- What is recombinant DNA? Why is it important?
- Why are bacteria used in genetic research?
- What are five necessary steps in making recombinant DNA?
- Why is mapping human genes important to scientists' knowledge of the human genome?