Bio102: Introduction to Cell Biology and Genetics
Genetic Code and Mutation
Key Terms:
inborn error of One Gene-One Start and Stop mutation mutagen
metabolism Enzyme Codons
metabolic pathway wildtype (wt) codon missense mutation carcinogen
minimal media transcription redundancy nonsense mutation Ames test
auxotroph translation reading frame frameshift mutation reversion
Central Dogma genetic code mRNA silent mutation
Key Figures: Figures 17.2, 17.3, 17.4, 17.5, 17.23
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.