DNA QUESTION 1984:				L. PETERSON/AP BIOLOGY

	Experiments by the following scientists provided critical information 
	concerning DNA. Describe each classical experiment and indicate how 
	it provided evidence 	for the chemical nature of the gene.
		a.  Hershey and Chase - bacteriophage replication
		b.  Griffith and Avery - bacterial transformation
		c.  Meselson and Stahl - DNA replication in bacteria

  
  STANDARDS: one point for each of the following with a max. of 6 points per section
  
  EXPERIMENTS OF HERSHEY AND CHASE:
  
  __  Hypothesis or problem statement
  
  Experimental procedure:
  __  phage cultured in 32P and 35S labeled E. coli
  __  recovery of labeled virus
  __  reinfection of cold bacteria with hot virus
  
  Results:
  __  recovery of endogenous 32P label
  __  recovery of exogenous 35S label
  __  recognition of protein (35S) and DNA (32P) association
  __  Interpretation and Extension to DNA as genetic material
  
  EXPERIMENTS OF GRIFFITH AND AVERY:
  
  __  Hypothesis or problem statement
  __  Restatement of Griffith's work (in vivo)
  __  Description of Griffith's work
  __  Recognition of "transforming principle"
  
  Description of Avery, MacLeod and McCarty's work:
  __  In vitro mix of inactivated III S cocci and active II R cocci 
         leads to small number of plated III S forms
  __  Exposure of II R cocci to DNA extracted from III S phenotype
  __  Transformation of II R to III S DNA (DNAase implications)
  __  Interpretation 
  
  EXPERIMENTS OF MESELSON AND STAHL:
  
  __  Hypothesis or problem statement
  __  Description of the design of Meselson and Stahl's Experiment
  __  In vitro work with E.coli using nutrients with 15N or heavy nitrogen
  __  Use of density gradient centrifugation
  __  Parent DNA (strands heavy) -> Offspring DNA (one strand heavy/one strand light)
  __  Interpretation of results: Semiconservative Replication