BSC2010 BIOLOGICAL SCIENCE 1 SPRING 2012 STUDY GUIDE 15 The Central Dogma and Genetic Code Vocabulary Arginine Amino acid Beadle and Tatum Exposed bread mold to x rays o Created genetic mutants that were unable to survive on minimum medium as a result of the inability to synthesize certain molecules o Using genetic crosses they identified three classes of arginine deficient mutants each lacking a different enzyme necessary for synthesizing arginine o They developed the one gene one enzyme hypothesis which states that each gene dictates production of a specific enzyme Citrulline Codons Amino acid Arginine is first oxidized into N hydroxyl arginine which is then further oxidized to citrulline concomitant with release of nitric oxide The code defines how sequences of three nucleotides called codons specify which amino acid will be added next during protein synthesis The mRNA is read from the 5 to the 3 end and every three nucleotides codes for one amino acid Complete medium The three nucleotides that code for an amino acid is called a codon Contains nutrients vitamins an energy and carbon source and premade organic compounds such as amino acids and nucleotides Cells that grow in complete medium but not metabolic medium are metabolic mutants Garrod Inborn Errors of Metabolism metabolic pathways Metabolic mutant Minimum medium Thought symptoms of inherited diseases reflected the inability to synthesize enzymes in metabolic pathways He referred to those defects as inborn errors in metabolism Archibald Garrod Symptoms of inherited diseases reflected the inability to synthesize enzymes in Cells that grow in complete medium but not minimum medium Minimal media are those that contain the minimum nutrients possible for colony growth generally without the presence of amino acids and are often used by microbiologists and geneticists to grow wild type microorganisms mRNA Molecule of RNA that encodes a chemical blueprint for a protein product Neurospora Species is mold Ornithine Redundancy of the genetic code Several codons code for the same amino acid Replication Stop codon The Genetic Code Signal for the end of the protein and terminate protein synthesis UAA UAG UGA Codons are shown as they occur in mRNA from 5 to 3 Amino acids are indicated by their 2 letter abbreviation The genetic code is the set of rules by which information encoded in genetic material DNA or mRNA sequences is translated into proteins amino acid sequences by living cells Produces a strand of mRNA complementary to one of the DNA strands the Transcription template strand Translation Ribosomes read nucleotide sequence in the mRNA and use the information to synthesize a polypeptide with a specific sequence of amino acids tRNA Wild type An adaptor molecule composed of RNA Unmutated cells normal Principles and Concepts dogma Understand the steps and pathway of gene expression as summarized in the central o The DNA inherited by an organism leads to specific traits by dictating the synthesis of specific proteins o Gene expression the process by which DNA directs protein synthesis includes two stages Transcription and translation Be familiar with the experiments done with metabolic mutants in Neursopora to determine the relationship between genes and proteins Know how the experiments were designed performed and interpreted Understand the specific and general conclusions obtained from these experiments o 1 Neursopora growing on food in a test tube o 2 Treat with x rays to mutate genes o 3 Grow on complete medium so all cells can grow even metabolic mutants o 4 transferred to two test tubes Complete medium and minimal medium o Cells that grow in complete medium but not minimal medium are metabolic mutants o 5 From the complete medium deficiency is synthesize arginine Prepare more replicate cultures to determine what the metabolic o 6 Find growth in a certain test tube means that the cells are unable to o Find later that enzyme A goes with gene A enzyme B goes with gene B and enzyme C goes with gene C o Also learned that some proteins aren t enzymes and many proteins are composed of several polypeptide subunits so now this is called One gene one polypeptide hypothesis Understand the original one gene one enzyme hypothesis and why it has been updated to the one gene one polypeptide hypothesis o Enzyme A goes with gene A enzyme B goes with gene B and enzyme C goes with gene C o Also learned that some proteins aren t enzymes and many proteins are composed of several polypeptide subunits so now this is called One gene one polypeptide hypothesis Understand the flow of genetic information during transcription and translation how the sequence of the template strand of DNA is related to the mRNA sequence and how mRNA sequence is related to amino acid sequence in the polypeptide product of translation o Transcription o Translation o mRNA product Produces a strand of mRNA complementary to one of the DNA strands the template strand Ribosomes read nucleotide sequence in the mRNA and use the information to synthesize a polypeptide with a specific sequence of amino acids Molecule of RNA that encodes a chemical blueprint for a protein Know what codons are and how to read and use a genetic code table Know what the redundancy of the genetic codes means and know that 61 of the 64 possible three letter codons code for amino acids while the three remaining are stop codons Know what it means to say that the genetic code is universal o Genetic code is universal with a few exceptions Tobacco plant expresses a firefly gene A pig expresses a jellyfish gene Bacteria expresses human insulin Rice that make vitamin A
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