DNA QUESTION 1985:				      L. PETERSON/AP BIOLOGY

	Describe the operon hypothesis and discuss how it explains the control of 
	messenger RNA production and the regulation of protein synthesis in 
	bacterial cells.
 
  
  STANDARDS:
  
  BACKGROUND:                           Max. = 2 points
  
  __  Definition of operon (functionally related genes whose expression is controlled)
  __  DNA consists of genes coding for both structural and regulating proteins 
         (Hypothesis)
  __  Authors of Hypothesis
  
  DESCRIPTION OF OPERON (likely the Lac Operon):  Max. = 8 points
  
        Structure (diagram)                  Max. 4
  __  promoter site
  __  repressor site
  __  operator site
  __  structural genes
  __  inducer
        Function                             Max. 4
  __  binds RNA polymerase* at 3' site on DNA (* also cAMP-CAP)
  __  produces repressor protein: stops RNA polymerase attaching to promoter
  __  site of attachment of repressor protein
  __  codes for sequential protein
  __  serves to inactivate repressor
  
  CONTROL OF mRNA PRODUCTION & CONSEQUENCES re PROTEIN SYNTHESIS: 
  
  __  Inducible model: derepression (lactose example) [gene always off] = 3 points
  __  Repressible model: corepression (tryptophan-histidine) [gene always on] 
                                                    = 3 points     
  __  CAP model: catabolite induction: with decrease in glucose -> increase in cAMP
           cAMP-CAP binds to promoter site
           therefore, transcription -> lactose metabolism  = 3 points
        (above require explanation & example)
  __  Adaptive significance = 2 points
  __  Final fate of mRNA transcribed = 2 points
                                        Max. = 5