Question

Explain the double helix structure of DNA with a labelled diagram.

Answer 1

• DNA has a double-stranded helical structure.
• It was given by Watson and Crick model.
• It is also known as B form of DNA.
• It is made up of nitrogenous base, deoxyribose sugar, and phosphate.
• The nitrogenous base, deoxyribose sugar, and phosphate link together forms the nucleotide chain.
• The two nucleotide chain is arranged as stacks connected by phosphate.
• The phosphate connects the 3' carbon atom of one sugar molecule and the 5' carbon atom of another deoxyribose sugar of next nucleotide chain by phosphodiester bonds.
• 3'-5' linkage by phosphodiester bonds makes the two strands as antiparallel strands.
• Nitrogenous base is of two types purines and pyrimidines.
• Adenine and guanine is purines, while thymine and cytosine is pyrimidines.
  
• Purines are linked to pyrimidines by hydrogen bonds.
• The adenine and thymine is linked by two hydrogen bonds while cytosine and guanine is linked by three hydrogen bonds.
• The nitrogenous bases are linked to the sugar by N-glycosidic bonds.
• It has a diameter of 20 A${}^0$.
• The total helix runs to a length of 34A${}^0$.
• The axial rise per base pair is 3.4 A${}^0$.
• Base pair per turn is 10A${}^0$.