2 Gene Technologies in Our Lives

Transcription

1 CHAPTER 15 2 Gene Technologies in Our Lives SECTION Gene Technologies and Human Applications KEY IDEAS As you read this section, keep these questions in mind: For what purposes are genes and proteins manipulated? How are cloning and stem cell research related? What ethical issues arise with the uses of gene technologies? Why Do Scientists Manipulate Genes? Scientists use gene technologies to analyze and manipulate genes from organisms. The use of gene technologies to create a change in an organism s DNA is called genetic engineering. Genetic engineering often involves the transfer of genes between organisms. DNA that combines genetic material from different organisms is recombinant DNA. Organisms with recombinant DNA are called genetically modified organisms (GMOs). Scientists often create GMOs to study organisms in new ways and to improve human lives. The table below shows the uses of GMOs in different fields. Field Food crops Livestock Medicine Basic research How GMOs are used in the field Many corn and soybean crops in the U.S. are GMOs that contain a gene from bacteria. The gene makes a protein that protects the plants from insects. Scientists also genetically engineer crops to be easier to grow and to be more nutritious. Scientists genetically engineer livestock to grow faster, have more muscle, have less fat, and produce more nutritious milk. Scientists genetically engineer bacteria to rapidly produce human proteins. These human proteins can be used to treat people with genetic disorders, such as diabetes and hemophilia. Scientists can link a gene that glows to a gene they are studying. When they insert these genes into an organism, proteins from the gene they are studying will glow. This makes them easy to locate. MANIPULATING PROTEINS Scientists can also use gene technologies to control when genes make proteins and where these proteins act. The study of how proteins interact within cells is called proteomics. Scientists can use gene technologies to produce specific proteins at specific times. They manipulate proteins for medical treatment and research. READING TOOLBOX Ask Questions As you read this section, write down any questions you have. When you finish reading, talk about your questions with a partner or a small group. Together, try to figure out the answers to your questions. READING CHECK 1. Identify Name two reasons why scientists create GMOs. 2. Describe What are two possible advantages of GMO crops to farmers? Interactive Reader 159 Gene Technologies and Human Applications

2 SECTION 2 Gene Technologies in Our Lives continued Background Recall that a somatic cell is a body cell, and not a reproductive cell. Why Do Scientists Manipulate Development? A clone is a genetically identical copy of an organism or piece of genetic material. Organisms that reproduce asexually clone themselves. Scientists can clone large animals, such as the sheep shown below, using a process called somatic-cell nuclear transfer (SCNT). However, most cloned animals do not develop normally or live long Analyze Why can t the baby sheep be a clone of the sheep in step 2? 4. Infer Why are the cells of new embryos totipotent? 1 Scientists extracted somatic cells from the adult sheep being cloned. 2 Scientists also extracted egg cells from another sheep. They removed the nucleus from these cells. 3 Scientists placed a somatic cell and an empty egg cell near each other. They applied an electric shock that caused the two cells to fuse. 4 Scientists then triggered the cell to divide and begin to form an embryo. 5 Scientists implanted the embryo into a surrogate mother where it developed into a baby sheep. This sheep had the same genetic information as the sheep in step 1. A stem cell is a cell that can develop into various cell types. Totipotent stem cells can give rise to any cell type. Pluripotent stem cells can give rise to all cell types except reproductive cells. Multipotent stem cells can give rise to just a few cell types. Cells of new embryos are totipotent. Scientists use cloning and stem cell techniques to study animal development. These techniques help scientists learn how multicellular organisms develop from single cells. They also have potential for treating certain diseases. Scientists can use embryonic stem cells to create cell types to treat people with missing or damaged tissue. What Issues Arise From Gene Technologies? Human embryos are a major source of stem cells. However, there is controversy over whether stem cells from potential human babies should be used for research. Ethical concerns also surround the cloning of organisms and the use of GMOs. In some cases, the modified genes in GMOs have entered non-gmo organisms. In addition, proteins made by GMO crops can kill harmless insects. Interactive Reader 160 Gene Technologies and Human Applications

3 Section 2 Review SECTION VOCABULARY clone an organism, cell, or piece of genetic material that is genetically identical to one from which it was derived; to make a genetic duplicate genetic engineering a technology in which the genome of a living cell is modified for medical or industrial use recombinant DNA DNA molecules that are artificially created by combining DNA from different sources stem cell a cell that can divide repeatedly and can differentiate into specialized cell types 1. Describe What kind of DNA do genetically modified organisms have? 2. Apply Concepts How can genetically modified bacteria with human genes be used to treat human diseases? 3. Explain What can a stem cell do that most body cells cannot do? 4. Compare Complete the following table to illustrate the advantages and disadvantages of GMOs, cloning, and stem cell research. Technology Advantage Disadvantage GMOs GMOs improve the yield and nutrition of food crops and livestock. Cloning Most cloned animals do not develop normally or live long. Stem cell research Stem cells enable scientists to create cell types for treating individuals with missing or damaged tissue. Interactive Reader 161 Gene Technologies and Human Applications

