From Gene to Protein: Chpt. 17

1. From Gene to Protein: Chpt. 17

2. How does the DNA lead to specific traits??? ArchibaldGarrod (1909)hypothesized: “proteins are the link between genotype & phenotype”

3. 1909 - Archibald Garrod • Suggested genes controlenzymes, & enzymes catalyze chemical processes in cells. Inherited Diseases are “inborn errors of metabolism” where a person can’tmakeanenzyme.”

4. Example • Alkaptonuria(Al ka toe nuria)- where urine turnsblackafter exposure to air b/c of chemical alkapton (Al kae ton). • these individuals must lack an enzyme to metabolize (break down)alkapton (the chemical).

5. enzyme enzyme enzyme enzyme

6. GeorgeBeadleAmerican(1930) *“ mutations in eye color (Drosophila) are a result of blocks in pigment production” *“no enzyme is made - therefore pathway to produce color pigment is not complete… white eyes”

8. G.Beadle & Edward Tatum Beadle and Tatum set out to provide experimental proof of the connection between genes and enzymes.

9. G.Beadle & Edward Tatum Cal Tech. Rockefeller Inst. NY, NY Nobel Prize in Physiology or Medicine 1958 "for their discovery that genes act by regulating definite chemical events"

10. G.Beadle & Edward Tatum test organism = Neurospora Neurospora (pink bread mold)

11. G.Beadle & Edward Tatum mutant molds (not wild type) had a variety of special nutritional needs. Unlike their wild type counterparts, they could not live without the addition of particular vitamins or amino acids to their food.

12. G.Beadle & Edward Tatum *“ various mutations must be abnormal variations of genes”

13. One Gene, One Enzyme Hypothesis -Beadle & Tatum this is the normal metabolic pathway wild type mold survived in minimalmediumagar. The wild type mold can produce all of the enzymes it needs to produce the necessary amino acids to live.

14. One Gene, One Enzyme Hypothesis -Beadle & Tatum Mutantsdid notsurvive in minimal medium agar. The mutants must not produce all of the enzymes needed The enzymes would synthesize particular amino acids. But they could survive in complete agar… supplemented with all 20 amino acids.

15. One Gene, One Enzyme Hypothesis -Beadle & Tatum The Experiment

16. One Gene, One Enzyme Hypothesis -Beadle & Tatum Tried to identify where the mutants’ metabolic defects (mutations) were

17. One Gene, One Enzyme Hypothesis -Beadle & Tatum All strains were grown on complete media. This contained all a.a. & vitamins made by the wild type, they all thrived… By the way, this mold MUST make Arginine in order to grow.

18. One Gene, One Enzyme Hypothesis -Beadle & Tatum Took mutants out of the complete media They did not all grow when put on “minimal media” They figured that mutants were unable to produce compounds essential for growth… perhaps their genes did not code for an enzyme… this ultimately did not let the organism produce arginine??

19. One Gene, One Enzyme Hypothesis -Beadle & Tatum Put each mutant type in different vials containing minimal + one amino acid. (in this pix., the a.a. is ornathine)

20. Because Class I grew on minimal medium supplemented with ornithine, citrulline, or argine, it had to be missing enzyme A. This would be required to form all three compounds

21. One Gene, One Enzyme Hypothesis -Beadle & Tatum Class II could not produce citruline, and that is needed for the rest of the pathway to occur... Ornathine “piled up”

22. One Gene, One Enzyme Hypothesis -Beadle & Tatum The media that allowed growth, would show where the metabolic defect (mutation) occurred there was always a “pile up” of the amino acid before

23. One Gene, One Enzyme Hypothesis -Beadle & Tatum If we inactivate one gene, that would code for an enzyme to carry out X -> Y conversion, no product X or Y is produced. If product Y is needed to ultimately produce arginine, no growth will occur

24. One Gene, One Enzyme Hypothesis -Beadle & Tatum The supplement that allowed growth, would show where the metabolic defect (mutation) occurred

25. One Gene, One Enzyme Hypothesis -Beadle & Tatum

26. One Gene, One Enzyme Hypothesis -Beadle & Tatum ex. this mutant grew (was able to complete the pathway) in the vial supplemented with Citrulline. therefore, it must be defective in synthesizing Citrulline~ornithine piled up

27. One Gene, One Enzyme Hypothesis -Beadle & Tatum • each gene dictates the production of one enzyme • each mutant lacks the ability to produce an enzyme

28. *Some proteins are not enzymes (ex. insulin) *Some proteins are made of more than one polypeptide chain (hemoglobin) *Each chain specified by its own gene One Gene, One Polypeptide Hypothesis -Beadle & Tatum (revisited)

29. How are enzymes (proteins/polypeptides) made?

30. How do we get from DNA to protein?

31. RNA

32. RNA is the bridge between DNA and Protein mRNA tRNA

33. This is the basic process: TRANSCRIPTION TRANSLATION

34. No nucleus, protein synthesis occurs same time as transcription. Transcription occurs in nucleus-> pre -mRNA Translation occurs on ribos.

35. DNA --> RNA --> PROTEIN!

36. Triplets - series of three nucleotides- code for Amino Acids U not T

37. (1961)MarshallNirenberg deciphered first codon.

38. (1961)MarshallNirenberg deciphered first codon. Won Nobel prize in Physiology and Medicine 1968 for the interpretation of the genetic code and its function in proteinsynthesis.

40. 1965 Dictionary of Amino Acids This is the same for ALL species of organisms

41. 1965 Dictionary of Amino Acids Evolutionary Significance??

42. Code Redundancy • Third base in a codon shows "wobble”. • First two bases are the most important in reading the code and giving the correct AA. The third base often doesn’t matter.