Discuss the structure of DNA as proposed by Watson and Crick with diagram.(5 marks)

Dear student

Watson and crick proposed the model of DNA in 1953. The salient feature of this structure include :-

• DNA has a double helical structure.
• The helix has a diameter of 20 A.
• This helix makes a full turn at every 34 A along its length and contains a stack of ten nucleotides per turn,
• The two strands of double helix run in anti- parallel direction.
• Each DNA is made up of- a pentose sugar, nitrogenous bases, phosphate group.
• The sugar and phosphate make up the backbone while the nitrogenous bases are found in the center that hold the two strands together.
• There are 4 nitrogenous bases Adenine (A), Guanine (G), Cytosine (C), Thymine (T).
• A & G are classified as purines and C& T as pyrimidine.
• The nitrogenous base A always pairs with T and C with G.
• There are two hydrogen bonds between A & T and three hydrogen bonds between G & C.

Regards