Expression of Biological Information DNA & Genetic Information DNA as genetic material Gene hypothesis Abilities of DNA Forming new DNA Produce polypeptide Replication Protein synthesis Operon Griffith (1931) Avery et. al (1944) Beadle & Tatum (1944) Hershey & Chase
At the end of the lesson, you should be able to : Explain DNA as the carrier of genetic information. Explain gene concept : One gene one polypeptide Describe the semi-conservative replication of DNA
DNA as genetic material Carrier of genetic information
DNA as genetic material… Frederick Griffith (1931) Streptococcus pneumoniae mouse Two types Mutant type Rough, non-virulent (IIR) Wild type smooth, virulent (IIIS)
DNA as genetic material… Sample 1 Frederick Griffith (1931)
DNA as genetic material… Sample 2 Frederick Griffith (1931)
DNA as genetic material… Sample 3 Frederick Griffith (1931)
DNA as genetic material… Sample 4 Frederick Griffith (1931) Living S cells found in the blood
DNA as genetic material… Frederick Griffith (1931) conclusion Living R cells are converted to S cells. Transformation occurred. What is the transforming agent?
DNA as genetic material… Concepts of transformation Transformation is a types of genetic transfer found in bacteria. Bacteria can take up the externally DNA.
DNA as genetic material… Oswald T. Avery DNA as transforming agent Colin MacLeod Maclyn McCarty
DNA as genetic material… S strain (killed) R strain (living) + Protein destroyed RNA destroyed DNA destroyed Lipid eliminated Living S cells Living R cells No transformation DNA as transforming agent proteaseRNaseDNase centrifugation
DNA as genetic material… Avery et. al (1944) conclusion The strain without DNA caused no transformation occur. So, the transformation agent is DNA!
DNA as genetic material… Hershey and Chase Prove that DNA is the molecules that responsible as genetic information, not protein. Bacteriophages
Gene Hypothesis… George Beadle and Edward Tatum experiment: connection between genes & metabolism. Neurospora crassa as experimental organism. - short life-cycle, easily grown. Since it is haploid for much of its life cycle, mutations would be immediately expressed.
Gene Hypothesis… Neurospora crassa able to synthesize all of the amino acids and other chemicals needed for growth Mutations will affect a single genes and single enzymes in specific metabolic pathways.
Minimal Nutrient Gene Enzyme Minimal Nutrient Amino acid Mutant neurospora Wild type neurospora Case 1Case2Case 3 Amino acid
How to make sure ONE genes is only code ONE polypeptide??? Gene A Gene B Gene C Gene A Gene B Gene C Precursor Ornithine Citrulline Arginine Enzyme A Enzyme B Enzyme C + Ornithine + Citrulline + Arginine XX XX X X Is the gene A only produce enzyme A only? Is the gene B only produce enzyme B only? Is the gene C only produce enzyme C only?
Gene Hypothesis… Beadle & Tatum Experiment conclusion Each gene will produce certain enzyme (polypeptide) One gene one polypeptide.
DNA Replication Model… Proposed by Matthew Meselson (left) and Franklin W. Stahl (right) in 1958.
DNA Replication Model… DNA Replication Process of copying a double stranded DNA strand which is the two resulting double strands are identical and each of them consist of one original and one newly synthesize strand.
DNA Replication Model… Watson and Crick suggest that each strands of DNA molecule could serve as template for the synthesis of opposite strand. Each half-helix could pair with their complementary nucleotides to replace its missing partner. Will result two DNA double helices, each identical to the original.
DNA Replication Model… Meselson & Stahl (1958) Studied the replication in E. coli 3 hypotheses conservativesemiconservativedispersive Which one is the model of DNA replication?
DNA Replication Model… Meselson & Stahl (1958) Both parent strand remain together and all new copies is made. Hypothesis 1 conservative
DNA Replication Model… Meselson & Stahl (1958) The 2 strand of the parental molecule separate and each functions as a template for synthesis of a new complementary strand Hypothesis 2 semiconservative
DNA Replication Model… Meselson & Stahl (1958) Each strand of both daughter molecules contains a mixture of old and newly synthesized parts Hypothesis 3 dispersive