Answer:
Each base pair is formed from two complementary nucleotides (purine with pyrimidine) bound together by hydrogen bonds. The base pairs in DNA are adenine with thymine and cytosine with guanine. DNA has a spiral staircase-like structure.
Explanation:
DNA molecule is a double helix, having four base pairs, that is adenine, guanine, thymine, and cytosine. Adenine pairs with thymine, and cytosine pairs with guanine.
• The discovery of DNA was done by Watson and Crick.
• DNA exhibits two strands or sides, and these strands are present in the form of a twisted ladder, giving it a look of a double helix.
• In the ladder, the sides constitute the sugar-phosphate parts of adjacent nucleotides bonded together.
• Covalent bonding is found between the phosphate of one nucleotide and the sugar of the next nucleotide.
• Between the phosphates, the hydrogen bonds make the strand of the DNA twist.
• The nitrogenous bases on the ladder are pointed inward and form pairs with the bases present on the other side.
• The complementary pairing of the bases is done, that is, purine pairs with pyrimidines with the help of hydrogen bonds.
• Pairing is done between adenine and thymine and between cytosine and guanine.
Thus, DNA is a double helical molecule having complementary base pairing, that is, purines with pyrimidines.
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