Chapter 20 Dna Technology and Genomics Reading Guide

Biotechnology

Relying on the study of DNA, genomics analyzes entire genomes, while biotechnology uses biological agents for technological advancements.

Learning Objectives

Justify an overview of the field of biotechnology

Key Takeaways

Key Points

• Genomics includes the study of a complete set of genes, their nucleotide sequence and organization, and their interactions within a species and with other species.
• Through DNA sequencing, genomic information is used to create maps of the DNA of different organisms.
• Biotechnology, or the use of biological agents for technological progression, has applications in medicine, agriculture, and in industry, which include processes such as fermentation and the production of biofuels.

Key Terms

• genomics: the study of the complete genome of an organism
• sequencing: the procedure of determining the order of amino acids in the polypeptide chain of a protein (protein sequencing) or of nucleotides in a DNA section comprising a gene (gene sequencing)
• biotechnology: the use of living organisms (especially microorganisms) in industrial, agricultural, medical, and other technological applications

The study of nucleic acids began with the discovery of DNA, progressed to the study of genes and small fragments, and has now exploded to the field of genomics. Genomics is the study of entire genomes, including the complete set of genes, their nucleotide sequence and organization, and their interactions within a species and with other species. The advances in genomics have been made possible by DNA sequencing technology. Just as information technology has led to Google maps that enable people to get detailed information about locations around the globe, genomic information is used to create similar maps of the DNA of different organisms. These findings have helped anthropologists to better understand human migration and have aided the field of medicine through the mapping of human genetic diseases. The ways in which genomic information can contribute to scientific understanding are varied and quickly growing.

Genomics: In genomics, the DNA of different organisms is compared, enabling scientists to create maps with which to navigate the DNA of different organisms.

Another rapidly-advancing field that utilizes DNA is biotechnology. This field involves the use of biological agents for technological advancement. Biotechnology was used for breeding livestock and crops long before the scientific basis of these techniques was understood. Since the discovery of the structure of DNA in 1953, the field of biotechnology has grown rapidly through both academic research and private companies. The primary applications of this technology are in medicine (production of vaccines and antibiotics) and agriculture (genetic modification of crops, such as to increase yields). Biotechnology also has many industrial applications, such as fermentation, the treatment of oil spills, and the production of biofuels.

Basic Techniques to Manipulate Genetic Material (DNA and RNA)

Basic techniques used in genetic material manipulation include extraction, gel electrophoresis, PCR, and blotting methods.

Learning Objectives

Distinguish among the basic techniques used to manipulate DNA and RNA

Key Takeaways

Key Points

• The first step to study or work with nucleic acids includes the isolation or extraction of DNA or RNA from cells.
• Gel electrophoresis depends on the negatively-charged ions present on nucleic acids at neutral or basic pH to separate molecules on the basis of size.
• Specific regions of DNA can be amplified through the use of polymerase chain reaction for further analysis.
• Southern blotting involves the transfer of DNA to a nylon membrane, while northern blotting is the transfer of RNA to a nylon membrane; these techniques allow samples to be probed for the presence of certain sequences.

Key Terms

• denaturation: the change of folding structure of a protein (and thus of physical properties) caused by heating, changes in pH, or exposure to certain chemicals
• electrophoresis: a method for the separation and analysis of large molecules, such as proteins or nucleic acids, by migrating a colloidal solution of them through a gel under the influence of an electric field
• polymerase chain reaction: a technique in molecular biology for creating multiple copies of DNA from a sample

Basic Techniques to Manipulate Genetic Material (DNA and RNA)

To understand the basic techniques used to work with nucleic acids, remember that nucleic acids are macromolecules made of nucleotides (a sugar, a phosphate, and a nitrogenous base) linked by phosphodiester bonds. The phosphate groups on these molecules each have a net negative charge. An entire set of DNA molecules in the nucleus is called the genome. DNA has two complementary strands linked by hydrogen bonds between the paired bases. The two strands can be separated by exposure to high temperatures (DNA denaturation) and can be reannealed by cooling. The DNA can be replicated by the DNA polymerase enzyme. Unlike DNA, which is located in the nucleus of eukaryotic cells, RNA molecules leave the nucleus. The most common type of RNA that is analyzed is the messenger RNA (mRNA) because it represents the protein -coding genes that are actively expressed.

