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Nucleic Acid


  1. DNA
    1. It is the chemical basis of heredity and is organized into genes.
    2. DNA contains genetic information was first demonstrated by Avery, Macleod, and McCarty, in 1944,using pneumococcus.
    3. DNA contains 4 deoxynucleosides-A,T,C and G. These monomeric units are held together by3’,5’-phosphodiester bridges into polymeric form
    4. The 2 strands of double stranded DNA are held by Hydrogen bond. A bonds with T and C bonds with G
    5. The common form of DNA is right handed
    6. The 2 strands are antiparallel to each other.
    7. Double stranded DNA can be melted into 2 separate strands by increasing temperature and decreasing salt concentration.
    8. DNA provides template for replication and transcription.
      1. The two strands of DNA are not straight, they are twisted around each other to form a double helix. Each turn of helix contains ten base pairs.
      2. The diameter of helix is 20A0. Adjacent bases are separated by 3.4 A0 along the helix axis and the pitch (vertical distance per turn) is 34A0 as there are 10 base pairs per turn.
      3. The two strands have opposite polarity, i.e. they run parallel but in opposite direction. Two grooves are seen in double helix, which are termed as the major groove and minor groove.


All the purine and pyrimidine bases present on one strand of molecule take part in hydrogen bonding with
complementary bases on opposite strand.


  1. In RNA the sugar is ribose. It is single stranded and can be easily hydrolyzed by alkali.
  2. It has uracil instead of Thymine.
  3. 3 main classes of RNAs exist: mRNA, tRNA and rRNA
    1. mRNA-convey information in gene to protein synthesizing machinery
    2. tRNA-serve as adapters for translation ,20 species, one for each amino acid
    3. rRNA-acts as a machinery for protein synthesis, site of interaction of mRNA and tRNA
  4. Small stable RNA - involved in RNA processing and gene regulation.


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