4 CHAPTER 15 3 Gene Technologies in Detail SECTION Gene Technologies and Human Applications KEY IDEAS As you read this section, keep these questions in mind: What are the basic tools of genetic manipulation? How are these tools used in the major processes of modern gene technologies? How do scientists study entire genomes? READING TOOLBOX Define As you read this section, underline words you don t understand. When you learn what they mean, write the words and their definitions in your notebook. If you have trouble, work with a partner or in a small group. 1. Apply Concepts Would you expect there to be more DNA polymorphisms between two different people or between a person and a dog? 2. Make Connections If a sample of double-stranded DNA is denatured by heat, what can cause the single strands of DNA to hybridize? What Tools Are Used in Genetic Manipulation? Scientists use a set of basic tools to manipulate genetic material. These tools are adapted from natural processes in cells, and they rely on the chemical nature of DNA. The table describes the basic tools of genetic manipulation. Basic tool Restriction enzymes DNA polymorphisms Gel Electrophoresis Denaturation Hybridization Description Bacteria make restriction enzymes to cut DNA from invading viruses. Restriction enzymes cut DNA at specific places called restriction sites. Scientists use these restriction enzymes to cut DNA samples in specific ways. Differences between the DNA sequences of individuals are called DNA polymorphisms. A difference of just one nucleotide is a single nucleotide polymorphism. Scientists use polymorphisms to create DNA fingerprints and to compare individuals and species. DNA carries an electric charge. The process of electrophoresis uses an electric current to pull DNA fragments through a partly solid material called a gel. Shorter fragments move faster through a gel than longer fragments. Scientists use gel electrophoresis to separate DNA fragments by size. DNA is usually double-stranded. Scientists can use heat or strong chemicals to denature DNA. Denaturing splits DNA into two single strands. Scientists can hybridize, or bind, complementary single strands of DNA. Short single strands of DNA, called primers, hybridize to denatured DNA to start replication. What Are Gene Technology Processes? Gene technology processes are methods for manipulating genes. They combine the basic tools of genetic manipulation and cellular functions. The major gene technology processes are blotting, DNA sequencing, gene recombination, and polymerase chain reaction. Interactive Reader 162 Gene Technologies and Human Applications

5 SECTION 3 Gene Technologies in Detail continued BASIC TOOLS AND GENE TECHNOLOGY PROCESSES After DNA fragments have been separated by gel electrophoresis, scientists often use blotting processes. Blotting transfers fragments of DNA or RNA to a special surface. Scientists can then analyze the fragments. DNA sequencing is a process that determines the exact order of every nucleotide in a region of DNA. The process uses almost all of the basic tools of genetic manipulation. Gene recombination involves cutting out a gene with restriction enzymes and putting it into a vector, such as a plasmid. The vector is then put into a host organism where the gene is copied, or cloned. Polymerase chain reaction (PCR), shown below, also makes DNA clones. Polymerase Chain Reaction (PCR) 1 Add DNA 2 Cool to allow 3 DNA 4 Repeat the polymerase, the primers polymerase process by nucleotides, and to bind, or will then add heating and primers. Heat hybridize, to nucleotides cooling the to denature, or complementary to complete DNA. separate, the regions on the a copy of the DNA strands. original strands. original strands. Discuss With a partner or a small group, discuss the basic tools of genetic manipulation used in blotting processes. Background Recall that a plasmid is a genetic structure separate from a chromosome. 3. Identify Name two basic tools of genetic manipulation used in PCR. How Can Scientists Explore Genomes? Scientists can explore a genome at the level of species, individual, chromosome, gene, or nucleotide. The following techniques help scientists explore genomes: Scientists use bioinformatics to manage all the data in a genome. Bioinformatics is the use of computer technology in biology. It can be used to store, map, classify, and analyze genomic information. Genome mapping determines the relative positions of all the genes in an organism s genome. It determines where on a chromosome a gene is. A genetic library is a collection of many small fragments of DNA that represent all the genes in a genome. Scientists sequence genetic libraries to determine their DNA base pairs. They then sort and assemble the data. READING CHECK 4. Explain What does bioinformatics add to biology? Interactive Reader 163 Gene Technologies and Human Applications

6 Section 3 Review SECTION VOCABULARY bioinformatics the application of information technologies in biology, especially in genetics DNA polymorphisms variations in DNA sequences; can be used as a basis for comparing genomes DNA sequencing the process of determining the order of every nucleotide in a gene or genetic fragment; also referred to as gene sequencing electrophoresis the process by which electrically charged particles suspended in a liquid move through the liquid because of the influence of an electric field genetic library a collection of genetic sequence clones that represent all of the genes in a given genome genome mapping the process of determining the relative position of genes in a genome polymerase chain reaction a technique that is used to make many copies of selected segments of DNA (abbreviation, PCR) restriction enzyme an enzyme that cuts doublestranded DNA into fragments by recognizing specific nucleotide sequences and cutting the DNA at those sequences 1. List What basic tools do scientists use to manipulate genetic material? 2. Describe How are denaturation and hybridization used in PCR? 3. Explain What tool of genetic manipulation do bacteria make, and why do they make it? 4. Predict A scientist is separating three fragments of DNA by gel electrophoresis. The first fragment is 500 base pairs long, the second is 5,000 base pairs long, and the third is 1,500 base pairs long. Which fragment will move the fastest through the gel? 5. Identfiy Name three ways that bioinformatics helps scientists explore genomes. 6. Identify How can scientists determine the location of genes on a chromosome? Interactive Reader 164 Gene Technologies and Human Applications