DNA and RNA Extraction

To study or manipulate nucleic acids, the DNA or RNA must first be isolated or extracted from the cells. This can be done through various techniques. Most nucleic acid extraction techniques involve steps to break open the cell and use enzymatic reactions to destroy all macromolecules that are not desired (such as degradation of unwanted molecules and separation from the DNA sample). Cells are broken using a lysis buffer (a solution that is mostly a detergent); lysis means "to split." These enzymes break apart lipid molecules in the membranes of the cell and the nucleus. Macromolecules are inactivated using enzymes such as proteases that break down proteins, and ribonucleases (RNAses) that break down RNA. The DNA is then precipitated using alcohol. Human genomic DNA is usually visible as a gelatinous, white mass. Samples can be stored at –80°C for years.

DNA Extraction: This diagram shows the basic method used for extraction of DNA.

RNA analysis is performed to study gene expression patterns in cells. RNA is naturally very unstable because RNAses are commonly present in nature and very difficult to inactivate. Similar to DNA, RNA extraction involves the use of various buffers and enzymes to inactivate macromolecules and preserve the RNA.

Gel Electrophoresis

Because nucleic acids are negatively-charged ions at neutral or basic pH in an aqueous environment, they can be mobilized by an electric field. Gel electrophoresis is a technique used to separate molecules on the basis of size using this charge and may be separated as whole chromosomes or fragments. The nucleic acids are loaded into a slot near the negative electrode of a porous gel matrix and pulled toward the positive electrode at the opposite end of the gel. Smaller molecules move through the pores in the gel faster than larger molecules; this difference in the rate of migration separates the fragments on the basis of size. There are molecular-weight standard samples that can be run alongside the molecules to provide a size comparison. Nucleic acids in a gel matrix can be observed using various fluorescent or colored dyes. Distinct nucleic acid fragments appear as bands at specific distances from the top of the gel (the negative electrode end) on the basis of their size.

Gel Electrophoresis: Shown are DNA fragments from seven samples run on a gel, stained with a fluorescent dye, and viewed under UV light.

Amplification of Nucleic Acid Fragments by Polymerase Chain Reaction

Polymerase chain reaction (PCR) is a technique used to amplify specific regions of DNA for further analysis. PCR is used for many purposes in laboratories, such as the cloning of gene fragments to analyze genetic diseases, identification of contaminant foreign DNA in a sample, and the amplification of DNA for sequencing. More practical applications include the determination of paternity and detection of genetic diseases.

PCR Amplification: Polymerase chain reaction, or PCR, is used to amplify a specific sequence of DNA. Primers—short pieces of DNA complementary to each end of the target sequence—are combined with genomic DNA, Taq polymerase, and deoxynucleotides. Taq polymerase is a DNA polymerase isolated from the thermostable bacterium Thermus aquaticus that is able to withstand the high temperatures used in PCR. Thermus aquaticus grows in the Lower Geyser Basin of Yellowstone National Park. Reverse transcriptase PCR (RT-PCR) is similar to PCR, but cDNA is made from an RNA template before PCR begins.

DNA fragments can also be amplified from an RNA template in a process called reverse transcriptase PCR (RT-PCR). The first step is to recreate the original DNA template strand (called cDNA) by applying DNA nucleotides to the mRNA. This process is called reverse transcription. This requires the presence of an enzyme called reverse transcriptase. After the cDNA is made, regular PCR can be used to amplify it.

