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Chapter 12 DNA Technology and Genomics PowerPoint Lectures for Biology: Concepts & Connections, Sixth Edition Campbell, Reece, Taylor, Simon, and Dickey Lecture by Mary C. Colavito Copyright © 2009 Pearson Education, Inc. Introduction: DNA and Crime Scene Investigations DNA evidence was used to solve a double murder in England – Showed that two murders could have been committed by the same person – Showed the innocence of someone who confessed to one of the murders – Showed the absence of a match in 5,000 men tested when the murderer persuaded another man to donate blood in his name – Showed a match with the murderer and DNA found with both victims Copyright © 2009 Pearson Education, Inc. GENE CLONING Copyright © 2009 Pearson Education, Inc. 12.1 Genes can be cloned in recombinant plasmids Genetic engineering involves manipulating genes for practical purposes – Gene cloning leads to the production of multiple identical copies of a gene-carrying piece of DNA – Recombinant DNA is formed by joining DNA sequences from two different sources – One source contains the gene that will be cloned – Another source is a gene carrier, called a vector – Plasmids (small, circular DNA molecules independent of the bacterial chromosome) are often used as vectors Copyright © 2009 Pearson Education, Inc. 12.1 Genes can be cloned in recombinant plasmids Steps in cloning a gene 1. Plasmid DNA is isolated 2. DNA containing the gene of interest is isolated 3. Plasmid DNA is treated with restriction enzyme that cuts in one place, opening the circle 4. DNA with the target gene is treated with the same enzyme and many fragments are produced 5. Plasmid and target DNA are mixed and associate with each other Copyright © 2009 Pearson Education, Inc. 12.1 Genes can be cloned in recombinant plasmids 6. Recombinant DNA molecules are produced when DNA ligase joins plasmid and target segments together 7. The recombinant DNA is taken up by a bacterial cell 8. The bacterial cell reproduces to form a clone of cells Animation: Cloning a Gene Copyright © 2009 Pearson Education, Inc. E. coli bacterium Plasmid Bacterial chromosome 1 Cell with DNA containing gene of interest Isolate plasmid Isolate DNA 2 3 Cut plasmid with enzyme DNA Gene of interest 4 Cut cell’s DNA with same enzyme Gene of interest 5 6 Recombinant DNA plasmid Combine targeted fragment and plasmid DNA Examples of gene use Add DNA ligase, which closes the circle with covalent bonds Genes may be inserted into other organisms Gene of interest 9 7 Put plasmid into bacterium by transformation Recombinant bacterium 8 Clone of cells Allow bacterium to reproduce Genes or proteins are isolated from the cloned bacterium Harvested Examples of proteins protein use may be used directly Recombinant DNA plasmid Gene of interest 7 Recombinant bacterium Put plasmid into bacterium by transformation Recombinant DNA plasmid Gene of interest 7 Put plasmid into bacterium by transformation Recombinant bacterium 8 Clone of cells Allow bacterium to reproduce Examples of gene use Genes may be inserted into other organisms Recombinant DNA plasmid Gene of interest 9 7 Put plasmid into bacterium by transformation Recombinant bacterium 8 Allow bacterium to reproduce Genes or proteins are isolated from the cloned bacterium Harvested proteins may be used directly Clone of cells Examples of protein use 12.2 Enzymes are used to “cut and paste” DNA Restriction enzymes cut DNA at specific sequences – Each enzyme binds to DNA at a different restriction site – Many restriction enzymes make staggered cuts that produce restriction fragments with single-stranded ends called “sticky ends” – Fragments with complementary sticky ends can associate with each other, forming recombinant DNA DNA ligase joins DNA fragments together Animation: Restriction Enzymes Copyright © 2009 Pearson Education, Inc. Restriction enzyme recognition sequence 1 DNA Restriction enzyme cuts the DNA into fragments 2 Sticky end Restriction enzyme recognition sequence 1 DNA Restriction enzyme cuts the DNA into fragments 2 Sticky end Addition of a DNA fragment from another source 3 Restriction enzyme recognition sequence 1 DNA Restriction enzyme cuts the DNA into fragments 2 Sticky end Addition of a DNA fragment from another source Two (or more) fragments stick together by base-pairing 4 3 Restriction enzyme recognition sequence 1 DNA Restriction enzyme cuts the DNA into fragments 2 Sticky end Addition of a DNA fragment from another source 3 Two (or more) fragments stick together by base-pairing 4 