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Chapter 17
From Gene to Protein
Rob Swatski
Associate Professor of Biology
HACC – York Campus
Overview: The Flow of Genetic Information
DNA information = specific sequences of nucleotides DNA protein synthesis
Proteins: link genotype & phenotype Gene expression: DNA directs protein synthesis - 2 stages: transcription & translation
How was the fundamental relationship between genes & proteins discovered? - examine evidence from studies of metabolic defects
1909: British physician Archibald Garrod 1st suggested that genes dictate phenotypes with enzymes
- symptoms of inherited disease reflects inability to synthesize a certain enzyme - required understanding that cells synthesize & degrade molecules using metabolic pathways
Neurospora bread mold
Nutritional Mutants in Bread Mold
George Beadle & Edward Tatum exposed Neurospora to x-rays - created mutants that could not survive on minimal medium (cannot synthesize certain molecules) Identified 3 classes of arginine-deficient mutants - each lacked a different enzyme needed to make arginine Developed the “one gene – one enzyme hypothesis” - each gene directs the synthesis of a specific enzyme
EXPERIMENT
Growth:
Wild-type cells growing and dividing
No growth:
Mutant cells cannot grow and divide
Minimal medium
RESULTS
Classes of Neurospora crassa
Wild type Minimal medium (MM) (control) MM ornithine
Growth
Class I mutants
No growth
Class II mutants
Class III mutants
Condition
MM citrulline
MM arginine (control) Summary of results
Can grow with or without any supplements
Can grow on ornithine, citrulline, or arginine
Can grow only on citrulline or arginine
Require arginine to grow
CONCLUSION
Gene (codes for enzyme)
Class I mutants (mutation in gene A) Precursor
Enzyme A
Wild type Precursor
Class II mutants (mutation in gene B) Precursor
Enzyme A
Class III mutants (mutation in gene C) Precursor
Enzyme A
Gene A...