Hybridization, Southern Blotting, and Northern Blotting

Nucleic acid samples, such as fragmented genomic DNA and RNA extracts, can be probed for the presence of certain sequences. Short DNA fragments called probes are designed and labeled with radioactive or fluorescent dyes to aid detection. Gel electrophoresis separates the nucleic acid fragments according to their size. The fragments in the gel are then transferred onto a nylon membrane in a procedure called blotting. The nucleic acid fragments that are bound to the surface of the membrane can then be probed with specific radioactively- or fluorescently-labeled probe sequences. When DNA is transferred to a nylon membrane, the technique is called Southern blotting; when RNA is transferred to a nylon membrane, it is called northern blotting. Southern blots are used to detect the presence of certain DNA sequences in a given genome, and northern blots are used to detect gene expression.

Blotting Techniques: Southern blotting is used to find a particular sequence in a sample of DNA. DNA fragments are separated on a gel, transferred to a nylon membrane, and incubated with a DNA probe complementary to the sequence of interest. Northern blotting is similar to Southern blotting, but RNA is run on the gel instead of DNA. In western blotting, proteins are run on a gel and detected using antibodies.

Molecular and Cellular Cloning

Molecular cloning reproduces the desired regions or fragments of a genome, enabling the manipulation and study of genes.

Learning Objectives

Describe the process of molecular cloning

Key Takeaways

Key Points

• Cloning small fragments of a genome allows specific genes, their protein products, and non-coding regions to be studied in isolation.
• A plasmid, also known as a vector, is a small circular DNA molecule that replicates independently of the chromosomal DNA; it can be used to provide a "folder" in which to insert a desired DNA fragment.
• Recombinant DNA molecules are plasmids with foreign DNA inserted into them; they are created artificially as they do not occur in nature.
• Bacteria and yeast naturally produce clones of themselves when they replicate asexually through cellular cloning.

Key Terms

• recombinant DNA: DNA that has been engineered by splicing together fragments of DNA from multiple species and introduced into the cells of a host
• molecular cloning: a biological method that creates many identical DNA molecules and directs their replication within a host organism
• plasmid: a circle of double-stranded DNA that is separate from the chromosomes, which is found in bacteria and protozoa

Molecular Cloning

In general, the word "cloning" means the creation of a perfect replica; however, in biology, the re-creation of a whole organism is referred to as "reproductive cloning." Long before attempts were made to clone an entire organism, researchers learned how to reproduce desired regions or fragments of the genome, a process that is referred to as molecular cloning.

Cloning small fragments of the genome allows for the manipulation and study of specific genes (and their protein products) or noncoding regions in isolation. A plasmid (also called a vector) is a small circular DNA molecule that replicates independently of the chromosomal DNA. In cloning, the plasmid molecules can be used to provide a "folder" in which to insert a desired DNA fragment. Plasmids are usually introduced into a bacterial host for proliferation. In the bacterial context, the fragment of DNA from the human genome (or the genome of another organism that is being studied) is referred to as foreign DNA (or a transgene) to differentiate it from the DNA of the bacterium, which is called the host DNA.

Plasmids occur naturally in bacterial populations (such as Escherichia coli) and have genes that can contribute favorable traits to the organism such as antibiotic resistance (the ability to be unaffected by antibiotics). Plasmids have been repurposed and engineered as vectors for molecular cloning and the large-scale production of important reagents such as insulin and human growth hormone. An important feature of plasmid vectors is the ease with which a foreign DNA fragment can be introduced via the multiple cloning site (MCS). The MCS is a short DNA sequence containing multiple sites that can be cut with different commonly-available restriction endonucleases. Restriction endonucleases recognize specific DNA sequences and cut them in a predictable manner; they are naturally produced by bacteria as a defense mechanism against foreign DNA. Many restriction endonucleases make staggered cuts in the two strands of DNA, such that the cut ends have a 2- or 4-base single-stranded overhang. Because these overhangs are capable of annealing with complementary overhangs, these are called "sticky ends." Addition of an enzyme called DNA ligase permanently joins the DNA fragments via phosphodiester bonds. In this way, any DNA fragment generated by restriction endonuclease cleavage can be spliced between the two ends of a plasmid DNA that has been cut with the same restriction endonuclease.