DNA ligase pastes the strands 5 Recombinant DNA molecule 12.3 Cloned genes can be stored in genomic libraries A genomic library is a collection of all of the cloned DNA fragments from a target genome Genomic libraries can be constructed with different types of vectors – Plasmid library: genomic DNA is carried by plasmids – Phage library: genomic DNA is incorporated into bacteriophage DNA – Bacterial artificial chromosome (BAC) library: specialized plasmids can carry large DNA sequences Copyright © 2009 Pearson Education, Inc. Genome cut up with restriction enzyme Recombinant plasmid Recombinant phage DNA or Bacterial clone Plasmid library Phage clone Phage library GENETICALLY MODIFIED ORGANISMS Copyright © 2009 Pearson Education, Inc. 12.6 Recombinant cells and organisms can mass-produce gene products Cells and organisms containing cloned genes are used to manufacture large quantities of gene products Capabilities of the host cell are matched to the characteristics of the desired product – Prokaryotic host: E. coli – Can produce eukaryotic proteins that do not require posttranslational modification – Has many advantages in gene transfer, cell growth, and quantity of protein production – Can be engineered to secrete proteins Copyright © 2009 Pearson Education, Inc. 12.6 Recombinant cells and organisms can mass-produce gene products Capabilities of the host cell are matched to the characteristics of the desired product – Eukaryotic hosts – Yeast: S. cerevisiae – Can produce and secrete complex eukaryotic proteins – Mammalian cells in culture – Can attach sugars to form glycoproteins – “Pharm” animals – Will secrete gene product in milk Copyright © 2009 Pearson Education, Inc. 12.7 CONNECTION: DNA technology has changed the pharmaceutical industry and medicine Products of DNA technology – Therapeutic hormones – Insulin to treat diabetes – Human growth hormone to treat dwarfism – Diagnosis and treatment of disease – Testing for inherited diseases – Detecting infectious agents such as HIV Copyright © 2009 Pearson Education, Inc. 12.7 CONNECTION: DNA technology has changed the pharmaceutical industry and medicine Products of DNA technology – Vaccines – Stimulate an immune response by injecting – Protein from the surface of an infectious agent – A harmless version of the infectious agent – A harmless version of the smallpox virus containing genes from other infectious agents Copyright © 2009 Pearson Education, Inc. 12.7 CONNECTION: DNA technology has changed the pharmaceutical industry and medicine Advantages of recombinant DNA products – Identity to human protein – Purity – Quantity Copyright © 2009 Pearson Education, Inc. 12.8 CONNECTION: Genetically modified organisms are transforming agriculture Genetically modified (GM) organisms contain one or more genes introduced by artificial means Transgenic organisms contain at least one gene from another species GM plants – Resistance to herbicides – Resistance to pests – Improved nutritional profile GM animals – Improved qualities – Production of proteins or therapeutics Copyright © 2009 Pearson Education, Inc. Agrobacterium tumefaciens DNA containing gene for desired trait 1 Ti plasmid Insertion of gene into plasmid Restriction site Recombinant Ti plasmid Agrobacterium tumefaciens Plant cell DNA containing gene for desired trait 1 Ti plasmid Insertion of gene into plasmid 2 Recombinant Ti plasmid Introduction into plant cells DNA carrying new gene Restriction site Agrobacterium tumefaciens Plant cell DNA containing gene for desired trait 1 Ti plasmid Insertion of gene into plasmid 3 2 Recombinant Ti plasmid Introduction into plant cells Regeneration of plant DNA carrying new gene Restriction site Plant with new trait 12.9 Genetically modified organisms raise concerns about human and environmental health Scientists use safety measures to guard against production and release of new pathogens Concerns related to GM organisms – Can introduce allergens into the food supply – FDA requires evidence of safety before approval – Exporters must identify GM organisms in food shipments – May spread genes to closely related organisms – Hybrids with native plants may be prevented by modifying GM plants Regulatory agencies address the safe use of biotechnology Copyright © 2009 Pearson Education, Inc. 12.10 CONNECTION: Gene therapy may someday help treat a variety of diseases Gene therapy aims to treat a disease by supplying a functional allele One possible procedure – Clone the functional allele and insert it in a retroviral vector – Use the virus to deliver the gene to an