2. A hydrogen bond is when there is a dipole-dipole force between an electronegative atom, and a hydrogen atom, attached to oxygen, nitrogen or fluorine. Complementary base pairing is when two nucleotides on opposite DNA strands are connected with hydrogen bonds. Adenine joins with thymine, and guanine joins with cytosine. A DNA molecule is made up of two polynucleotide strands twisted around each other. The sugars and phosphates form the backbone of the molecule. Pointing inwards from this 'spine' are the bases, which pair up in specific ways. A purine always pairs with a pyrimidine, which makes a DNA double helix, a massive molecule that resembles a spiral staircase. The two strands are held by hydrogen bonds betwwen the complementary base pairs. There are ten of these pairs for each complete twist of the helix. The two strands are known as the 5' (5 prime) and 3' (3 prime) strand, named according to the numer of the carbon atom in the pentose sugar.
Question 3. How did Chargaff's data and Pauling's ideas support Watson and Crick's deductions on the structure of DNA?