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TYPES OF DNA AND DIFFERENT FORMS OF DNA

  Types of DNA A DNA A DNA appears when the DNA fibre (B DNA) is dehydrated ADNA is right handed double helix . Rise per base pair 2.3 𝐴 ̂   Rotation per base pair in ADNA is 32-72 𝐴 ̂   The diameter of ADNA helix is 25.5 𝐴 ̂   The helix of ADNA is wider and shorter than that of BDNA  The minor groove is practically non existant in A-DNA. B DNA/DOUBLE STRANDED DNA It is a common DNA. It is present in all living organism It represent the Watson and crick model of DNA. C DNA CDNA is formed at 66% relative humidity in presence of Li ions This form of DNA is also right handed with an axial rise of 3.32 𝐴 ̂    per base pair There are 9-33 base pair per turn of helix the value of helix path is 30-97 𝐴 ̂   The rotation per base pair in C-DNA is 38.58 𝐴 ̂   The C-helix has diameter of 19 𝐴 ̂   D DNA DNA is a rare variant with only 8 base pair per helical turn This form of DNA is devoid of guanine. There is a ...
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TYPES OF DNA AND DIFFERENT FORMS OF DNA

 Types of DNA

A DNA

  • A DNA appears when the DNA fibre (B DNA) is dehydrated
  • ADNA is right handed double helix .
  • Rise per base pair 2.3 𝐴 ̂  
  • Rotation per base pair in ADNA is 32-72 𝐴 ̂  
  • The diameter of ADNA helix is 25.5 𝐴 ̂  
  • The helix of ADNA is wider and shorter than that of BDNA 
  • The minor groove is practically non existant in A-DNA.

B DNA/DOUBLE STRANDED DNA

  • It is a common DNA. It is present in all living organism
  • It represent the Watson and crick model of DNA.

C DNA

  • CDNA is formed at 66% relative humidity in presence of Li ions
  • This form of DNA is also right handed with an axial rise of 3.32 𝐴 ̂    per base pair
  • There are 9-33 base pair per turn of helix the value of helix path is 30-97 𝐴 ̂  
  • The rotation per base pair in C-DNA is 38.58 𝐴 ̂  
  • The C-helix has diameter of 19 𝐴 ̂  

D DNA

  • DNA is a rare variant with only 8 base pair per helical turn
  • This form of DNA is devoid of guanine.
  • There is a axial rise of 3.03 𝐴 ̂   base pair with tilting of 16.7 𝐴 ̂   from the axis of helix 

Z-DNA

  • Z-DNA is left handed double helix and the phosphate in the DNA on back bone are in zigzag manner and the repeating sugar residue have alternating orientation. 
  • ZDNA has only one deep helical groove.
  • There are 12 base pairs per helical turn with axial rise of 3.8 𝐴 ̂  .
  • The diameter of ZDNA is 18.4 𝐴 ̂  
  • It has left handed rotation.
  • The ZDNA tracts undefined role in regulation of expression of some genes or in genetic recombination.


DIFFERENT  FORMS OF DNA

HDNA

  • It is unusual DNAstructure polypyrimidines/polypurines tracts which incorporate a mirror repeat within a sequence.

  • The novel feature of HDNA is the pairing and interwinding of three strands of DNA to form triple helix.
  • Triple helical DNA forms spontaneously within a long sequences containing only pyrimidines in one strand.
  • Two of 3 strands in HDNA triple helix contains pyrimidines and third contains purines.

SINGLE STRANDED DNA

  • The DNA is not always a double helical structure.
  • DNA of several groups of small bacterial viruses exist normally as single stranded molecule.
  • This single stranded DNA having same chemical composition as in double stranded DNA.

CIRCULAR DNA

  • In some organism bacteria, bacteriophage and many DNA containing animal viruses the two end of DNA are joined to create a closed circle with no terminus
  • The πœ†-bacteriophage can interconvert between linear and circular form 

References
1.Principles of Biochemistry-Lehinger 
2.Biochemistry-U. Sathyanarayana & U.Chakrapani








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