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CBSE Class 12-science Answered

Give an account on double helix model for structures DNA 

Asked by lobilopatz | 16 Jun, 2019, 08:54: AM
Expert Answer

The three-dimensional structure of DNA was discovered in 1953 by Watson and Crick for which work they won a Nobel Prize. The main features of the structure are:

  • DNA is double-stranded, so there are two polynucleotide stands alongside each other.
  • Each single strand of DNA is made of repeating units of nucleotides.
  • Single nucleotide is made up of: pentose sugar (deoxyribose sugar), phosphate group and nitrogenous bases.
  • The strands are complementary and antiparallel i.e. they run in opposite directions thus 5' to 3' is parallel to 3' to 5'.
  • The two strands are wound round each other to form a double helix.
  • The two strands are joined together by hydrogen bonds between the nitrogenous bases.
  • The bases therefore form base pairs, which are like rungs of a ladder.
  • The base pairs are specific. A only binds to T by a double bond of hydrogen) and C only binds to G by triple bond of hydrogen.
  • These are called complementary base pairs. This means that whatever the sequence of bases along one strand, the sequence of bases on the other stand must be complementary to it.
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