Molecular Cloning: This diagram shows the steps involved in molecular cloning, where regions or fragments of a genome are reproduced to allow the study or manipulation of genes and their protein products.

Recombinant DNA Molecules

Plasmids with foreign DNA inserted into them are called recombinant DNA molecules because they are created artificially and do not occur in nature. They are also called chimeric molecules because the origin of different parts of the molecules can be traced back to different species of biological organisms or even to chemical synthesis. Proteins that are expressed from recombinant DNA molecules are called recombinant proteins. Not all recombinant plasmids are capable of expressing genes. The recombinant DNA may need to be moved into a different vector (or host) that is better designed for gene expression. Plasmids may also be engineered to express proteins only when stimulated by certain environmental factors so that scientists can control the expression of the recombinant proteins.

Cellular Cloning

Unicellular organisms, such as bacteria and yeast, naturally produce clones of themselves when they replicate asexually by binary fission; this is known as cellular cloning. The nuclear DNA duplicates by the process of mitosis, which creates an exact replica of the genetic material.

Reproductive Cloning

Reproductive cloning, possible through artificially-induced asexual reproduction, is a method used to make a clone of an entire organism.

Learning Objectives

Differentiate reproductive cloning from cellular and molecular cloning

Key Takeaways

Key Points

• A form of asexual reproduction, parthenogenesis, occurs when an embryo grows and develops without the fertilization of the egg.
• In reproductive cloning, if the haploid nucleus of an egg cell is replaced with a diploid nucleus from the cell of an individual of the same species, it will become a zygote that is genetically identical to the donor.
• Reproductive cloning has become successful, but still has limitations as cloned individuals often exhibit facial, limb, and cardiac abnormalities.
• Therapeutic cloning, the cloning of human embryos as a source of embryonic stem cells, has been attempted in order to produce cells that can be used to treat detrimental diseases or defects.

Key Terms

• clone: a living organism produced asexually from a single ancestor, to which it is genetically identical
• stem cell: a primal undifferentiated cell from which a variety of other cells can develop through the process of cellular differentiation
• parthenogenesis: a form of asexual reproduction where growth and development of embryos occur without fertilization

Reproductive Cloning

Reproductive cloning is a method used to make a clone or an identical copy of an entire multicellular organism. Most multicellular organisms undergo reproduction by sexual means, which involves genetic hybridization of two individuals (parents), making it impossible to generate an identical copy or clone of either parent. Recent advances in biotechnology have made it possible to artificially induce asexual reproduction of mammals in the laboratory.

Parthenogenesis, or "virgin birth," occurs when an embryo grows and develops without the fertilization of the egg occurring; this is a form of asexual reproduction. An example of parthenogenesis occurs in species in which the female lays an egg. If the egg is fertilized, it is a diploid egg and the individual develops into a female; if the egg is not fertilized, it remains a haploid egg and develops into a male. The unfertilized egg is called a parthenogenic, or virgin, egg. Some insects and reptiles lay parthenogenic eggs that can develop into adults.

Sexual reproduction requires two cells; when the haploid egg and sperm cells fuse, a diploid zygote results. The zygote nucleus contains the genetic information to produce a new individual. However, early embryonic development requires the cytoplasmic material contained in the egg cell. This idea forms the basis for reproductive cloning. If the haploid nucleus of an egg cell is replaced with a diploid nucleus from the cell of any individual of the same species (called a donor), it will become a zygote that is genetically identical to the donor. Somatic cell nuclear transfer is the technique of transferring a diploid nucleus into an enucleated egg. It can be used for either therapeutic cloning or reproductive cloning.

The first cloned animal was Dolly, a sheep who was born in 1996. The success rate of reproductive cloning at the time was very low. Dolly lived for seven years and died of respiratory complications. There is speculation that because the cell DNA belongs to an older individual, the age of the DNA may affect the life expectancy of a cloned individual. Since Dolly, several animals (e.g. horses, bulls, and goats) have been successfully cloned, although these individuals often exhibit facial, limb, and cardiac abnormalities. There have been attempts at producing cloned human embryos as sources of embryonic stem cells. Sometimes referred to as cloning for therapeutic purposes, the technique produces stem cells that attempt to remedy detrimental diseases or defects (unlike reproductive cloning, which aims to reproduce an organism). Still, therapeutic cloning efforts have met with resistance because of bioethical considerations.

