L6: DNA is the genetic material

• Who presented the concept of 'the inborn error of metabolism' in 1902?

  Sir Archibald Garrod
• What is albinism characterized by?

  Lack of pigment
• What condition is associated with the secretion of homogentisic acid into urine?

  Alkaptonuria
• What hypothesis did Beadle and Tatum propose in 1941?

  One gene-one enzyme
• What organism did Beadle and Tatum use as a model for their experiments?

  Neurospora crassa
• What is the life cycle of Neurospora crassa characterized by?

  Haploid and multinucleate stages
• What question did Beadle and Tatum seek to answer regarding gene function?

  Does one gene control the whole conversion or is there a separate gene for each step?
• What is an auxotroph?

  A mutant that requires a particular additional nutrient
• Why is there only one copy of each gene in a haploid colony?

  Because haploid organisms have a single set of chromosomes
• What was the purpose of transferring each survivor to a culture tube containing complete medium?

  To identify potential nutritional requirements
• What does failure to grow on minimal medium indicate?

  A potential nutritional requirement
• What does growth on minimal medium containing amino acids indicate?

  A requirement for an amino acid
• What identifies a requirement for arginine in Beadle and Tatum's experiment?

  Growth on minimal medium supplemented with arginine
• What conclusion did Beadle and Tatum reach regarding arginine auxotrophs?

  A gene controlled each step of arginine biosynthesis
• How did Beadle and Tatum's hypothesis evolve over time?

  It became known as one gene-one protein
• Who discovered nucleic acid in 1869?

  Friedrich Miescher
• What unexpected property did Miescher find in nuclein?

  It was rich in phosphorus with no detectable sulfur
• What did Frederick Griffith demonstrate in 1928?

  Bacterial transformation
• What is the Central Dogma of molecular biology?

  DNA is transcribed to RNA, which is then translated into protein.
• Who discovered nucleic acid and in what year?

  Friedrich Miescher discovered nucleic acid in 1869.
• What unexpected properties did Miescher find in the substance he called 'nuclein'?

  It contained carbon, nitrogen, hydrogen, and was rich in phosphorus with no detectable sulfur.
• What did Frederick Griffith demonstrate in 1928?

  He demonstrated bacterial transformation.
• What is the significance of the transforming principle in Griffith's experiments?

  It is the factor that allows a bacterium to change its form and function.
• What was the outcome when mice were injected with living R cells in Griffith's experiments?

  The mice remained healthy and living R cells could be recovered from their heart tissue.
• What happened when mice were injected with living S cells?

  The mice contracted pneumonia and living S cells could be recovered from their heart tissue.
• What was the result of injecting mice with heat-killed S cells?

  The mice remained healthy and no living streptococci could be recovered from their heart tissue.
• What was the outcome when mice were injected with a mixture of heat-killed S cells and living R cells?

  Both R and S cells could be recovered from the mouse heart tissue.
• What did the experiments in 1944 reveal about the transforming principle?

  The transforming principle is DNA.
• What did the Avery-MacLeod-McCarty experiments demonstrate regarding DNase?

  DNase destroys the transforming principle.
• Why were the results of the Avery-MacLeod-McCarty experiments not well received at the time?

  Scientific opinion favored protein as the hereditary material due to earlier experimental approaches.
• Who examined the functions of protein and DNA in bacteriophage T2 in 1952?

  Alfred D. Hershey and Martha Chase.
• What did Hershey share a Nobel Prize for in 1969?

  For discoveries concerning the replication mechanism and the genetic structure of viruses.
• What is the structure of phage T2 composed of?

  It consists of a base plate, tail fibers, a core, and a sheath surrounding DNA.
• What was unknown about the role of protein and DNA in T2 phage research from 1948 to 1952?

  The role that each substance played in infection was unknown.
• How did Martha Chase trace the fate of phage protein and DNA?

  She labelled them radioactively with sulfur and phosphorus, respectively.
• What was the outcome of the experiment with 35S labelled protein?

  No inheritance of 35S was observed, indicating protein is not the genetic material.
• What was the outcome of the experiment with 32P labelled DNA?

  Inheritance of 32P was observed, indicating DNA is the genetic material.
• Why was Hershey cautious in interpreting his results?

  He did not want to state definitively that DNA was the likely genetic material.
• What are the key historical milestones in the understanding of DNA as the genetic material?

  • 1869: Miescher discovers nucleic acid.
  • 1928: Griffith demonstrates bacterial transformation.
  • 1944: Avery et al. provide evidence that DNA is the hereditary material.
  • 1952: Hershey and Chase confirm DNA as the genetic material.
  • 1958: Central Dogma established.