Blueprint of Life Topic 16: Beadle and Tatum

1. Blueprint of LifeTopic 16: Beadle and Tatum Biology in Focus, HSC Course Glenda Childrawi, Margaret Robson and Stephanie Hollis

2. DOT POINT(s) • 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.

3. Introduction The phenotype of an organism is its total appearance determined during development by an interaction between its genetic make-up (genotype) and the environment. themetapicture.com

4. Introduction A genome is all of the genetic material (DNA) within a cell and is specific to each organism. Genomes influence nearly all the traits or phenotypes, such as eye colour, height and susceptibility to disease, and most variations occur due to differing genomes. www.rsc.org

5. Introduction The phenotypic appearance is therefore directly affected by gene expression. The extent of phenotypic differences depends on how different the DNA sequences are in individuals, but may also be influenced by the environment. To what extent differences in genotype cause differing phenotypes has always been of interest to people. ravenousaddict.deviantart.com

6. Introduction The proposal that a gene is responsible for the production of a specific protein was first put forward by Archibald Garrod in 1909. This idea, together with work on the inheritance of eye colour in Drosophila, led biologists to investigate the importance of genes in enzyme production. www.dec.ufcg.edu.br

7. Beadle and Tatum George Beadle and Edward Tatum (1941) worked on mutants of the fungus Neurosporacrassa (a mould), leading to their groundbreakingdiscovery that genes provide the instructions for making proteins. sandwalk.blogspot.com

8. Beadle and Tatum They put forward the hypothesis that one gene controls the production of one enzyme. This was based on observations made in Beadle’s earlier experiments on fruit flies—he found that if fruit flies with normal eye colour were exposed to X-rays, their offspring would show a change in eye colour. He hypothesised that this occurred as a result of a defective enzyme for the eye pigment. news.sciencemag.org

9. Beadle and Tatum Since evidence was needed to support this hypothesis, Beadle and Tatum designed and carried out an experiment to attempt to mutate genes of the mould Neurosporacrassa, the enzyme functioning of which they could test fairly simply. www.dnaftb.org

10. Beadle and Tatum Experimental evidence led them to propose a hypothesis that genes affect enzyme production—the details of this were later modified as the understanding of the relationship between genes and proteins advanced. www.readcube.com

11. Beadle and Tatum’s Experiment It is important to remember that at the time that Beadle and Tatum began their research, biologists were still not sure of the chemical nature of the heredity material—there was still ongoing debate as to whether it would prove to be protein or DNA. This is why their discovery was such a major breakthrough. pinterest.com

12. Activity Visit website and do activity together (10-15min): http://www.dnalc.org/resources/nobel/beadle_tatum.html pinterest.com

13. Beadle and Tatum’s Experiment Beadle and Tatum’s ‘one gene—one enzyme’ hypothesis changed to the ‘one gene—one protein’ hypothesis, once it was demonstrated that there are other proteins besides enzymes that are encoded by genes. sandwalk.blogspot.com

14. Beadle and Tatum’s Experiment After the discovery by biologists that one gene is not necessarily responsible for the structure of an entire protein, but for each polypeptide chain making up that protein, the current one gene—one polypeptide hypothesis was adopted. This is the currently accepted theory and has stood up to rigorous testing, holding true for all predictions so far. users.rcn.com

15. Beadle and Tatum’s Experiment George Beadle and Edward Tatum’s discovery won them the Nobel Prize for Physiology or Medicine in 1958. www.readcube.com -

16. Activity/Homework -Students to visit site and go through experiment again on their own. http://www.dnalc.org/resources/nobel/beadle_tatum.html a