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Section: Genetics » Chemistry of the Gene » Nucleic Acids and Their Structure
 
 
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Content
⇒ Chemistry of the Gene 1.  Nucleic Acids and Their Structure
⇒ Nucleic acids as genetic material
⇒ Transformation experiments
⇒ Experiments with bacteriophage (T2) infection
⇒ Experiments with tobacco mosaic virus (TMV)
⇒ Structure of nucleic acids 
⇒ Bases
⇒ Nucleosides
⇒ Nucleotides
⇒ Polynucleotide
⇒ Deoxyribonucleic acid (DNA)
⇒ Alternative forms of DNA double helices
⇒ Z-DNA, a left handed DNA form
⇒ RL model
⇒ Supercoils in closed DNA
⇒ Ribonucleic acid (RNA)


The bases are of two types namely- (i) pyrimidines and (ii) purines. The pyrimidine ring can be numbered in two different manners (Fig. 25.8). Only the old numbering system will be followed in this book. There are three main pyrimidine bases found in nucleic acid, namely thymine, cytosine and uracil (Fig. 25.9). While cytosine and thymine are commonly found in DNA, cytosine and uracil are found in RNA. In RNA, thymine is replaced by uracil. Similarly, there are two main purine bases, adenine and guanine (Fig. 25.10).
  
Numbering of carbon atoms in a pyridine ring.
Fig. 25.8. Numbering of carbon atoms in a pyridine ring.

Structure of different pyrimidines
Fig. 25.9. Structure of different pyrimidines
 
Structure of two purines.
Fig. 25.10. Structure of two purines.


 
     






     
     
 
 
     
 
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