CHAPTER 21 DNA AND BIOTECHNOLOGY

Transcription

1 CHAPTER 21 DNA AND BIOTECHNOLOGY BEHAVIORAL OBJECTIVES 1. Describe the structure of DNA including the components of nucleotides, which parts of the nucleotides are covalently bonded to form DNA, and the role of hydrogen bonds. [21.1, pp , Fig ] 2. Explain what is meant by complementary base pairing. [21.1, p.423] 3. Understand how DNA replicates. [21.1, pp , Fig. 21.5] 4. Describe the structure of RNA including the components of the monomer and which parts of the monomers are covalently bonded to form the polymer. [21.1, p.425, Fig. 21.6] 5. List the three types of RNA found in cells and their various functions. [21.1, p.425] 6. Compare and contrast DNA and RNA structurally and functionally. [21.1, p.425, Table 21.1] 7. Describe the process of transcription and translation as components of gene expression, especially describe the function of DNA, mrna, trna, ribosomes, and necessary enzymes. [21.2, p.426, Fig ] 8. Explain the phrase the genetic code is universal. [21.2, p. 426, Table 21.2] 9. Understand how messenger RNA (mrna) is processed. [21.2, pp , Fig , 21.11] 10. Understand how the cell regulates gene expression. [21.2, p.431, Fig , Table 21.3] 11. Describe the steps involved in the cloning of a gene. [21.3, pp , Fig ] 12. List and give examples of biotechnology products and biotechnology techniques. [21.3, pp , Fig ] 13. Discuss the importance of transgenic plants, bacteria, and animals. [21.3, pp ] 14. Explain the mechanisms by which chromosomes are mapped to determine the location of specific genes. [21.3, p.437, Fig ] 15. Describe a possible method for gene therapy in humans. [21.3, pp , Fig , Table 21.4] 16. Understand and use the bold-faced and italicized terms included in this chapter. [Understanding Key Terms, p.441] EXTENDED LECTURE OUTLINE 21.1 DNA and RNA Structure and Function DNA is the genetic material and is found in the chromosomes of cells. When the cell is not dividing, DNA exists as diffuse chromatin. During cell division, chromatin condenses into chromosomes. DNA Structure and Replication Nucleotides are composed of a phosphate, a sugar, and a base. DNA has the sugar deoxyribose and four different bases: adenine (A), thymine (T), guanine (G), and cytosine (C). There is comple mentary base pairing within DNA such that A always pairs with T, and G with C. The sugar-phosphate backbone forms the uprights of the DNA double helix, with the base pairs comprising the rungs of the ladder-like shape. Replication of DNA DNA replication occurs during chromosome duplication. First, hydrogen bonds between bases break, and enzymes unzip the molecule. New nucleotides move into complementary positions. New nucleotides are joined by DNA polymerase. The new DNA molecules are complete, with each parent strand serving as a template for a new strand. Thus, the duplication is semiconservative. A replication error persists as a mutation. The Structure and Function of RNA RNA (ribonucleic acid) is a single strand of nucleotides containing the sugar ribose. The base uracil (U) replaces thymine in RNA. RNA is a helper molecule in protein synthesis. Ribosomal RNA Ribosomal RNA (rrna) is formed off a DNA template in the nucleolus. It joins with proteins imported from the cytoplasm to form the subunits of ribosomes. Messenger RNA 114

