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Objectives
- Describe the design of the Beadle and Tatum experiment and how it provides evidence for the one gene, one polypeptide hypothesis
- Explain the central dogma
Key points
How are traits linked to inheritance?
- Beadle and Tatum used Neurospora to study the relationship between DNA and traits
- they mutagenized spores and isolated colonies that couldn’t grow on minimal media (known as auxotrophic mutants)
- they transferred spores of auxotrophic mutants to arginine media and noted those that recovered, reasoning that they must be mutants in one of the steps of arginine biosynthesis
- they subcultured their mutants on media supplemented with an intermediate in the pathway and found classes of mutations that recovered:
- some recovered on media with ornithine, the first intermediate in the pathway
- some recovered on citruline, the second intermediate
- some only recovered on arginine, the product of the pathway
- their interpretation of their results was that each class of mutation corresponded to the loss of a specific enzyme in the pathway, and that by supplying the product of that enzyme they could rescue the growth on minimal media
- they concluded that one gene dictates the production of one enzyme, now revised to state that one gene dictates one polypeptide
Central dogma
- the idea that DNA encodes RNA, which in turn encodes proteins
- DNA is an information storing molecule, and the information it stores often is the instruction set for building a specific protein via messenger RNA (mRNA)
- DNA also encodes other forms of RNA that are catalytic or structural (ribosomal and transfer RNA)