Reproductive Cloning of Dolly, the Sheep: Dolly the sheep was the first mammal to be cloned. To create Dolly, the nucleus was removed from a donor egg cell. The nucleus from a second sheep was then introduced into the cell, which was allowed to divide to the blastocyst stage before being implanted in a surrogate mother.

Genetic Engineering

In genetic engineering, an organism's genotype is altered using recombinant DNA, created by molecular cloning, to modify an organism's DNA.

Learning Objectives

Discuss how genetic engineering leads to DNA modification.

Key Takeaways

Key Points

• A genetically modified organism receives recombinant DNA generated through molecular cloning.
• Transgenic host organisms receive their foreign DNA from a different species.
• The use of recombinant DNA vectors to alter the expression of a particular gene is known as gene targeting, which is done through the addition of mutations in a gene or the exclusion of the expression of a certain gene.
• Recombinant DNA technology involves transferring a DNA fragment of interest from one organism to another by inserting it into a vector.

Key Terms

• recombinant DNA: DNA that has been engineered by splicing together fragments of DNA from multiple species and introduced into the cells of a host
• genetic engineering: the deliberate modification of the genetic structure of an organism
• genetically modified organism: an organism whose genetic material has been altered using genetic engineering techniques

Genetic Engineering

Genetic engineering is the alteration of an organism's genotype using recombinant DNA technology to modify an organism's DNA to achieve desirable traits. Recombinant DNA technology, or DNA cloning, is the process of transferring a DNA fragment of interest from one organism to a self-replicating genetic element, such as a bacteria plasmid, which is called a vector. The DNA of interest can then be propagated in another organism. The addition of foreign DNA in the form of recombinant DNA vectors generated by molecular cloning is the most common method of genetic engineering. The organism that receives the recombinant DNA is called a genetically-modified organism (GMO). If the foreign DNA that is introduced comes from a different species, the host organism is called transgenic. Bacteria, plants, and animals have been genetically modified since the early 1970s for academic, medical, agricultural, and industrial purposes. In the US, GMOs such as Roundup-ready soybeans and borer-resistant corn are part of many common processed foods.

GMO Corn: Borer-resistant corn is an example of a genetically- modified organism made possible through genetic engineering methods that allow scientists to alter an organism's DNA to achieve specific traits, such as herbicide resistance.

Gene Targeting

Although classical methods of studying the function of genes began with a given phenotype and determined the genetic basis of that phenotype, modern techniques allow researchers to start at the DNA sequence level and ask: "What does this gene or DNA element do? " This technique, called reverse genetics, has resulted in reversing the classic genetic methodology. This method would be similar to damaging a body part to determine its function. An insect that loses a wing cannot fly, which means that the function of the wing is flight. The classical genetic method would compare insects that cannot fly with insects that can fly, and observe that the non-flying insects have lost wings. Similarly, mutating or deleting genes provides researchers with clues about gene function. The methods used to disable gene function are collectively called gene targeting. Gene targeting is the use of recombinant DNA vectors to alter the expression of a particular gene, either by introducing mutations in a gene, or by eliminating the expression of a certain gene by deleting a part or all of the gene sequence from the genome of an organism.

Genetically Modified Organisms (GMOs)

Transgenic modification, adding recombinant DNA to a species, has led to the expression of desirable genes in plants and animals.

Learning Objectives

Describe how research on transgenic plants and animals aids humans.

Key Takeaways

Key Points

• Transgenic animals are those that have been modified to express recombinant DNA from another species.
• Manipulation of transgenic plants, those that have received recombinant DNA from other species, has led to the creation of species that display disease resistance, herbicide and pesticide resistance, better nutritional value, and better shelf-life.
• The thickness of a plant's cell wall makes the artificial introduction of DNA into plant cells much more challenging than in animal cells.