2 Messenger RNA (mrna) forms off a DNA template in the nucleus and carries genetic information out to the cytoplasm for protein synthesis. Transfer RNA Transfer RNA (trna) forms off a DNA template in the nucleus and transfers amino acids to the ribosomes, where protein is synthesized. Mader VRL CD-ROM Image 0403l.jpg (Fig. 21.1) Life Science Animations VRL 2.0 Mader ESP Modules Online Image 0404l.jpg (Fig. 21.2) Image 0405l.jpg (Fig. 21.2) Image 0406l.jpg (Fig. 21.3) Image 0407l.jpg (Fig. 21.4) Image 0408l.jpg (Fig. 21.5) Image 0409l.jpg (Fig. 21.6) Transparencies 302 (Fig. 21.2) is Highly Condensed in Eukaryotic Cells Packaging Principles of Inheritance/DNA As Genetic Material/ Overview of DNA Replication Principles of Inheritance/DNA As Genetic Material/ Semiconservative Replication (Simplified) Replication Takes Many Steps Replication_1 Replication_2 Strands are Antiparallel Principles of Inheritance/DNA As Genetic Material/DNA Repair Principles of Inheritance/DNA As Genetic Material/ Two Types of DNA Repair Genetics/DNA/DNA Structure Genetics/DNA/DNA Replication 303 (Fig. 21.3) 304 (Fig. 21.4) 305 (Fig. 21.5) 306 (Fig. 21.6) 21.2 Gene Expression Genes are expressed when a protein product occurs in the cell. Structure and Function of Proteins Proteins are composed of building blocks called amino acids. Twenty amino acids are found in cell proteins. Proteins differ in the number and sequence of their amino acids, which also determine the protein s shape. Some proteins serve structural functions, and others are enzymes. The DNA Code 115

3 A gene is a sequence of DNA that codes for a protein. DNA contains a triplet code. The genetic code is universal and is used by all organisms. Transcription During transcription, the first of two steps of gene expression, DNA serves as a template for mrna. RNA polymerase joins the nucleotides. The triplet code of DNA translates to a codon of mrna. Processing mrna DNA contains exons and introns. Before mrna leaves the nucleus, the introns are excised so that only the exons are expressed. Translation During translation, the sequence of codons results in a sequence of amino acids in a protein. Translation requires three steps. During initiation, mrna binds to the ribosome. During elongation, the polypeptide is constructed, one amino acid at a time. During termination, a stop-codon sequence is reached, and the ribosome falls away from the mrna molecule. Several ribosomes (called a polyribosome) can move along one mrna molecule at a time. Review of Gene Expression DNA contains a triplet code for each amino acid. During transcription, DNA serves as a template for the formation of mrna which now has a certain sequence of codons. Messenger RNA is processed before it leaves the nucleus, during which time its introns are removed. Messenger RNA leaves the nucleus and becomes associated with a ribosome. During translation, transfer RNA molecules brings amino acids to the ribosomes and the pairing between anticodons and codons sequences the amino acids in the order originally dictated by the sequence of bases in DNA. The Regulation of Gene Expression Gene expression can be controlled in the nucleus during transcription (transcriptional control) or after transcription (posttranscriptional control) or in the cytoplasm in translational control at the ribosome or posttranslational control. Activated Chromatin For genes to function in cells, the chromosome must first decondense in the area to be transcribed. Transcription Factors DNA-binding proteins, called transcription factors, regulate gene activity during cell specialization. Mader VRL CD-ROM Image 0410l.jpg (Fig. 21.7) Life Science Animations VRL 2.0 Image 0411l.jpg (Fig. 21.8) Image 0412l.jpg (Fig. 21.9) Image 0413l.jpg (Fig ) Image 0414al.jpg (Fig ) Image 0414bl.jpg (Fig ) Image 0414cl.jpg (Fig ) Image 0414dl.jpg (Fig ) Image 0414el.jpg (Fig ) Image 0415l.jpg (Fig ) Image 0416l.jpg (Fig ) Image 0417l.jpg (Fig ) Protein Synthesis in Eukaryotes Relationship Among RNA, DNA Template and DNA Coding Strand Transcription of RNA from DNA 116

