Essay

* analyse information from secondary sources to outline the evidence that led to Beadle and Tatum’s ‘one gene – one protein’ hypothesis and to explain why this was altered to the ‘one gene – one polypeptide’ hypothesis Beadle & Tatum (1941) conducted research to determine if & how genes control biochemical reactants. * They hypothesized that if there really was a one-to-one relationship between genes and specific enzymes, it should be possible to create genetic mutants that are unable to carry out specific enzymatic reactions. They: * used bread mould to investigate nutritional mutations (because bread mould was easy to maintain & induce mutation) * using X-rays, they produced mould that was unable to produce a specific amino acid (a mutant mould). The mould was unable grow unless the amino acid was added. * Beadle & Tatum hypothesised that this mutant mould had lost the ability to make the enzyme to create the amino acid (since the X-rays had mutated the gene). * They then hypothesised that for each gene, there was one enzyme (protein). * This was later changed to ‘one gene – one polypeptide.’ This was because the enzymes they studied consisted of one polypeptide, BUT many enzymes consist of chains of polypeptides. MODIFIED because: many proteins are comprised of more than one polypeptide that may be same/ different. Beadle & Tatum showed that genes controlled biochemical processes. * Beadle and Tatum (1930’s-40’s) set out to provide experimental proof of the connection between genes and enzymes. * They hypothesized that if there really was a one-to-one relationship between genes and specific enzymes, it should be possible to create genetic mutants that are unable to carry out specific enzymatic reactions. * To test this theory, they exposed spores of Neurospora crassa (a bread mould) to X-rays or UV radiation. (because bread mould was easy to maintain & induce mutation) * The mutant molds had a variety of special nutritional needs. * They could not live without the addition of particular vitamins or amino acids to their food. * As they had predicted, they were able to create single gene mutations that incapacitated specific enzymes, so that the molds with these mutations required an external supply of the substance that the enzyme normally produced, and the substance that the enzyme normally used, piled up in the cell. * These results led them to the one gene/one enzyme hypothesis : that each gene is responsible for directing the building of a single, specific enzyme. * It is more accurate to say: one gene – one polypeptide. This is because: * We now know that not all genes code for enzymes. * The enzymes that they studied consisted of one polypeptide but many enzymes consist of chains of polypeptides. E.g. Haemoglobin has 4 polypeptide chains of 2 different types and each of the chain types is controlled by a different gene. * This was later changed to ‘one gene – one polypeptide.’ This was because the enzymes they studied consisted of one polypeptide, BUT many enzymes consist of chains of polypeptides. MODIFIED because: many proteins are comprised of more than one polypeptide that may be same/ different.