CHAPTER 21 DNA Technology Genomics What is Genetic Engineering? Genetic engineering Moving genes from one organism to another Genes can be taken from one organism (plant, animal, virus, or bacteria) and transferred to another. Examples: Moving a human gene (e.g. the insulin gene) into bacteria Moving a bacterial gene (e.g. Bt toxin) into plants What are plasmids? Plasmids are small rings of DNA found in bacteria they are separate from the much larger bacterial chromosome. How is genetic engineering used? Medicine To develop drugs insulin, anticoagulants, human growth hormone, etc Use GE to obtain large amounts of rare proteins To make vaccines against viruses Agriculture Introduce pesticides or herbicideresistance into plants
What was the First Commercial Use of Genetic Engineering? Making human insulin Producing human insulin in bacteria. In 1982, the FDA approved genetically engineered insulin for use by diabetics. Most of the insulin that s used to treat diabetics is now obtained from GE bacteria that contain the human insulin gene Humulin is produced in 4-story tall fermentation vats Pig pancreases were once used as a source of insulin. Contamination was a problem And it was the pig (not human) hormone Now GE bacteria produce large quantities of pure human insulin What is Insulin? Engineering bacteria to make human insulin Insulin is a hormone that regulates blood sugar levels Made by the B cells of the pancreas Works together with glucagon to keep blood glucose levels constant insulin Isolate the gene for insulin and paste it into a plasmid Transfer the plasmid into bacteria Bacteria reproduce rapidly They become tiny insulin-producing factories Human insulin is isolated from the fermentation vat Using DNA technology to make vaccines Vaccines protect the body against disease-causing organisms (usually a virus) Some vaccines are purified proteins derived from a virus. Injected into a person Immune response Person is protected from infection by that virus How vaccines work Stimulate an immune response Protect the body against disease-causing organisms The body responds by creating Antibodies Memory cells that mount an immune response when the person is infected with the disease-causing organism.
GE medicines Insulin Human growth hormone (hgh) Clotting factor VIII Tissue plasminogen activator (t-pa) Hepatitis B vaccine What are antibiotics? Drugs that target infectious bacteria How do antibiotics kill bacteria without harming human cells? They bind to structures found only in bacterial cells Examples: Tetracyclin inactivates the bacterial ribosome, but not the human ribosome Penicillin disrupts synthesis of bacterial cell wall What are antibiotics? Antibiotics only kill bacteria and not every antibiotic is effective against every strain of bacteria. Colds and flu are caused by viruses Antibiotic resistance Bacteria can develop resistance to antibiotics. Especially when someone takes just part of their prescribed pills This allows mutant bacteria that are killed more slowly by the drug to survive and multiply. Genetically Engineered Crops Genetically engineered food Moving genes from one organism to another (a plant in this case) Example: Isolate the gene for Bt, a bacterial toxin that kills insect larvae (caterpillars), and move it into corn Bt Bt corn that makes its own pesticide
Genetically Engineered Crops Bt corn produces a toxin that kills corn borer caterpillars It makes its own pesticide Most common traits introduced The most common types of genetic changes in GE crops Resistance to insects Bt crops Contain the Bt gene for a bacterial toxin that kills certain insects a natural pesticide Resistance to weed killers (herbicides) found in over 80% of GE crops planted worldwide Genetic engineering for pest control Top 3 GE crops in the US Which of these potato plants is pestresistant? In 2008, 92% of the soybeans and 80% of the corn planted in the US had been genetically engineered Why genetic engineering is good for agriculture Introduce desirable traits Make crop easier to grow Resistant to herbicides Resistant to insects (Bt) Increase yield Improve nutritional content more protein, vitamins Tolerate stress Drought-tolerance and salt-tolerance Transgenic golden rice Golden rice contains genes from a bean, a fungus, wild rice, and a daffodil to increase its nutritional value