4 Life Science Animations VRL 2.0, con t. Mader ESP Modules Online Transparencies 307 (Fig. 21.7) Transcription_ 1 Transcription_2 Beginning Translation Translating a Polypeptide Setting Stage for Transcription to Begin Polyribosome Translation_1 Translation_2 Summary of Gene Expression Messenger RNA (mrna) Processing in Eukaryotes Principles of Inheritance/Control of Gene Expression/ Levels of Gene Expression Control in Eukaryotic Cells Principles of Inheritance/Control of Gene Expression/ Transcription Factors Genetics/Protein Synthesis/Gene Activity Genetics/Protein Synthesis/Transcription Genetics/Protein Synthesis/Translation Genetics/Protein Synthesis/Gene Regulation 308 (Table 21.2) 309 (Fig. 21.8) 310 (Fig. 21.9) 311 (Fig ) 312 (Fig ) 313 (Fig ) 314 (Fig ) 315 (Table 21.3) 316 (Fig Biotechnology Biotechnology uses genetic engineering to achieve the desired end. Genetic engineering allows the insertion of a foreign gene into new cells, which are then able to produce a different product. The Cloning of a Gene When many copies of the same gene are obtained, the gene is said to be cloned. Recombinant DNA Technology Recombinant DNA contains DNA from two or more different sources. A technician selects a vector that will provide a means of getting a gene into a host cell. Plasmids and also viruses can serve as vectors. A restriction enzyme cleaves the plasmid DNA and foreign DNA at a specific sequence, leaving sticky ends. The sticky ends allow foreign DNA to be inserted into plasmid DNA. DNA ligase seals the two 117

5 types of DNA together. Then the plasmid is put into a bacterial cell and many copies of the foreign DNA as the bacteria reproduce. Bacteria do not have the enzymes to process mrna but reverse transcriptase can be used to make a DNA copy of mature mrna one without introns. The Polymerase Chain Reaction The polymerase chain reaction can produce millions of copies of a single gene or piece of DNA. Primers on either side of the target DNA get the chain reaction going. Analyzing DNA Segments DNA can be subjected to DNA fingerprinting, that is treatment with restriction enzymes produces fragments that form a pattern when separated according to their length. Matching patterns can identify a criminal or the parent of a child. Patterns also help with medical diagnoses and tracing the evolution of humans and other species. Biotechnology Products Transgenic organisms have had a foreign gene inserted into them. From Bacteria Transgenic bacteria have been used to produce biotechnology products like insulin or t-pa, promote the health of plants, degrade wastes, produce chemicals, and help mine metals. From Plants Transgenic plants now produce biotechnology products like hormone, clotting factors, and antibodies. Some plants have been enhanced to resist pests and herbicides. From Animals Gene pharming is the use of trangenic farm animals to produce pharmaceuticals in the milk of females. There are plans to use animals to produce drugs for the treatment of cystic fibrosis, cancer, blood diseases and so forth. Cloning of Transgenic Animals Cloning of animals is now a reality. A diploid nucleus from bioengineered animal is inserted into enucleated eggs from a donor. These eggs are inserted into the uterus and when development is finished the surrogate mother gives birth to the cloned animals. The Human Genome Project The Human Genome Project has two goals: to know the sequence of genes on all the human chromosomes and to know the sequence of bases on all the human chromosomes. Then, we might be able to determine the genetic defects of individuals and give them proper treatment for any ills they might have. It used to be that the Human Genome Project was done by government sponsored labs but now pharmaceuticals companies want to sponsor specific researchers because they hope to get a head start on possible drug remedies for various genetic illnesses. Gene Therapy Gene therapy is the insertion of genetic material into human cells for the treatment of a disorder. Genetic Disorders Bone marrow stem cells are withdrawn from the body, a retrovirus is used to insert a normal gene into them, and the stem cells are returned to the body. This method of gene therapy is still experimental. There are plans to treat patients with hypercholesterolemia and cystic fibrosis. Other Illnesses Gene therapy may help produce a growth factor to help form new blood vessels during angioplasty. In vivo gene therapy may one day cure hemophilia, diabetes, Parkinson disease and AIDS. Mader VRL CD-ROM Image 0418al.jpg (Fig ) Image 0418bl.jpg (Fig ) Image 0418cl.jpg (Fig ) Image 0419l.jpg (Fig. TA21.1) 118

