Chapter 12 - 204-325 1 Summary of the Last Lecture DNA...

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Unformatted text preview: 204-325 1 Summary of the Last Lecture DNA replicates semiconservatively and bidriectionally. DNA polymerases catalyze the synthesis of DNA only in 5' to 3' direction by extending existing 3' end of a DNA or RNA molecule. DNA double helix replicates semidiscontinuously. Lagging strand of a replication fork is first replicated in many Okazaki fragments, which are ligated together. Eukaryotic chromosomes contain multiple replication origins. Prokaryotic chromosomes have only one. At the end of linear chromosome, telomerase extends telomere in some cells to compensate for the shortening. In DNA recombination, 2 DNA helices align. A cut is made. Broken ends invade the other helix. Branch migration and resolution determine the outcome. 2 The Central Dogma Genotype Phenotype 3 Today's Topics 1. One Gene - One Enzyme 2. Genetically Based Enzyme Deficiencies in Human Diseases 3. Genetic Control of Protein Structure and Function 4 Topic 1 One Gene One Enzyme 5 Neurospora crassa: Orange Bread Mold 6 Life Cycle of Neurospora Crassa 7 Identify Auxotrophic Mutations in Neurospora 8 Methionine Biosynthetic Pathway in Neurospora 9 One Gene One Enzyme Each gene controls the synthesis or activity of a single enzyme. ----- Beadle and Tatum 10 Animation 1: Beadle and Tatum Experiment 11 Topic 2 Genetically Based Enzyme Deficiencies in Human Diseases 12 Phenylketonuria, Alkaptonuria and Albinism X Phenylketonuria X Albinism X Mental Retardation Slow Growth Early Death Black urine X Alkaptonuria Arthritis 13 Albinism: No Melanin 14 Tay Sachs Disease: A Lysosomal Storage Disease X Paralysis Blind, Deaf Death by 3-4 yr 15 Tay Sachs Disease: Loss Brain Functions, Death ~3 yr old 16 Lesch-Nyhan Disease: Purine Metabolism Defect Hypoxanthine-guanine phosphoribosyltransferase (HPRT) 17 x Excess uric acid Mental retardation Self-mutilation Death before 20 yr Lesch-Nyhan Disease 18 Topic 3 Genetic Control of Protein Structure and Function 19 Sickle Shaped Red Blood Cell 20 The Hemoglobin Molecule 21 Normal and Sickled Hemoglobin -Polypeptides Nonenzymatic Protein Mutation 22 Electrophoresis 23 Electrophoresis of Hemoglobin Variants + Sample Loaded 24 Change of One Amino Acid Causes Sickle-Cell Anemia 25 Pleiotropic Effect of Sickle Cell Anemia Pleiotropy: One mutation has multiple phenotypes 26 Heterozygotes and Homozygotes 27 Human Hemoglobin Polypeptide Variants 28 Human Hemoglobin Polypeptide Variants 29 Animation 2: Sickle Cell Anemia 30 Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) 31 Online Mendelian Inheritance in Man http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=OMIM 32 Mendelian Inheritance in Human 2005: 15877 2006: 16603 2007: 17480 33 Examples of Human Genetic Disease Alkaptonuria Penylketonuria Albinism Tay-Sachs Disease Lesch-Nyhan Syndrome Sickle-Cell Anemia Cystic Fibrosis 26 34 Examples of Human Genetic Diseases with Enzyme Deficiency 35 Amniocentesis for Prenatal Diagnosis of Genetic Defects > 12 weeks 36 Chorionic Villus Sampling for Prenatal Diagnosis 8-12 weeks 37 Summary Protein sequence is encoded by its gene. Gene products (enzymes) can work in specific order in a biochemical pathway. Single gene mutations account for many, but not all, genetic diseases in human. Genes also make proteins that are not enzymes. Mutations of these genes can also cause inheritable disorders. Genetic counseling involves genotype analysis, explaining consequence and presenting options. 38 ...
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