Golden rice Genetically modified to produce iron and betacarotene, a precursor of Vitamin A. Golden rice Developed in 2000 2010: nearing approval in several countries Took over 10 yrs to demonstrate that golden rice is safe for the environment and for consumption Same process for other GE crops Able to proceed more rapidly if variety has been bred traditionally Have you eaten a GE food? 50% of corn, 76% of soybeans grown in U.S. are GE crops. Currently, about 70% of processed foods in U.S. contain genetically engineered ingredients Look for high fructose corn syrup in soda, cereal, chips, mayo, etc Concerns about GE crops are they Frankenfoods? Is eating GM food dangerous? does adding genes introduce novel proteins that maybe potentially harmful when consumed? could introduced proteins be allergens? Each crop is tested for safety 3 government agencies monitor GE foods Genomics Genomics Genomics = study of an organism s entire genome or entire DNA sequence billion bases % of DNA shared Humans 3.2 99.5% Chimpanzee 2.8 98.5% Mouse 2.5 80% Chicken 1.0
So what s a genome? The Human Genome Completed in 2004 Contains 3.2 billion base pairs But only 25,000 genes a surprise About the same as other organisms More than one million single nucleotide changes (SNPs) These small genetic differences between people will usher in a new era of personalized medicine evolution human genome [4 min] http://www.youtube.com/watch?v=gngsl9frpqc&feature=related The human genome What is the next step in the HGP? Less than 2% of the genome codes for proteins The rest? Introns Regulatory sequences Repeated sequences and (controversially) "junk" DNA Functional genomics Understanding how the 25,000 genes function Understanding the function of intergenic regions 25% of DNA Comparative genomics Help understand how species have evolved Comparing human genomes may help identify base sequences that cause illness Increase our understanding of gene regulation Everyone s DNA is unique The DNA in our genomes can be used like a fingerprint But we all share 99.5% of our DNA How does this happen? Here s an example of a SNP Normal (HbA) Mutant (HbS) A change in a single nucleotide in the gene for the β subunit of hemoglobin (CTC to CAC) What are SNPs? http://www.youtube.com/watch?v=5rajepxu0oq&feature=related
What can we learn from SNPs? Analyze the DNA of people with and without a particular disease Tally the SNPs that are found in people with disease Identify SNPs that predispose individuals to diabetes, bipolar disorder, coronary artery disease and other diseases OMG guess what my genes say! Right now we understand very little of the meaning of those 3 billion bases About 20 potentially preventable health problems can be detected with gene testing e.g. BRCAI gene breast cancer Coming soon inexpensive, widely available whole-genome sequencing Personalized medicine Personalized medicine Drug therapy is chosen for each patient based on their particular genetic profile DNA Fingerprinting and Forensic Science DNA technology has revolutionized the field of forensics. Forensics is the scientific analysis of evidence from crime scenes. DNA fingerprinting can be used to determine whether or not two samples of DNA are from a particular individual. Used in murder, rape and paternity cases DNA fingerprinting 1. Collect DNA samples 2. Amplify (copy) regions of the DNA lots of DNA fragments 3. Compare the size of the DNA fragments by gel electrophoresis
Genomics is used to understand how organisms are related Grebes (left) and flamingoes are close relatives. But surprisingly, neither of the aquatic species are descended from--or even closely related to--other water birds. A genetic study changed the bird family tree UC Berkeley researchers sequenced regions of 14 chromosomes of 169 bird species Compared the DNA sequence Discovered that much of bird classification (based on appearance) is wrong R. Bowie, Science 2008 Pop quiz What are SNPs? Or single nucleotide polymorphisms A change in a single base in the DNA SNPs make everyone s DNA unique All SNPs cause mutations in genes Quick quiz The total amount of DNA in an organism, including all of its genes and other DNA, is called its SNPs Karyotype Genome Genetics Another question The pattern of bars in a DNA fingerprint shows The order of bases in a gene The presence of various-sized fragments of DNA The order of genes along the chromosome The exact location of a specific gene And another Why do DNA fragments move through a gel during electrophoresis? The electric charge of its phosphate groups Its nucleotide sequence The hydrogen bonds between base pairs The double helix shape A tricky question Why do humans have a smaller number of genes than expected? We only need 25,000 genes to function The exons used to make a specific mrna can be rearranged to form different RNAs The # of genes will increase as scientists find out what the junk DNA does We don t really know why