Gene Expression and GMO Chapter Notes PDF

Chapter 9 Gene Expression and GMO The Inheritance of Traits • Chromosomes are analogous to pages in the instruction manual for building a human • Genes are analogous to words in a page of the instruction manual build strong heart muscle Genes expressed in muscle cell build grow long dark blood...

Chapter 9 Gene Expression and GMO The Inheritance of Traits • Chromosomes are analogous to pages in the instruction manual for building a human • Genes are analogous to words in a page of the instruction manual build strong heart muscle Genes expressed in muscle cell build grow long dark blood brown strong hair for eyes heart small red muscle build dark brown eyes Genes expressed in eye cell Figure 6.3 From Gene to Protein • Gene Expression: convert information in a gene to a functional product - The most fundamental level at which the genotype gives rise to the phenotype - The product are mostly proteins • Protein synthesis: use instructions carried on a gene to create proteins From Gene to Protein • Several steps are involved and require both DNA and RNA (a) DNA (b) RNA RNA nucleotide DNA nucleotide Uracil (U) Thymine (T) Phosphate group Phosphate group Deoxyribose Ribose Figure 8.1 Similarity and Difference in the Structure of DNA and RNA # of strand(s) Sugar in the nucleotide Nitrogenous base in the nucleotide Phosphate group in the nucleotide DNA Double Deoxy-ribose RNA Single ribose Adenine (A) Thymine (T) Guanine (G) Cytosine (C) Yes Adenine (A) Uracil (U) Guanine (G) Cytosine (C) Yes From Gene to Protein • The flow of genetic information in a cell is DNA ® RNA ® Protein Polymer of nucleotides (two complementary strands) DNA Transcription (DNA à RNA) Polymer of nucleotides (single strand) RNA Translation (RNA à Protein) Protein ala ser val his Polymer of amino acids Figure 8.2 Transcription • Transcription: the copying of DNA into messenger RNA (mRNA) in gene expression - Occur in the nucleus - RNA polymerase: an enzyme that produces RNA - Match RNA nucleotides with complementary DNA nucleotides on the template strand Promoter RNA nucleotides DNA Promoters have distinct nucleotide sequences that RNA polymerase recognizes. RNA polymerase mRNA video DNA Figure 8.3 Non-Template (Sense) Lecture Activity: Decode the mystery in our body! • If a fragment of the template DNA strand is ATCCACCGG, what would be the sequence the mRNA made from it? • If an mRNA is AUCCACCGG, what would be the sequence on the template DNA strand? Translation • Translation: mRNA is decoded by the ribosome to produce an amino acid chain that later fold into an active protein - Occur in the cytoplasm (outside the nucleus) - Require energy - Require helper – Transfer RNA (tRNA) The Structure of Ribosome • The ribosome is made of proteins and ribosomal RNA (rRNA) • It is comprises a small and a large subunit • The Nobel Prize in Chemistry for 2009 Large subunit mRNA Small subunit Figure 8.4 The Structure of tRNA • Cloverleaf structure • Anticodon: a triplet sequence against the three bases of the codon on the mRNA • Acceptor arm: bind amino acids that match the anticodons Amino acid Binding site for amino acid Region of internal complementarity tRNA Anticodon mRNA Codon Figure 8.5 The Process of Translation 1 Amino acids and tRNAs float freely in the cytoplasm. 2 Enzymes facilitate the binding of a specific tRNA to its appropriate amino acid. Amino acid tRNA Figure 8.7 3 A tRNA will dock if the complementary RNA codon is present on the ribosome. val ser ala video 4 The amino acids join together to form a polypeptide. U AG Amino acid chain (polypeptide) ala phe G CG arg ile UCC Stop codon AAA UAU GCC UUU AUA Ribosome Figure 8.7 Amino acid chain (polypeptide) ala phe G CG arg ile UCC Stop codon AAA UAU GCCUUUAUA 5 The ribosome moves on to the next codon to receive the next tRNA. Ribosome 6 When the ribosome reaches the stop codon, no tRNA can basepair with the codon on the mRNA. RNA and the newly synthesized protein are released. Figure 8.7 Codons in mRNA and Amino Acids AUG – START Lecture Activity: Decode the mystery in our body! • If a fragment of mRNA is AUCCACCGG, what would be the amino acid chain that it codes for? _____ - _____ - _____ • If the anticodon on a tRNA is UCU, which amino acid does it carry? Gene Mutation and Protein Synthesis • Types of mutation: 1. Base substitution: CTA à CCA 2. Insertion: CTA à CTT A.. Frame shift 3. Delete: CTACCG à CAC CG. • Possible outcomes of mutation: 1. No change in protein: AAT à AAC 2. Non-functional protein 3. Different protein Substitution Mutation (b) Mutated DNA sequence (a) Normal DNA sequence Substitution mutation DNA DNA mRNA mRNA Protein met asp ala phe Functional protein Protein met gly ala phe Nonfunctional protein Figure 8.8 A base substitution (CTCàCAC) in the hemoglobin gene – Sickle cell disease – Can’t carry enough oxygen molecules Frame-shift Mutation DNA mRNA Amino acid sequence (b) Insertion of one base pair, resulting in a frameshift mutation Figure 8.9b The amino acid sequence is different from the original.In this case, a stop codon causes the formation of an