1 Chapter 15 EXPRESSION of BIOLOGICAL INFORMATION

2 DNA & Genetic Information Objectives to describe the structure of DNA based on the Watson & Crick model to explain DNA as the carrier of genetic information to explain the concept of one gene one polypeptide

DNA STRUCTURE 3 Watson and Crick Model Monomer : NUCLEOTIDE Component : Deoxyribose (pentose sugar) Phosphate group Nitrogenous base : Adenine (A) Thymine (T) Guanine (G) Cytosine (C) *Base pairing rule : A-T and C-G

DNA NUCLEOTIDE 4

WATSON AND CRICK MODEL 5 DNA : 2 polynucleotide chain Arrange in double helix Nucleotide link by alternating sugar-phosphate backbone : phosphodiester bond Antiparallel (3’ to 5’) and (5’ to 3’) Each polynucleotide chain attach to another polynucleotide chain by hydrogen bond

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7 DNA as carrier of genetic information Experiments are conducted by Frederick Griffith (1928) and Avery (1944) Griffith: Identify transformation process Avery et.al. : identify the transformation agent

8 Griffith (1928) - studied Streptococcus pneumoniae ; bacterium that causes pneumonia to mammals two strains (varieties) of S. pneumoniae : R (rough) strain mutant strain non-capsulated non-virulent (non-pathogenic) S (smooth) strain capsulated virulent (pathogenic / causing disease) DNA: The Carrier of Genetic Information

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Transformation occur DNA: The Carrier of Genetic Information

11 the transformed bacteria reproduce forming S strain daughter cells (heritable) transformation transformation occur; live R strain is transformed into live S strain by hereditary material obtained from the dead strain-S cells the hereditary substance was unknown DNA: The Carrier of Genetic Information

12 Definition a change in genotypes and phenotypes of an individual due to the assimilation of foreign DNA by a cell. R strain S strain DNA: The Carrier of Genetic Information

13 In 1944, Oswald Avery, Maclyn McCarty and DNA Colin McLeod proved that DNA was the transforming substance. Two models of the experiment were carried out. Transformation agent DNA: The Carrier of Genetic Information

14 Transformation agent heat-killed the S strain bacteria culture purify the culture; remove proteins, carbohydrates, lipids, RNA and DNA add proteins, carbohydrates, lipids, RNA and DNA to different cultures of living R strain Observation : After a few days, colonies of S strain grew in the R strain culture that was grew in the R strain culture that was added with DNA added with DNA Experiment 1 Experiment 1 DNA: The Carrier of Genetic Information

15 Experiment 1 Experiment 1 The observation The observation After a few days, colonies of the S strain grew in the R strain culture which had DNA added. Transformation agent 15.1 DNA: The Carrier of Genetic Information

16 S colonies extracts are added to different cultures of R strain no change carbohydratelipidproteinRNA S strain found DNA Transformation agent DNA: The Carrier of Genetic Information Transformation

17 Experiment 2 Experiment 2 Enzyme Treatment Enzyme Treatment 1. The purified DNA of the S strain bacterium was mixed with the R strain colonies. The Procedures The Procedures 2. Different enzymes 2. Different enzymes were added to the different mixture. 3. Bacteria colony was grown in different culture. Transformation agent DNA: The Carrier of Genetic Information

18 The enzymes added: protease - degrades proteins ribonuclease - RNase - degrades RNA deoxyribonuclease - DNase - degrades DNA Experiment 2 Experiment 2 Procedures Procedures Transformation agent DNA: The Carrier of Genetic Information

19 R Strain R colonies DNA from heat-killed S cells no colonies Living R Strain + DNA from heat-killed S cells + Serum that precipitates R cells from mixture S colonies (transformation) Experiment 2

20 R strain + DNA from heat-killed S cells + Serum that precipitates R cells from mixture + protease transformation R strain + DNA from heat-killed S cells + Serum that precipitates R cells from mixture + RNase transformation R strain + DNA from heat-killed S cells + Serum that precipitates R cells from mixture + DNase NO colonies Experiment 2 S colonies

21 failed The protease and the RNase failed to stop the transformation of the R strain into the S strain by the purified DNA. destroyed The DNase destroyed the transforming activity of the purified DNA preparation. Experiment 2 Experiment 2 The Inferences The Inferences Transformation agent DNA: The Carrier of Genetic Information

22 Experiment 2 Experiment 2 The Conclusion The Conclusion Transformation agent is DNA is the carrier of genetic information DNA from the capsulated bacteria (S strain) carries the gene that encode the production of capsule During transformation, the DNA is assimilated by DNA of R strain; enables R strain to synthesize capsule DNA: The Carrier of Genetic Information

23 George Beadle and Edward Tatum (1941) study the relationship between genes and enzymes by using Neurospora crassa (bread mold) fungi (Ascomycota / sac fungi) Fungi that produce spores in structures called sacs Gene concept: One-Gene-One-Polypeptide

24 Minimal medium consists of agar, glucose, inorganic salts and vitamin biotin Complete medium consists of agar, glucose, inorganic salts, vitamin biotin and 20 amino acids. Medium needed: Beadle & Tatum experiment Gene concept: One-Gene-One-Polypeptide

25 some conidia (asexual spores) were exposed to X-ray; to induce mutation Gene concept: One-Gene-One-Polypeptide Procedures

26 complete conidia (mutant) were transferred to complete medium medium and grown; mycelia formed mycelia (from mutant conidia) were crossed with mycelia (from wild type conidia). wild type conidia are NOT exposed to X-ray Gene concept: One-Gene-One-Polypeptide Procedures

27 producing asci (sin. ascus) that consist of eight ascospores (four ascospores from each parental mycelia – mutant and wild type) Gene concept: One-Gene-One-Polypeptide

28 the ascospores were dissected out and transferred to complete medium. ALL grew and formed mycelia mycelia were placed on minimal medium NO growth occur Gene concept: One-Gene-One-Polypeptide Procedures

29 mycelia which did no grow were unable to synthesize certain amino acids to determine which amino acids were synthesized, mycelia were transferred to minimal media each containing a different amino acid amino acid test Gene concept: One-Gene-One-Polypeptide

30 the medium in which growth occur, contain the amino acid which the mutant Neurospora unable to synthesize Gene concept: One-Gene-One-Polypeptide Observations

31 does not have the enzyme to synthesize arginine due to lacks of gene that encodes the enzyme results in the mutant could ONLY grow with the supply of arginine “ One GENE ; One ENZYME ” the mutant Neurospora was defective in biochemical pathway to synthesize arginine Gene concept: One-Gene-One-Polypeptide Conclusion

32 proteins that AREN’T enzymes also encoded by genes NOT all proteins are enzymes e.g keratin (structural protein) insulin (peptide hormone)  “ One GENE ; One PROTEIN ” proteins are composed of different polypeptide chains (e.g hemoglobin) each polypeptide chain is encoded by gene  “ One GENE ; One POLYPEPTIDE ” Restatement

33 the defect is in the biochemical pathways that normally synthesize arginine From further experiments From further experiments Beadle and Tatum concluded that Gene concept: One-Gene-One-Polypeptide