6 Mader VRL CD-ROM, con t. Life Science Animations VRL 2.0 Mader ESP Modules Online Case Studies Online Image 0420l.jpg (Fig ) Image 0421al.jpg (Fig ) Image 0421bl.jpg (Fig. 21A) Image 0422al.jpg (Fig ) Image 0422bl.jpg (Fig ) Image 0423l.jpg (Fig ) Image 0424l.jpg (Fig ) Image 0425l.jpg (Fig. 21B) Image 0426l.jpg (Fig. TA21.2) Transparencies 317 (Fig ) Principles of Inheritance/Biotechnology/ Cloning of a Gene Principles of Inheritance/Biotechnology/ Amplifying Specific DNA Sequence Principles of Inheritance/Biotechnology/ Polymerase Chain Reaction Principles of Inheritance/Biotechnology/PCR Principles of Inheritance/Biotechnology/ Preparation of a Genomic Library Principles of Inheritance/Biotechnology/ Ex Vivo Gene Therapy in Humans Genetics/Recombinant DNA/Technology Genetics/Recombinant DNA/Applications DNA Dragnets Transgenic Cotton Tested in India; Farmers Fear Introduction of Terminator Crops Getting Recombinant Proteins Straight from the Roots Genetically Altered Papayas Save the Harvest 318 (Fig. TA21.1) 319 (Fig ) 320 (Fig ) 321 (Fig ) 322 (Fig ) 323 (Fig. TA21.2) SEVENTH EDITION CHANGES New/Revised Text: This was chapter 20 in the previous edition. Most main sections and topics were rewritten for clarity DNA and RNA Structure and Function. Most topics in this section were rewritten for clarity Gene Expression. The DNA Code and Transcription topics were rewritten for clarity Biotechnology. Polymerase Chain Reaction was rewritten for clarity. Cloning of Transgenic Animals was updated, and the diagram (Fig ) that illustrates this procedure has been simplified for better understanding. The Human Genome Project discussion was updated to include recent achievements in that area. Gene sequencing of diseases or afflictions found on chromosome 17 is illustrated in new Figure The Gene Therapy discussion has been updated and greatly expanded. It gives new information on gene therapy treatments for cystic fibrosis and for children with SCID using bone marrow stem cells. It also discussed the possibilities for the use of gene therapy to treat other illnesses, such as hemophilia, AIDS, cancer, and heart disease. New Health Focus: Organs for Transplant New Bioethical Focus: Transgenic Plants 119

7 New/Revised Figures: 21.2 DNA location and structure; 21.9 Function of introns; Polymerase chain reaction; Genetically engineered animals; Genetic map of chromosome 17; Colors have been made consistent in all DNA/RNA illustrations. New/Revised Tables: 21.2 Some DNA Codes and RNA Codons has been expanded. STUDENT ACTIVITIES Xenotransplantation 1. Scientists have begun genetically engineering pigs to serve as organ donors for humans who need transplants. They are gradually making the organs less antigenic to humans. The main concern is that even so pig s organs might carry animal viruses into humans. (HIV is a virus that jumped from monkeys into humans.) Have students read the Health Focus Organs for Transplant. Discuss some of the fears brought out in the article. General Public s Understanding of Biotechnology 2. Students should read the Bioethical Focus, Transgenic Plants, before coming to class. Divide the class into groups. Each group is to prepare a list of true-false questions concerning biotechnology, and transgenic plants in particular. Ask student volunteers to type out the list and test their friends, family, and other students on campus. They should then report back on the public s general level of understanding about biotechnology. The Promise of Biotechnology 3. Ask students to read Introduction: The Biotech Century (Time, January 11, 1999, page 42). Then have them read Leon Jaroff s Fixing the Genes (pp.68-73) making sure they also read the sidebar article on pp titled Success Stories ). [Ask the library to hold this issue on reserve or make copies of these articles for your students to use.] Use these to generate a discussion on gene therapy, its future and our concerns. 120