incomplete protein. Genetically Modified Crops • Traditional plant breeding: selection and hybridization for particular genetic traits - Fairly Effective over the years - Negative aspects: - Take time - Environmental factors cannot always be controlled Figure 8.13 Genetically Modified Crops • Plant biotechnology: a set of techniques to adapt plants for specific needs - Transfer genetic information from one plant to the genome of another – Transgenic plant - Positive aspects: - More precise - Well-controlled environments Figure 8.16 Methods of Plant Improvement I. Traditional plant breeding Traditional donor DNA is a strand of genes, much like a strand of pearls. Traditional plant breeding combines many genes at once. Commercial variety New variety (many genes are transferred) = X (crosses) Desired Gene Desired gene II. Plant biotechnology Using plant biotechnology, a single gene may be added to the strand. Desired gene Commercial variety New variety (only desired gene is transferred) = (transfers) Desired gene 24 Techniques Being Used to Create GM Crops • Agrobacterium – transfer DNA between itself and plants Agrobacterium contains a small circular piece of DNA – Ti (Tumorinducing) plasmid Techniques Being Used to Create GM Crops • Gene gun – inject cells with DNA bounded to heavy metal particles, e.g. gold powder What Countries Have Adopted GM Crops? 1980s: First stably GM plant 1995: First commercialized GM plant Up to date: Worldwide: >1 billion acres US: > 50 trillion GM plants Figure 1.4 Plant Biotechnology and Genetics What Crop Species Have Been Engineered Using Plant Biotechnology? In US: More than 50% corn and cotton, and 75% soybean are GM plants Sources: ISAAA, Canola Council of Canada, CropLife Canada, USDA, CSIRO, ArgenBio. Figure 1.1 Plant Biotechnology and Genetics Case Study 1: “Round-up Ready” Crop • Roundup: a systemic, broadspectrum herbicide • #1 selling herbicide worldwide since at least 1980 • Active ingredient: glyphosate Case Study 1: “Round-up Ready” Crop • “Roundup Ready” Crop: crop plants that are resistant to the Roundup herbicide - 1996: Roundup Ready soybean - 1998: Roundup Ready corn - Current Roundup Ready crops: canola, sugar beet, cotton (wheat and alfalfa are under development) Case Study 2: “Bt” Crop • Bacillus thuringiensis (Bt): a soil-dwelling bacterium that produces a toxin to kill the pests fed on crops • The Bt toxin may be extracted and used as a pesticide Case Study 2: “Bt” Crop • Bt crop: crop plants producing the Bt toxin - 1995: Bt potato - 1996: Bt cotton, Bt maize Agencies in US Regulation of GMO • USDA: U. S. Department of Agriculture - Gene flow, agronomic effects • EPA: Environmental Protection Agency - Gene flow, environmental toxicity when plants harbor transgenes for pest control • FDA: Food and Drug Administration - Human toxicity, allergy effect Genetically Modified Humans • Human Genome Project – international effort to map the sequence of human genome Sequence from Lab 1 Sequence from Lab 2 Compiled sequence Sequence from Lab 3 Sequence from Lab 4 Figure 8.21 Genetically Modified Humans • Gene therapy – replacement of defective genes with functional genes - Germ line gene therapy – embryo supplied with a functional version of the defective gene - Somatic cell gene therapy – fix or replace the defective protein only in specific cells - Not permanent (Severe Combined Immuno-Deficiency) (a) Gene therapy for SCID patients Virus Normal allele Immune system cell 1 Remove immune system cells from patient. 2 Infect the cells with a virus carrying the normal allele. 3 Return cells carrying the normal allele. Figure 8.22a Genetically Modified Humans • Stem cells – undifferentiated cells, capable of growing in to many different kinds of cells and tissues - Two types: mature vs. embryonic stem cell - Potency: the potential to differentiate into different cell types Totipotent > Pluripotent > Multipotent > Unipotent Embryonic Stem Cell Mature Stem Cell Multipotent or Most common type of mature stem cell – Bone marrow stem cell; to treat cancer patients with leukemia and lymphoma The primary sources of embryonic stem cell for research are created by the in vitro fertilization (IVF) process; to grow specific tissues for transplantation (skin, heart, kidney, joint); ethical dilemma Genetically Modified Humans • Cloning – making genetically identical copies of an individual 2012 Nobel Prize in Physiology or Medicine – discovering that mature body cells can be reprogrammed into stem cells John Gurdon Shinya Yamanaka Creation of Dolly (July 5, 1996 ~ Feb. 14, 2003) Mammary cell 2 1 Isolate mammary cell from one sheep and egg cell from another. Remove the nucleus from the egg cell. Fuse the egg cell and mammary cell. Fused cell 3 The egg cell now contains the nucleus from the mammary cell. Embryo 4 Egg cell 5 Dolly the cloned lamb 6 Figure 8.23 Grow the embryo in a culture. Implant the early embryo into the uterus of a third sheep (black face) that has been hormonally treated to simulate pregnancy. Surrogate mother gives birth to a lamb (Dolly) that is genetically identical to the mammary cell donor.