Key Terms

• transgenic: of or pertaining to an organism whose genome has been changed by the addition of a gene from another species; genetically modified
• genetically modified organism: an organism whose genetic material has been altered using genetic engineering techniques

Transgenic Animals

Although several recombinant proteins used in medicine are successfully produced in bacteria, some proteins require a eukaryotic animal host for proper processing. For this reason, the desired genes are cloned and expressed in animals, such as sheep, goats, chickens, and mice. Animals that have been modified to express recombinant DNA are called transgenic animals. Several human proteins are expressed in the milk of transgenic sheep and goats, while others are expressed in the eggs of chickens. Mice have been used extensively for expressing and studying the effects of recombinant genes and mutations.

Transgenic Plants

Manipulating the DNA of plants (or creating genetically modified organisms called GMOs) has helped to create desirable traits, such as disease resistance, herbicide and pesticide resistance, better nutritional value, and better shelf-life. Plants are the most important source of food for the human population. Farmers developed ways to select for plant varieties with desirable traits long before modern-day biotechnology practices were established. Plants that have received recombinant DNA from other species are called transgenic plants. Because foreign genes can spread to other species in the environment, extensive testing is required to ensure ecological stability. Staples like corn, potatoes, and tomatoes were the first crop plants to be genetically engineered.

Transgenic Plants: Corn, a major agricultural crop used to create products for a variety of industries, is often modified through plant biotechnology.

Transformation of Plants Using Agrobacterium tumefaciens

Gene transfer occurs naturally between species in microbial populations. Many viruses that cause human diseases, such as cancer, act by incorporating their DNA into the human genome. In plants, tumors caused by the bacterium Agrobacterium tumefaciens occur by transfer of DNA from the bacterium to the plant. Although the tumors do not kill the plants, they stunt the plants, which become more susceptible to harsh environmental conditions. Many plants, such as walnuts, grapes, nut trees, and beets, are affected by A. tumefaciens. The artificial introduction of DNA into plant cells is more challenging than in animal cells because of the thick plant cell wall.

Researchers used the natural transfer of DNA from Agrobacterium to a plant host to introduce DNA fragments of their choice into plant hosts. In nature, the disease-causing A. tumefaciens have a set of plasmids, called the Ti plasmids (tumor-inducing plasmids), that contain genes for the production of tumors in plants. DNA from the Ti plasmid integrates into the infected plant cell's genome. Researchers manipulate the Ti plasmids to remove the tumor-causing genes and insert the desired DNA fragment for transfer into the plant genome. The Ti plasmids carry antibiotic resistance genes to aid selection and can be propagated in E. coli cells as well.

The Organic Insecticide Bacillus thuringiensis

Bacillus thuringiensis (Bt) is a bacterium that produces protein crystals during sporulation that are toxic to many insect species that affect plants. Bt toxin has to be ingested by insects for the toxin to be activated. Insects that have eaten Bt toxin stop feeding on the plants within a few hours. After the toxin is activated in the intestines of the insects, death occurs within a couple of days. Modern biotechnology has allowed plants to encode their own crystal Bt toxin that acts against insects. The crystal toxin genes have been cloned from Bt and introduced into plants. Bt toxin has been found to be safe for the environment, non-toxic to humans and other mammals, and is approved for use by organic farmers as a natural insecticide.

Flavr Savr Tomato

The first GM crop to be introduced into the market was the Flavr Savr Tomato, produced in 1994. Antisense RNA technology was used to slow down the process of softening and rotting caused by fungal infections, which led to increased shelf life of the GM tomatoes. Additional genetic modification improved the flavor of this tomato. The Flavr Savr tomato did not successfully stay in the market because of problems maintaining and shipping the crop.

The Flavr Savr Tomato: Plant physiologist Athanasios Theologis with tomatoes that contain the bioengineered ACC synthase gene (the Flavr Savr Tomato).