affected cell type from the patient, such as a bone marrow cell – Viral DNA and the functional allele will insert into the patient’s chromosome – Return the cells to the patient for growth and division Copyright © 2009 Pearson Education, Inc. 12.10 CONNECTION: Gene therapy may someday help treat a variety of diseases SCID (severe combined immune deficiency) was the first disease treated by gene therapy – First trial in 1990 was inconclusive – Second trial in 2000 led to the development of leukemia in some patients due to the site of gene insertion Challenges – Safe delivery to the area of the body affected by the disease – Achieving a long-lasting therapeutic effect – Addressing ethical questions Copyright © 2009 Pearson Education, Inc. Cloned gene (normal allele) 1 Insert normal gene into virus Viral nucleic acid Retrovirus 2 Infect bone marrow cell with virus 3 Viral DNA inserts into chromosome Bone marrow cell from patient Bone marrow 4 Inject cells into patient DNA PROFILING Copyright © 2009 Pearson Education, Inc. 12.11 The analysis of genetic markers can produce a DNA profile DNA profiling is the analysis of DNA fragments to determine whether they come from a particular individual – Compares genetic markers from noncoding regions that show variation between individuals – Involves amplification (copying) of markers for analysis – Sizes of amplified fragments are compared Copyright © 2009 Pearson Education, Inc. Crime scene 1 DNA isolated 2 DNA of selected markers amplified 3 Amplified DNA compared Suspect 1 Suspect 2 12.12 The PCR method is used to amplify DNA sequences Polymerase chain reaction (PCR) is a method of amplifying a specific segment of a DNA molecule Relies upon a pair of primers – Short DNA molecules that bind to sequences at each end of the sequence to be copied – Used as a starting point for DNA replication Repeated cycle of steps for PCR – Sample is heated to separate DNA strands – Sample is cooled and primer binds to specific target sequence – Target sequence is copied with heat-stable DNA polymerase Copyright © 2009 Pearson Education, Inc. 12.12 The PCR method is used to amplify DNA sequences Advantages of PCR – Can amplify DNA from a small sample – Results are obtained rapidly – Reaction is highly sensitive, copying only the target sequence Copyright © 2009 Pearson Education, Inc. Cycle 1 yields 2 molecules Genomic DNA 3 1 3 5 3 Target sequence 5 5 5 3 Cycle 2 yields 4 molecules 5 5 2 Cool to allow 3 Heat to primers to form separate DNA strands hydrogen bonds with ends of target sequences 5 3 5 3 Primer 3 5 DNA polymerase adds nucleotides to the 3 end of each primer 5 3 New DNA Cycle 3 yields 8 molecules Cycle 1 yields 2 molecules Genomic DNA 3 3 5 5 3 Target sequence 5 3 3 5 5 3 2 Cool to allow 1 Heat to primers to form separate DNA strands hydrogen bonds with ends of target sequences 5 5 3 5 3 Primer 5 DNA polymerase adds nucleotides to the 3 end of each primer 5 3 New DNA Cycle 2 yields 4 molecules Cycle 3 yields 8 molecules 12.13 Gel electrophoresis sorts DNA molecules by size Gel electrophoresis separates DNA molecules based on size – DNA sample is placed at one end of a porous gel – Current is applied and DNA molecules move from the negative electrode toward the positive electrode – Shorter DNA fragments move through the gel pores more quickly and travel farther through the gel – DNA fragments appear as bands, visualized through staining or detecting radioactivity or fluorescence – Each band is a collection of DNA molecules of the same length Video: Biotechnology Lab Copyright © 2009 Pearson Education, Inc. Mixture of DNA fragments of different sizes Power source Longer (slower) molecules Gel Shorter (faster) molecules Completed gel 12.14 STR analysis is commonly used for DNA profiling Short tandem repeats (STRs) are genetic markers used in DNA profiling – STRs are short DNA sequences that are repeated many times in a row at the same location – The number of repeating units can differ between individuals – STR analysis compares the lengths of STR sequences at specific regions of the genome – Current standard for DNA profiling is to analyze 13 different STR sites Copyright © 2009 Pearson Education, Inc. STR site 1 STR site 2 Crime scene DNA Number of short tandem Number of short tandem repeats match repeats do not match Suspect’s DNA Crime scene DNA Suspect’s DNA 12.15 CONNECTION: DNA profiling has provided evidence in many forensic investigations Forensics – Evidence to show guilt or innocence Establishing family relationships – Paternity analysis Identification of human