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Dna as a geneticmaterial

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The document discusses evidence that DNA is the genetic material: 1) Griffith's experiment showed bacterial transformation from non-virulent to virulent strains upon uptake of DNA from heat-killed bacteria. 2) Avery, MacLeod and McCarty's experiment showed transformation only occurred when DNA was present, as DNase treatment prevented transformation. 3) Hershey and Chase's experiment using radioactive labels showed that only bacteriophage DNA, not protein, entered bacteria to produce new phage particles.

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11/11/161 DNA AS GENETIC MATERIAL
• It is well known fact that transmission of traits takes place from one generation to other. The offsprings are similar to both the parents in some traits • Gregor Johann Mendel (1866 ) on the basis of his hybridization experiments on Sweet pea gave the idea that transmission of traits over generations take place through Factor or Determiner or Gene which carries information for expression of trait or phenotype. • Genes are present on the chromosomes which are distributed equally into the two daughter cells during cell division. 11/11/162
Genetic material must be capable of • Replication ( Make its copy ) • Storage of information for expression of trait • Control expression of traits • Change in controlled way (undergo mutation) • Must be stable 11/11/163
• Topic of Discussion till 1944 was which chromosomal component DNA or Protein carries hereditary information or is the genetic material • Untill 1940 Proteins were considered as genetic material as Proteins are polymer of 20 protein amino acids and present in larger quantity, encode more and variety of information. • DNA is polymer of only 4 different deoxyribonucleotides (ATP, CTP, GTP & TTP) and is present in smaller quantity 11/11/164 Is the Genetic Material Protein or DNA
But On the basis of certain experiments conducted from time to time ,it was ultimately demonstrated that DNA carries genetic information and not the proteins 11/11/165 Direct evidences come from : • Frederick Griffith’s (1928) experiment on Bacterial Transformation • Oswald Avery, Colin Macleod and Maclyn McCarty’s (1944 ) experiment on Transformation • Alfred D. Hershey and Martha Chase (1952 ) experiment on T- Even (2,4 ) Bacteriophage
Frederick Griffith (1928) Studied Diplococcus pneumoniae, having Two strains • SIII strain was virulent, possessed a lipopolysaccharide capsule and could kill mice by causing disease Pneumonia and made round colonies on a culture plate • RII strain was avirulent and lacked a Lipopolysaccharide (LPS) capsule, growing in rough–shaped colonies on a culture plate 11/11/166
Griffith’s Experiment 11/11/167  RII SIII transformation takes place in step 4 give clue for DNA as genetic material 1 2 3
S N STEPS RESULT I Mouse injected with SIII strain Mouse died √ II Mouse injected with RII strain Mouse survived III Mouse injected with Heat Killed SIII strain Mouse survived IV Mouse injected with Heat Killed SIII & living R II strain Mouse died & from its blood live SIII √ strain bacteria recovered V Mouse injected with Heat Killed SIII+ living RII strain + DNase enzyme Mouse survived VI Mouse injected with Heat Killed SIII+ living RII strain + Protease enzyme Mouse died of √ Pneumonia STEPS AND RESULTS OF GRIFFITH’S EXPERIMENT 11/11/168
GRIFFITH’S CONCLUSION •On the basis of Result of step IV Griffith concluded that there was transformation of Avirulent RII type to Virulent SIII type by picking up the genetic material encoding the LPS capsule from the Heat Killed S III . •This bacterial transformation clearly shows the role of DNA as Genetic Material and is further confirmed by results of step V which shows no transformation as DNase digests DNA and step VI again shows transformation as protease only digests protein • DNA-digesting enzymes destroyed all transforming ability •The transforming material is DNA 11/11/169
11/11/1610 Avery, MacLeod AND McCarty EXPERIMENT  Is based on transformation  Cell free extract of SIII strain Bacterium was subjected to DNase,RNase and Protease  Each treated extract was mixed with RII and mixture injected to mouse to see transformation.  In case of Protease and RNase transformation was recorded  In case of DNase no transformation was recorded
11/11/1611 Hershey AND Chase Experiment •Alfred Hershey and Martha Chase, 1952 investigated bacteriophages: viruses that infect bacteria •- the bacteriophage was composed of only DNA and protein •- they wanted to determine which of these molecules is the genetic material that enters into the bacteria
