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Bio102: Introduction to Cell Biology and Genetics Genetic Code and Mutation Key Terms: inborn error of metabolism metabolic pathway minimal media auxotroph Central Dogma One Gene-One Enzyme wildtype (wt) transcription translation genetic code Start and Stop Codons codon redundancy reading frame mRNA mutation mutagen missense mutation nonsense mutation frameshift mutation silent mutation carcinogen Ames test reversion Lecture Outline: Archibald Garrod describes “inborn errors of metabolism” blocks a metabolic pathway, causing accumulation of an intermediate in the pathway Beadle and Tatum experiment induced mutations in Neurospora crassa with x-rays found mutants that were arginine (an amino acid) auxotrophs, so they needed added arg to live some could live with ornithine or citrulline, precursors in the arginine metabolic pathway deduced that a gene corresponds to one enzyme, thus the One Gene-One Enzyme Hypothesis Central Dogma: information moves from DNA (gene) RNA Protein Genetic Code describes which three-nucleotide codon on the mRNA corresponds to which amino acid code is universal and redundant (so one amino acid may be encoded by >1 codon) always starts with AUG codon (=Met amino acid) each codon is then translated in-frame ends with either UAA, UGA or UAG (which do NOT correspond to an amino acid) Mutation is a change in the DNA. May effect the protein sequence. Missense mutations change one amino acid (e.g. UAC CAC) Nonsense mutations change an amino acid codon to a stop codon (e.g. UAC UAA) Insertions or deletions cause a change in the reading frame (e.g. UAC UA) Silent mutations make no change in the protein (e.g. UAC UAU) Ames test is used to find mutagenic chemicals. Measures mutation rate of a reversion that allows Salmonella bacteria to no longer by a histidine auxotroph.