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  • (a) State the ‘Central dogma’ as proposed by Francis Crick. Are there any exceptions to it ? Support your answer with a reason and an example.  (b) Explain how the biochemical characterisation (nature) of ‘Transforming

(a) State the ‘Central dogma’ as proposed by Francis Crick. Are there any exceptions to it ? Support your answer with a reason and an example. 

(b) Explain how the biochemical characterisation (nature) of ‘Transforming Principle’ was determined, which was not defined from Griffith’s experiments. 

 

 

 

 
 
 
 
 

Answers (1)

a) Francis Crick proposed the Central dogma in molecular biology, which states that the genetic information flows from DNA→RNA→Protein. 
  
 Exceptions to Central Dogma- 
An exception to the central dogma - The biggest revolution in the central dogma was the discovery of retroviruses, which transcribe RNA into DNA with the use of a special enzyme called reverse transcriptase produced by some viruses. The resulting flow of information was RNA → DNA → RNA → proteins. This was discovered by H. Temin and D. Baltimore. 
Another exception is the discovery of Prions. The resulting flow of information is Protein → Protein. That is, proteins directly replicating themselves by making conformational changes in other proteins. 
 
 
b) 

  •  Prior to the work of Oswald Avery, Colin MacLeod and Maclyn McCarty (1933-44), the genetic material was thought to be a protein.
  •   They worked to determine the biochemical nature of ‘transforming principle’ in Griffith's experiment.  
  •  They purified biochemicals (proteins, DNA, RNA, etc.) from the heat-killed S cells to see which ones could transform live R cells into S cells.  
  •  They discovered that DNA alone from S bacteria caused R bacteria to become transformed.  
  •  They also discovered that protein-digesting enzymes (proteases) and RNA-digesting enzymes (RNases) did not affect transformation, so the transforming substance was not a protein or RNA.
  •  Digestion with DNase did inhibit transformation, suggesting that the DNA caused the transformation.
  •  They concluded that DNA is the hereditary material. 
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Priyanka Kumari

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