HERSHEY & CHASE (1952) EXPERIMENT WITH T2 BACTERIOPHAGE • In culture I Bacteriophage was grown in medium containing Radioactive Phosphorus (32 P))To make DNA Radioactive • In culture II Bacteriophage was grown in medium containing radioactive Sulphur (35 S) To make proteins Radioactive • Both kinds of Bacteriophage particles were allowed to infect Bacteria • The infected bacteria were observed for radioactivity • Radioactive Phosphorus was found with bacterial cells • Radioactive Sulphur was not traced in bacterial cells • Bacteriophage progeny carried only radioactive phosphorus and not radioactive sulphur 11/11/1612
11/11/1613
HERSHAY & CHASE CONCLUSION • As coat of Bacteriophage were not labelled with 32P and only with 35S. • The results of experiment clearly indicate that only DNA and not the proteins enter the bacterial cell. Protein coat is left outside . The DNA entering the host cell carries all the genetic information for synthesis of new phage particle. • This certainly proves that DNA is the genetic material in Bacteriophage and not proteins 11/11/1614
11/11/1615 - Bacteriophage DNA was labeled with radioactive phosphorus (32 P) - Bacteriophage protein was labeled with radioactive sulphur (35 S) - Radioactive molecules were tracked - only the bacteriophage DNA (as indicated by the 32 P) entered the bacteria and was used to produce more bacteriophage Conclusion: DNA is the genetic material Summary of Hershey & Chase (1952 ) experiment
INDIRECT EVIDENCES FOR DNA AS GENETIC MATERIAL • Presence of DNA regularly in nuclei of all types of cells • Equal amount of DNA is present in all cells of an organism • Amount of DNA is proportional to the ploidy of cell . Haploid cells have ½ the amount of DNA than diploid cell. • Nuclear Division occurs only after DNA duplication during S phase of Interphase • Variation in Diploid amount of DNA amongst different species 11/11/1616
SUMMARY OF THE PRESENTAION ON DNA AS GENETIC MATERIAL • Gene (Mendelian Factor) carries information for expression of Phenotype. • Genes are present on chromosomes. • The chromosomes contain 60% protein and 40% DNA. • Genetic Material must be stable, capable of replication, storing information for expression and undergo mutation. • Expression is controlled through Central Dogma of Molecular Biology involving Replication ,Transcription and Translation. 11/11/1617
DNA preRNA RNA Protein DNA Replication & Repair Transcription Processing Translation Folding Assembly Processing Central Dogma THE MODERN FRAME WORK OF MOLECULAR BIOLOGY 11/11/1618
11/11/1619 END OF PRESENTATION

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Dna as a geneticmaterial

  • 2. • It is well known fact that transmission of traits takes place from one generation to other. The offsprings are similar to both the parents in some traits • Gregor Johann Mendel (1866 ) on the basis of his hybridization experiments on Sweet pea gave the idea that transmission of traits over generations take place through Factor or Determiner or Gene which carries information for expression of trait or phenotype. • Genes are present on the chromosomes which are distributed equally into the two daughter cells during cell division. 11/11/162
  • 3. Genetic material must be capable of • Replication ( Make its copy ) • Storage of information for expression of trait • Control expression of traits • Change in controlled way (undergo mutation) • Must be stable 11/11/163
  • 4. • Topic of Discussion till 1944 was which chromosomal component DNA or Protein carries hereditary information or is the genetic material • Untill 1940 Proteins were considered as genetic material as Proteins are polymer of 20 protein amino acids and present in larger quantity, encode more and variety of information. • DNA is polymer of only 4 different deoxyribonucleotides (ATP, CTP, GTP & TTP) and is present in smaller quantity 11/11/164 Is the Genetic Material Protein or DNA
  • 5. But On the basis of certain experiments conducted from time to time ,it was ultimately demonstrated that DNA carries genetic information and not the proteins 11/11/165 Direct evidences come from : • Frederick Griffith’s (1928) experiment on Bacterial Transformation • Oswald Avery, Colin Macleod and Maclyn McCarty’s (1944 ) experiment on Transformation • Alfred D. Hershey and Martha Chase (1952 ) experiment on T- Even (2,4 ) Bacteriophage
  • 6. Frederick Griffith (1928) Studied Diplococcus pneumoniae, having Two strains • SIII strain was virulent, possessed a lipopolysaccharide capsule and could kill mice by causing disease Pneumonia and made round colonies on a culture plate • RII strain was avirulent and lacked a Lipopolysaccharide (LPS) capsule, growing in rough–shaped colonies on a culture plate 11/11/166