Biotechnology in Medicine

From manipulation of mutant genes to enhanced resistance to disease, biotechnology has allowed advances in medicine.

Learning Objectives

Give examples of how biotechnology is used in medicine.

Key Takeaways

Key Points

• The study of pharmacogenomics can result in the development of tailor-made vaccines for people, more accurate means of determining drug dosages, improvements in drug discovery and approval, and the development of safer vaccines.
• Modern biotechnology can be used to manufacture drugs more easily and cheaply, as they can be produced in larger quantities from existing genetic sources.
• Genetic diagnosis involves the process of testing for suspected genetic defects before administering treatment through genetic testing.
• In gene therapy, a good gene is introduced at a random location in the genome to aid the cure of a disease that is caused by a mutated gene.

Key Terms

• gene therapy: any of several therapies involving the insertion of genes into a patient's cells in order to replace defective ones
• pharmacogenomics: the study of genes that code for enzymes that metabolize drugs, and the design of tailor-made drugs adapted to an individual's genetic make-up
• immunodeficiency: a depletion in the body's natural immune system, or in some component of it

Biotechnology in Medicine

It is easy to see how biotechnology can be used for medicinal purposes. Knowledge of the genetic makeup of our species, the genetic basis of heritable diseases, and the invention of technology to manipulate and fix mutant genes provides methods to treat the disease.

Pharmacogenomics is the study of how the genetic inheritance of an individual affects his/her body's response to drugs. It is a coined word derived from the words "pharmacology" and " genomics ". It is, therefore, the study of the relationship between pharmaceuticals and genetics. The vision of pharmacogenomics is to be able to design and produce drugs that are adapted to each person's genetic makeup. Pharmacogenomics results in the following benefits:

1. Development of tailor-made medicines. Using pharmacogenomics, pharmaceutical companies can create drugs based on the proteins, enzymes, and RNA molecules that are associated with specific genes and diseases. These tailor-made drugs promise not only to maximize therapeutic effects, but also to decrease damage to nearby healthy cells.

2. More accurate methods of determining appropriate drug dosages. Knowing a patient's genetics will enable doctors to determine how well the patient's body can process and metabolize a medicine. This will maximize the value of the medicine and decrease the likelihood of overdose.

3. Improvements in the drug discovery and approval process. The discovery of potential therapies will be made easier using genome targets. Genes have been associated with numerous diseases and disorders. With modern biotechnology, these genes can be used as targets for the development of effective new therapies, which could significantly shorten the drug discovery process.

4. Better vaccines. Safer vaccines can be designed and produced by organisms transformed by means of genetic engineering. These vaccines will elicit the immune response without the attendant risks of infection. They will be inexpensive, stable, easy to store, and capable of being engineered to carry several strains of pathogen at once.

Modern biotechnology can be used to manufacture existing drugs more easily and cheaply. The first genetically-engineered products were medicines designed to combat human diseases. In 1978, Genentech joined a gene for insulin with a plasmid vector and put the resulting gene into a bacterium called Escherichia coli. Insulin, widely used for the treatment of diabetes, was previously extracted from sheep and pigs. It was very expensive and often elicited unwanted allergic responses. The resulting genetically-engineered bacterium enabled the production of vast quantities of human insulin at low cost. Since then, modern biotechnology has made it possible to produce more easily and cheaply the human growth hormone, clotting factors for hemophiliacs, fertility drugs, erythropoietin, and other drugs. Genomic knowledge of the genes involved in diseases, disease pathways, and drug-response sites are expected to lead to the discovery of thousands more new targets.

Genetic Diagnosis and Gene Therapy

The process of testing for suspected genetic defects before administering treatment is called genetic diagnosis by genetic testing. Depending on the inheritance patterns of a disease-causing gene, family members are advised to undergo genetic testing. Treatment plans are based on the findings of genetic tests that determine the type of cancer. If the cancer is caused by inherited gene mutations, other female relatives are also advised to undergo genetic testing and periodic screening for breast cancer. Genetic testing is also offered for fetuses to determine the presence or absence of disease-causing genes in families with specific, debilitating diseases.