remains – After tragedies such as the September 11, 2001, attack on the World Trade Center Species identification – Evidence for sale of products from endangered species Copyright © 2009 Pearson Education, Inc. 12.16 RFLPs can be used to detect differences in DNA sequences Single nucleotide polymorphism (SNP) is a variation at one base pair within a coding or noncoding sequence Restriction fragment length polymorphism (RFLP) is a variation in the size of DNA fragments due to a SNP that alters a restriction site – RFLP analysis involves comparison of sizes of restriction fragments by gel electrophoresis Copyright © 2009 Pearson Education, Inc. Restriction enzymes added DNA sample 1 DNA sample 2 w Cut z x Cut Cut y y Longer fragments z x Shorter fragments w y y GENOMICS Copyright © 2009 Pearson Education, Inc. 12.17 Genomics is the scientific study of whole genomes Genomics is the study of an organism’s complete set of genes and their interactions – Initial studies focused on prokaryotic genomes – Many eukaryotic genomes have since been investigated Evolutionary relationships can be elucidated – Genomic studies showed a 96% similarity in DNA sequences between chimpanzees and humans – Functions of human disease-causing genes have been determined by comparisons to similar genes in yeast Copyright © 2009 Pearson Education, Inc. 12.18 CONNECTION: The Human Genome Project revealed that most of the human genome does not consist of genes Goals of the Human Genome Project (HGP) – To determine the nucleotide sequence all DNA in the human genome – To identify the location and sequence of every human gene Copyright © 2009 Pearson Education, Inc. 12.18 CONNECTION: The Human Genome Project revealed that most of the human genome does not consist of genes Results of the Human Genome Project – Humans have 21,000 genes in 3.2 billion nucleotide pairs – Only 1.5% of the DNA codes for proteins, tRNAs, or rRNAs – The remaining 88.5% of the DNA contains – Control regions such as promoters and enhancers – Unique noncoding DNA – Repetitive DNA – Found in centromeres and telomeres – Found dispersed throughout the genome, related to transposable elements that can move or be copied from one location to another Copyright © 2009 Pearson Education, Inc. Exons (regions of genes coding for protein or giving rise to rRNA or tRNA) (1.5%) Repetitive DNA that includes transposable elements and related sequences (44%) Introns and regulatory sequences (24%) Unique noncoding DNA (15%) Repetitive DNA unrelated to transposable elements (15%) 12.20 Proteomics is the scientific study of the full set of proteins encoded by a genome Proteomics – Studies the proteome, the complete set of proteins specified by a genome – Investigates protein functions and interactions The human proteome may contain 100,000 proteins Copyright © 2009 Pearson Education, Inc. 12.21 EVOLUTION CONNECTION: Genomes hold clues to the evolutionary divergence of humans and chimps Comparisons of human and chimp genomes – Differ by 1.2% in single-base substitutions – Differ by 2.7% in insertions and deletions of larger DNA sequences – Human genome shows greater incidence of duplications – Genes showing rapid evolution in humans – Genes for defense against malaria and tuberculosis – Gene regulating brain size – FOXP2 gene involved with speech and vocalization Copyright © 2009 Pearson Education, Inc. You should now be able to 1. Distinguish between terms in the following groups: restriction enzyme—DNA ligase; GM organism—transgenic organism; genomics— proteomics 2. Define the following terms: cDNA, gel electrophoresis, gene cloning, genomic library, “pharm” animal, plasmid, recombinant DNA, repetitive DNA, vector 3. Describe how genes are cloned Copyright © 2009 Pearson Education, Inc. You should now be able to 4. Describe how gene therapy has been attempted and identify challenges to the effectiveness of this treatment approach 5. Distinguish between the use of prokaryotic and eukaryotic cells in producing recombinant DNA products 6. Identify advantages to producing pharmaceuticals with recombinant DNA technology Copyright © 2009 Pearson Education, Inc. You should now be able to 8. Describe the basis for DNA profiling and explain how it is used to provide evidence in forensic investigations 9. Explain how PCR provides copies of a specific DNA sequence 10. Identify ethical concerns related to the use of recombinant DNA technology 11. Describe how comparative information from genome projects has led to a better understanding of human biology Copyright © 2009 Pearson Education, Inc.