  • 7. Griffith’s Experiment 11/11/167  RII SIII transformation takes place in step 4 give clue for DNA as genetic material 1 2 3
  • 8. S N STEPS RESULT I Mouse injected with SIII strain Mouse died √ II Mouse injected with RII strain Mouse survived III Mouse injected with Heat Killed SIII strain Mouse survived IV Mouse injected with Heat Killed SIII & living R II strain Mouse died & from its blood live SIII √ strain bacteria recovered V Mouse injected with Heat Killed SIII+ living RII strain + DNase enzyme Mouse survived VI Mouse injected with Heat Killed SIII+ living RII strain + Protease enzyme Mouse died of √ Pneumonia STEPS AND RESULTS OF GRIFFITH’S EXPERIMENT 11/11/168
  • 9. GRIFFITH’S CONCLUSION •On the basis of Result of step IV Griffith concluded that there was transformation of Avirulent RII type to Virulent SIII type by picking up the genetic material encoding the LPS capsule from the Heat Killed S III . •This bacterial transformation clearly shows the role of DNA as Genetic Material and is further confirmed by results of step V which shows no transformation as DNase digests DNA and step VI again shows transformation as protease only digests protein • DNA-digesting enzymes destroyed all transforming ability •The transforming material is DNA 11/11/169
  • 10. 11/11/1610 Avery, MacLeod AND McCarty EXPERIMENT  Is based on transformation  Cell free extract of SIII strain Bacterium was subjected to DNase,RNase and Protease  Each treated extract was mixed with RII and mixture injected to mouse to see transformation.  In case of Protease and RNase transformation was recorded  In case of DNase no transformation was recorded
  • 11. 11/11/1611 Hershey AND Chase Experiment •Alfred Hershey and Martha Chase, 1952 investigated bacteriophages: viruses that infect bacteria •- the bacteriophage was composed of only DNA and protein •- they wanted to determine which of these molecules is the genetic material that enters into the bacteria
  • 12. HERSHEY & CHASE (1952) EXPERIMENT WITH T2 BACTERIOPHAGE • In culture I Bacteriophage was grown in medium containing Radioactive Phosphorus (32 P))To make DNA Radioactive • In culture II Bacteriophage was grown in medium containing radioactive Sulphur (35 S) To make proteins Radioactive • Both kinds of Bacteriophage particles were allowed to infect Bacteria • The infected bacteria were observed for radioactivity • Radioactive Phosphorus was found with bacterial cells • Radioactive Sulphur was not traced in bacterial cells • Bacteriophage progeny carried only radioactive phosphorus and not radioactive sulphur 11/11/1612
  • 14. HERSHAY & CHASE CONCLUSION • As coat of Bacteriophage were not labelled with 32P and only with 35S. • The results of experiment clearly indicate that only DNA and not the proteins enter the bacterial cell. Protein coat is left outside . The DNA entering the host cell carries all the genetic information for synthesis of new phage particle. • This certainly proves that DNA is the genetic material in Bacteriophage and not proteins 11/11/1614
  • 15. 11/11/1615 - Bacteriophage DNA was labeled with radioactive phosphorus (32 P) - Bacteriophage protein was labeled with radioactive sulphur (35 S) - Radioactive molecules were tracked - only the bacteriophage DNA (as indicated by the 32 P) entered the bacteria and was used to produce more bacteriophage Conclusion: DNA is the genetic material Summary of Hershey & Chase (1952 ) experiment
  • 16. INDIRECT EVIDENCES FOR DNA AS GENETIC MATERIAL • Presence of DNA regularly in nuclei of all types of cells • Equal amount of DNA is present in all cells of an organism • Amount of DNA is proportional to the ploidy of cell . Haploid cells have ½ the amount of DNA than diploid cell. • Nuclear Division occurs only after DNA duplication during S phase of Interphase • Variation in Diploid amount of DNA amongst different species 11/11/1616
  • 17. SUMMARY OF THE PRESENTAION ON DNA AS GENETIC MATERIAL • Gene (Mendelian Factor) carries information for expression of Phenotype. • Genes are present on chromosomes. • The chromosomes contain 60% protein and 40% DNA. • Genetic Material must be stable, capable of replication, storing information for expression and undergo mutation. • Expression is controlled through Central Dogma of Molecular Biology involving Replication ,Transcription and Translation. 11/11/1617
  • 18. DNA preRNA RNA Protein DNA Replication & Repair Transcription Processing Translation Folding Assembly Processing Central Dogma THE MODERN FRAME WORK OF MOLECULAR BIOLOGY 11/11/1618