Genetic testing involves the direct examination of the DNA molecule itself. A scientist scans a patient's DNA sample for mutated sequences. There are two major types of gene tests. In the first type, a researcher may design short pieces of DNA whose sequences are complementary to the mutated sequences. These probes will seek their complement among the base pairs of an individual's genome. If the mutated sequence is present in the patient's genome, the probe will bind to it and flag the mutation. In the second type, a researcher may conduct the gene test by comparing the sequence of DNA bases in a patient's gene to a normal version of the gene.

Gene therapy is a genetic engineering technique used to cure disease. In its simplest form, it involves the introduction of a good gene at a random location in the genome to aid the cure of a disease that is caused by a mutated gene. The good gene is usually introduced into diseased cells as part of a vector transmitted by a virus that can infect the host cell and deliver the foreign DNA. More advanced forms of gene therapy try to correct the mutation at the original site in the genome, such as is the case with treatment of severe combined immunodeficiency (SCID).

Gene Therapy: Gene therapy using an adenovirus vector can be used to cure certain genetic diseases in which a person has a defective gene.

Production of Vaccines, Antibiotics, and Hormones

Biotechnological advances in gene manipulation techniques have further resulted in the production of vaccines, antibiotics, and hormones.

Learning Objectives

Discuss the methods by which biotechnology is used to produce vaccines, antibiotics, and hormones.

Key Takeaways

Key Points

• Vaccines use weakened or inactive forms of microorganisms to mount the initial immune response through the use of antigens, which are produced through use the genes of microbes that are cloned into vectors.
• Antibiotics, agents that inhibit bacterial growth or kill bacteria, are produced by cultivating and manipulating fungal cells.
• Hormones, such as the human growth hormone (HGH), can be formulated through recombinant DNA technology; for example, HGH can be cloned from a cDNA library and inserted into E. coli cells by cloning it into a bacterial vector.

Key Terms

• bactericidal: that which kills bacteria
• bacteriostatic: that which slows down or stalls bacterial growth
• antigen: a substance that binds to a specific antibody; may cause an immune response

Production of Vaccines, Antibiotics, and Hormones

Vaccines

Traditional vaccination strategies use weakened or inactive forms of microorganisms to mount the initial immune response. Modern techniques use the genes of microorganisms cloned into vectors to mass produce the desired antigen. The antigen is then introduced into the body to stimulate the primary immune response and trigger immune memory. Genes cloned from the influenza virus have been used to combat the constantly-changing strains of this virus.

Antibiotics

Antibiotics are biotechnological products that inhibit bacterial growth or kill bacteria. They are naturally produced by microorganisms, such as fungi, to attain an advantage over bacterial populations. Antibiotics are produced on a large scale by cultivating and manipulating fungal cells. Many antibacterial compounds are classified on the basis of their chemical or biosynthetic origin into natural, semisynthetic, and synthetic. Another classification system is based on biological activity. In this classification, antibiotics are divided into two broad groups according to their biological effect on microorganisms: bactericidal agents kill bacteria, and bacteriostatic agents slow down or stall bacterial growth.

Antibiotic Treatment: Assays such as the one shown help scientists understand the effects of antibiotics on bacterial species. Clear rings around the round inserts, which contain antibiotic, mean that bacteria on the plate are inhibited or killed by the compound.

Hormones

Recombinant DNA technology was used to produce large-scale quantities of human insulin (a hormone) in E. coli as early as 1978. Previously, it was only possible to treat diabetes with pig insulin, which caused allergic reactions in humans because of differences in the gene product. In recent times, human growth hormone (HGH) has been used to treat growth disorders in children. The HGH gene was cloned from a cDNA library and inserted into E. coli cells by cloning it into a bacterial vector. The bacteria was then grown and the hormone isolated, enabling large scale commercial production.

Chapter 20 Dna Technology and Genomics Reading Guide

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